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v3.1
 
   1/*
   2 * Memory merging support.
   3 *
   4 * This code enables dynamic sharing of identical pages found in different
   5 * memory areas, even if they are not shared by fork()
   6 *
   7 * Copyright (C) 2008-2009 Red Hat, Inc.
   8 * Authors:
   9 *	Izik Eidus
  10 *	Andrea Arcangeli
  11 *	Chris Wright
  12 *	Hugh Dickins
  13 *
  14 * This work is licensed under the terms of the GNU GPL, version 2.
  15 */
  16
  17#include <linux/errno.h>
  18#include <linux/mm.h>
 
  19#include <linux/fs.h>
  20#include <linux/mman.h>
  21#include <linux/sched.h>
 
 
 
  22#include <linux/rwsem.h>
  23#include <linux/pagemap.h>
  24#include <linux/rmap.h>
  25#include <linux/spinlock.h>
  26#include <linux/jhash.h>
  27#include <linux/delay.h>
  28#include <linux/kthread.h>
  29#include <linux/wait.h>
  30#include <linux/slab.h>
  31#include <linux/rbtree.h>
  32#include <linux/memory.h>
  33#include <linux/mmu_notifier.h>
  34#include <linux/swap.h>
  35#include <linux/ksm.h>
  36#include <linux/hash.h>
  37#include <linux/freezer.h>
  38#include <linux/oom.h>
 
 
  39
  40#include <asm/tlbflush.h>
  41#include "internal.h"
 
  42
  43/*
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  44 * A few notes about the KSM scanning process,
  45 * to make it easier to understand the data structures below:
  46 *
  47 * In order to reduce excessive scanning, KSM sorts the memory pages by their
  48 * contents into a data structure that holds pointers to the pages' locations.
  49 *
  50 * Since the contents of the pages may change at any moment, KSM cannot just
  51 * insert the pages into a normal sorted tree and expect it to find anything.
  52 * Therefore KSM uses two data structures - the stable and the unstable tree.
  53 *
  54 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
  55 * by their contents.  Because each such page is write-protected, searching on
  56 * this tree is fully assured to be working (except when pages are unmapped),
  57 * and therefore this tree is called the stable tree.
  58 *
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  59 * In addition to the stable tree, KSM uses a second data structure called the
  60 * unstable tree: this tree holds pointers to pages which have been found to
  61 * be "unchanged for a period of time".  The unstable tree sorts these pages
  62 * by their contents, but since they are not write-protected, KSM cannot rely
  63 * upon the unstable tree to work correctly - the unstable tree is liable to
  64 * be corrupted as its contents are modified, and so it is called unstable.
  65 *
  66 * KSM solves this problem by several techniques:
  67 *
  68 * 1) The unstable tree is flushed every time KSM completes scanning all
  69 *    memory areas, and then the tree is rebuilt again from the beginning.
  70 * 2) KSM will only insert into the unstable tree, pages whose hash value
  71 *    has not changed since the previous scan of all memory areas.
  72 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
  73 *    colors of the nodes and not on their contents, assuring that even when
  74 *    the tree gets "corrupted" it won't get out of balance, so scanning time
  75 *    remains the same (also, searching and inserting nodes in an rbtree uses
  76 *    the same algorithm, so we have no overhead when we flush and rebuild).
  77 * 4) KSM never flushes the stable tree, which means that even if it were to
  78 *    take 10 attempts to find a page in the unstable tree, once it is found,
  79 *    it is secured in the stable tree.  (When we scan a new page, we first
  80 *    compare it against the stable tree, and then against the unstable tree.)
 
 
 
  81 */
  82
  83/**
  84 * struct mm_slot - ksm information per mm that is being scanned
  85 * @link: link to the mm_slots hash list
  86 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
  87 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
  88 * @mm: the mm that this information is valid for
  89 */
  90struct mm_slot {
  91	struct hlist_node link;
  92	struct list_head mm_list;
  93	struct rmap_item *rmap_list;
  94	struct mm_struct *mm;
  95};
  96
  97/**
  98 * struct ksm_scan - cursor for scanning
  99 * @mm_slot: the current mm_slot we are scanning
 100 * @address: the next address inside that to be scanned
 101 * @rmap_list: link to the next rmap to be scanned in the rmap_list
 102 * @seqnr: count of completed full scans (needed when removing unstable node)
 103 *
 104 * There is only the one ksm_scan instance of this cursor structure.
 105 */
 106struct ksm_scan {
 107	struct mm_slot *mm_slot;
 108	unsigned long address;
 109	struct rmap_item **rmap_list;
 110	unsigned long seqnr;
 111};
 112
 113/**
 114 * struct stable_node - node of the stable rbtree
 115 * @node: rb node of this ksm page in the stable tree
 
 
 
 116 * @hlist: hlist head of rmap_items using this ksm page
 117 * @kpfn: page frame number of this ksm page
 
 
 
 118 */
 119struct stable_node {
 120	struct rb_node node;
 
 
 
 
 
 
 
 
 
 121	struct hlist_head hlist;
 122	unsigned long kpfn;
 
 
 
 
 
 
 
 
 
 
 
 
 
 123};
 124
 125/**
 126 * struct rmap_item - reverse mapping item for virtual addresses
 127 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
 128 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
 
 129 * @mm: the memory structure this rmap_item is pointing into
 130 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
 131 * @oldchecksum: previous checksum of the page at that virtual address
 132 * @node: rb node of this rmap_item in the unstable tree
 133 * @head: pointer to stable_node heading this list in the stable tree
 134 * @hlist: link into hlist of rmap_items hanging off that stable_node
 
 
 135 */
 136struct rmap_item {
 137	struct rmap_item *rmap_list;
 138	struct anon_vma *anon_vma;	/* when stable */
 
 
 
 
 
 139	struct mm_struct *mm;
 140	unsigned long address;		/* + low bits used for flags below */
 141	unsigned int oldchecksum;	/* when unstable */
 
 
 142	union {
 143		struct rb_node node;	/* when node of unstable tree */
 144		struct {		/* when listed from stable tree */
 145			struct stable_node *head;
 146			struct hlist_node hlist;
 147		};
 148	};
 149};
 150
 151#define SEQNR_MASK	0x0ff	/* low bits of unstable tree seqnr */
 152#define UNSTABLE_FLAG	0x100	/* is a node of the unstable tree */
 153#define STABLE_FLAG	0x200	/* is listed from the stable tree */
 154
 155/* The stable and unstable tree heads */
 156static struct rb_root root_stable_tree = RB_ROOT;
 157static struct rb_root root_unstable_tree = RB_ROOT;
 
 
 
 
 
 
 158
 159#define MM_SLOTS_HASH_SHIFT 10
 160#define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT)
 161static struct hlist_head mm_slots_hash[MM_SLOTS_HASH_HEADS];
 162
 163static struct mm_slot ksm_mm_head = {
 164	.mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
 165};
 166static struct ksm_scan ksm_scan = {
 167	.mm_slot = &ksm_mm_head,
 168};
 169
 170static struct kmem_cache *rmap_item_cache;
 171static struct kmem_cache *stable_node_cache;
 172static struct kmem_cache *mm_slot_cache;
 173
 
 
 
 
 
 
 174/* The number of nodes in the stable tree */
 175static unsigned long ksm_pages_shared;
 176
 177/* The number of page slots additionally sharing those nodes */
 178static unsigned long ksm_pages_sharing;
 179
 180/* The number of nodes in the unstable tree */
 181static unsigned long ksm_pages_unshared;
 182
 183/* The number of rmap_items in use: to calculate pages_volatile */
 184static unsigned long ksm_rmap_items;
 185
 
 
 
 
 
 
 
 
 
 
 
 
 186/* Number of pages ksmd should scan in one batch */
 187static unsigned int ksm_thread_pages_to_scan = 100;
 188
 189/* Milliseconds ksmd should sleep between batches */
 190static unsigned int ksm_thread_sleep_millisecs = 20;
 191
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 192#define KSM_RUN_STOP	0
 193#define KSM_RUN_MERGE	1
 194#define KSM_RUN_UNMERGE	2
 195static unsigned int ksm_run = KSM_RUN_STOP;
 
 
 196
 197static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
 
 198static DEFINE_MUTEX(ksm_thread_mutex);
 199static DEFINE_SPINLOCK(ksm_mmlist_lock);
 200
 201#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
 202		sizeof(struct __struct), __alignof__(struct __struct),\
 203		(__flags), NULL)
 204
 205static int __init ksm_slab_init(void)
 206{
 207	rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
 208	if (!rmap_item_cache)
 209		goto out;
 210
 211	stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
 212	if (!stable_node_cache)
 213		goto out_free1;
 214
 215	mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
 216	if (!mm_slot_cache)
 217		goto out_free2;
 218
 219	return 0;
 220
 221out_free2:
 222	kmem_cache_destroy(stable_node_cache);
 223out_free1:
 224	kmem_cache_destroy(rmap_item_cache);
 225out:
 226	return -ENOMEM;
 227}
 228
 229static void __init ksm_slab_free(void)
 230{
 231	kmem_cache_destroy(mm_slot_cache);
 232	kmem_cache_destroy(stable_node_cache);
 233	kmem_cache_destroy(rmap_item_cache);
 234	mm_slot_cache = NULL;
 235}
 236
 237static inline struct rmap_item *alloc_rmap_item(void)
 238{
 239	struct rmap_item *rmap_item;
 240
 241	rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
 242	if (rmap_item)
 243		ksm_rmap_items++;
 244	return rmap_item;
 245}
 246
 247static inline void free_rmap_item(struct rmap_item *rmap_item)
 248{
 249	ksm_rmap_items--;
 250	rmap_item->mm = NULL;	/* debug safety */
 251	kmem_cache_free(rmap_item_cache, rmap_item);
 252}
 253
 254static inline struct stable_node *alloc_stable_node(void)
 
 255{
 256	return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
 
 
 
 
 257}
 258
 259static inline void free_stable_node(struct stable_node *stable_node)
 260{
 261	kmem_cache_free(stable_node_cache, stable_node);
 
 
 262}
 263
 264static inline struct mm_slot *alloc_mm_slot(void)
 265{
 266	if (!mm_slot_cache)	/* initialization failed */
 267		return NULL;
 268	return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
 
 
 
 
 
 269}
 270
 271static inline void free_mm_slot(struct mm_slot *mm_slot)
 272{
 273	kmem_cache_free(mm_slot_cache, mm_slot);
 
 
 
 
 
 
 274}
 275
 276static struct mm_slot *get_mm_slot(struct mm_struct *mm)
 277{
 278	struct mm_slot *mm_slot;
 279	struct hlist_head *bucket;
 280	struct hlist_node *node;
 281
 282	bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
 283	hlist_for_each_entry(mm_slot, node, bucket, link) {
 284		if (mm == mm_slot->mm)
 285			return mm_slot;
 286	}
 287	return NULL;
 288}
 289
 290static void insert_to_mm_slots_hash(struct mm_struct *mm,
 291				    struct mm_slot *mm_slot)
 292{
 293	struct hlist_head *bucket;
 294
 295	bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
 296	mm_slot->mm = mm;
 297	hlist_add_head(&mm_slot->link, bucket);
 
 298}
 299
 300static inline int in_stable_tree(struct rmap_item *rmap_item)
 301{
 302	return rmap_item->address & STABLE_FLAG;
 
 
 303}
 304
 305/*
 306 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
 307 * page tables after it has passed through ksm_exit() - which, if necessary,
 308 * takes mmap_sem briefly to serialize against them.  ksm_exit() does not set
 309 * a special flag: they can just back out as soon as mm_users goes to zero.
 310 * ksm_test_exit() is used throughout to make this test for exit: in some
 311 * places for correctness, in some places just to avoid unnecessary work.
 312 */
 313static inline bool ksm_test_exit(struct mm_struct *mm)
 314{
 315	return atomic_read(&mm->mm_users) == 0;
 316}
 317
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 318/*
 319 * We use break_ksm to break COW on a ksm page: it's a stripped down
 
 320 *
 321 *	if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
 322 *		put_page(page);
 323 *
 324 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
 325 * in case the application has unmapped and remapped mm,addr meanwhile.
 326 * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
 327 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
 
 
 
 
 328 */
 329static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
 330{
 331	struct page *page;
 332	int ret = 0;
 
 333
 334	do {
 
 
 335		cond_resched();
 336		page = follow_page(vma, addr, FOLL_GET);
 337		if (IS_ERR_OR_NULL(page))
 338			break;
 339		if (PageKsm(page))
 340			ret = handle_mm_fault(vma->vm_mm, vma, addr,
 341							FAULT_FLAG_WRITE);
 342		else
 343			ret = VM_FAULT_WRITE;
 344		put_page(page);
 345	} while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
 346	/*
 347	 * We must loop because handle_mm_fault() may back out if there's
 348	 * any difficulty e.g. if pte accessed bit gets updated concurrently.
 349	 *
 350	 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
 351	 * COW has been broken, even if the vma does not permit VM_WRITE;
 352	 * but note that a concurrent fault might break PageKsm for us.
 353	 *
 354	 * VM_FAULT_SIGBUS could occur if we race with truncation of the
 355	 * backing file, which also invalidates anonymous pages: that's
 356	 * okay, that truncation will have unmapped the PageKsm for us.
 357	 *
 358	 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
 359	 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
 360	 * current task has TIF_MEMDIE set, and will be OOM killed on return
 361	 * to user; and ksmd, having no mm, would never be chosen for that.
 362	 *
 363	 * But if the mm is in a limited mem_cgroup, then the fault may fail
 364	 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
 365	 * even ksmd can fail in this way - though it's usually breaking ksm
 366	 * just to undo a merge it made a moment before, so unlikely to oom.
 367	 *
 368	 * That's a pity: we might therefore have more kernel pages allocated
 369	 * than we're counting as nodes in the stable tree; but ksm_do_scan
 370	 * will retry to break_cow on each pass, so should recover the page
 371	 * in due course.  The important thing is to not let VM_MERGEABLE
 372	 * be cleared while any such pages might remain in the area.
 373	 */
 374	return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
 375}
 376
 377static void break_cow(struct rmap_item *rmap_item)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 378{
 379	struct mm_struct *mm = rmap_item->mm;
 380	unsigned long addr = rmap_item->address;
 381	struct vm_area_struct *vma;
 382
 383	/*
 384	 * It is not an accident that whenever we want to break COW
 385	 * to undo, we also need to drop a reference to the anon_vma.
 386	 */
 387	put_anon_vma(rmap_item->anon_vma);
 388
 389	down_read(&mm->mmap_sem);
 390	if (ksm_test_exit(mm))
 391		goto out;
 392	vma = find_vma(mm, addr);
 393	if (!vma || vma->vm_start > addr)
 394		goto out;
 395	if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 396		goto out;
 397	break_ksm(vma, addr);
 398out:
 399	up_read(&mm->mmap_sem);
 400}
 401
 402static struct page *page_trans_compound_anon(struct page *page)
 403{
 404	if (PageTransCompound(page)) {
 405		struct page *head = compound_trans_head(page);
 406		/*
 407		 * head may actually be splitted and freed from under
 408		 * us but it's ok here.
 409		 */
 410		if (PageAnon(head))
 411			return head;
 412	}
 413	return NULL;
 414}
 415
 416static struct page *get_mergeable_page(struct rmap_item *rmap_item)
 417{
 418	struct mm_struct *mm = rmap_item->mm;
 419	unsigned long addr = rmap_item->address;
 420	struct vm_area_struct *vma;
 421	struct page *page;
 422
 423	down_read(&mm->mmap_sem);
 424	if (ksm_test_exit(mm))
 425		goto out;
 426	vma = find_vma(mm, addr);
 427	if (!vma || vma->vm_start > addr)
 428		goto out;
 429	if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 430		goto out;
 431
 432	page = follow_page(vma, addr, FOLL_GET);
 433	if (IS_ERR_OR_NULL(page))
 434		goto out;
 435	if (PageAnon(page) || page_trans_compound_anon(page)) {
 
 
 436		flush_anon_page(vma, page, addr);
 437		flush_dcache_page(page);
 438	} else {
 
 439		put_page(page);
 440out:		page = NULL;
 
 441	}
 442	up_read(&mm->mmap_sem);
 443	return page;
 444}
 445
 446static void remove_node_from_stable_tree(struct stable_node *stable_node)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 447{
 448	struct rmap_item *rmap_item;
 449	struct hlist_node *hlist;
 
 
 
 
 
 
 
 
 
 450
 451	hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
 452		if (rmap_item->hlist.next)
 453			ksm_pages_sharing--;
 454		else
 
 455			ksm_pages_shared--;
 
 
 
 
 
 
 456		put_anon_vma(rmap_item->anon_vma);
 457		rmap_item->address &= PAGE_MASK;
 458		cond_resched();
 459	}
 460
 461	rb_erase(&stable_node->node, &root_stable_tree);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 462	free_stable_node(stable_node);
 463}
 464
 
 
 
 
 
 
 465/*
 466 * get_ksm_page: checks if the page indicated by the stable node
 467 * is still its ksm page, despite having held no reference to it.
 468 * In which case we can trust the content of the page, and it
 469 * returns the gotten page; but if the page has now been zapped,
 470 * remove the stale node from the stable tree and return NULL.
 
 471 *
 472 * You would expect the stable_node to hold a reference to the ksm page.
 473 * But if it increments the page's count, swapping out has to wait for
 474 * ksmd to come around again before it can free the page, which may take
 475 * seconds or even minutes: much too unresponsive.  So instead we use a
 476 * "keyhole reference": access to the ksm page from the stable node peeps
 477 * out through its keyhole to see if that page still holds the right key,
 478 * pointing back to this stable node.  This relies on freeing a PageAnon
 479 * page to reset its page->mapping to NULL, and relies on no other use of
 480 * a page to put something that might look like our key in page->mapping.
 481 *
 482 * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
 483 * but this is different - made simpler by ksm_thread_mutex being held, but
 484 * interesting for assuming that no other use of the struct page could ever
 485 * put our expected_mapping into page->mapping (or a field of the union which
 486 * coincides with page->mapping).  The RCU calls are not for KSM at all, but
 487 * to keep the page_count protocol described with page_cache_get_speculative.
 488 *
 489 * Note: it is possible that get_ksm_page() will return NULL one moment,
 490 * then page the next, if the page is in between page_freeze_refs() and
 491 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
 492 * is on its way to being freed; but it is an anomaly to bear in mind.
 493 */
 494static struct page *get_ksm_page(struct stable_node *stable_node)
 
 495{
 496	struct page *page;
 497	void *expected_mapping;
 
 498
 499	page = pfn_to_page(stable_node->kpfn);
 500	expected_mapping = (void *)stable_node +
 501				(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
 502	rcu_read_lock();
 503	if (page->mapping != expected_mapping)
 504		goto stale;
 505	if (!get_page_unless_zero(page))
 506		goto stale;
 507	if (page->mapping != expected_mapping) {
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 508		put_page(page);
 509		goto stale;
 510	}
 511	rcu_read_unlock();
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 512	return page;
 
 513stale:
 514	rcu_read_unlock();
 
 
 
 
 
 
 
 
 515	remove_node_from_stable_tree(stable_node);
 516	return NULL;
 517}
 518
 519/*
 520 * Removing rmap_item from stable or unstable tree.
 521 * This function will clean the information from the stable/unstable tree.
 522 */
 523static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
 524{
 525	if (rmap_item->address & STABLE_FLAG) {
 526		struct stable_node *stable_node;
 527		struct page *page;
 528
 529		stable_node = rmap_item->head;
 530		page = get_ksm_page(stable_node);
 531		if (!page)
 532			goto out;
 533
 534		lock_page(page);
 535		hlist_del(&rmap_item->hlist);
 536		unlock_page(page);
 537		put_page(page);
 538
 539		if (stable_node->hlist.first)
 540			ksm_pages_sharing--;
 541		else
 542			ksm_pages_shared--;
 543
 
 
 
 
 
 544		put_anon_vma(rmap_item->anon_vma);
 
 545		rmap_item->address &= PAGE_MASK;
 546
 547	} else if (rmap_item->address & UNSTABLE_FLAG) {
 548		unsigned char age;
 549		/*
 550		 * Usually ksmd can and must skip the rb_erase, because
 551		 * root_unstable_tree was already reset to RB_ROOT.
 552		 * But be careful when an mm is exiting: do the rb_erase
 553		 * if this rmap_item was inserted by this scan, rather
 554		 * than left over from before.
 555		 */
 556		age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
 557		BUG_ON(age > 1);
 558		if (!age)
 559			rb_erase(&rmap_item->node, &root_unstable_tree);
 560
 561		ksm_pages_unshared--;
 562		rmap_item->address &= PAGE_MASK;
 563	}
 564out:
 565	cond_resched();		/* we're called from many long loops */
 566}
 567
 568static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
 569				       struct rmap_item **rmap_list)
 570{
 571	while (*rmap_list) {
 572		struct rmap_item *rmap_item = *rmap_list;
 573		*rmap_list = rmap_item->rmap_list;
 574		remove_rmap_item_from_tree(rmap_item);
 575		free_rmap_item(rmap_item);
 576	}
 577}
 578
 579/*
 580 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
 581 * than check every pte of a given vma, the locking doesn't quite work for
 582 * that - an rmap_item is assigned to the stable tree after inserting ksm
 583 * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
 584 * rmap_items from parent to child at fork time (so as not to waste time
 585 * if exit comes before the next scan reaches it).
 586 *
 587 * Similarly, although we'd like to remove rmap_items (so updating counts
 588 * and freeing memory) when unmerging an area, it's easier to leave that
 589 * to the next pass of ksmd - consider, for example, how ksmd might be
 590 * in cmp_and_merge_page on one of the rmap_items we would be removing.
 591 */
 592static int unmerge_ksm_pages(struct vm_area_struct *vma,
 593			     unsigned long start, unsigned long end)
 594{
 595	unsigned long addr;
 596	int err = 0;
 597
 598	for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
 599		if (ksm_test_exit(vma->vm_mm))
 600			break;
 601		if (signal_pending(current))
 602			err = -ERESTARTSYS;
 603		else
 604			err = break_ksm(vma, addr);
 605	}
 606	return err;
 607}
 608
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 609#ifdef CONFIG_SYSFS
 610/*
 611 * Only called through the sysfs control interface:
 612 */
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 613static int unmerge_and_remove_all_rmap_items(void)
 614{
 615	struct mm_slot *mm_slot;
 
 616	struct mm_struct *mm;
 617	struct vm_area_struct *vma;
 618	int err = 0;
 619
 620	spin_lock(&ksm_mmlist_lock);
 621	ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
 622						struct mm_slot, mm_list);
 
 623	spin_unlock(&ksm_mmlist_lock);
 624
 625	for (mm_slot = ksm_scan.mm_slot;
 626			mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
 627		mm = mm_slot->mm;
 628		down_read(&mm->mmap_sem);
 629		for (vma = mm->mmap; vma; vma = vma->vm_next) {
 630			if (ksm_test_exit(mm))
 631				break;
 
 
 
 
 
 
 
 
 632			if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 633				continue;
 634			err = unmerge_ksm_pages(vma,
 635						vma->vm_start, vma->vm_end);
 636			if (err)
 637				goto error;
 638		}
 639
 640		remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
 
 
 641
 642		spin_lock(&ksm_mmlist_lock);
 643		ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
 644						struct mm_slot, mm_list);
 
 645		if (ksm_test_exit(mm)) {
 646			hlist_del(&mm_slot->link);
 647			list_del(&mm_slot->mm_list);
 648			spin_unlock(&ksm_mmlist_lock);
 649
 650			free_mm_slot(mm_slot);
 651			clear_bit(MMF_VM_MERGEABLE, &mm->flags);
 652			up_read(&mm->mmap_sem);
 653			mmdrop(mm);
 654		} else {
 655			spin_unlock(&ksm_mmlist_lock);
 656			up_read(&mm->mmap_sem);
 657		}
 658	}
 659
 
 
 660	ksm_scan.seqnr = 0;
 661	return 0;
 662
 663error:
 664	up_read(&mm->mmap_sem);
 665	spin_lock(&ksm_mmlist_lock);
 666	ksm_scan.mm_slot = &ksm_mm_head;
 667	spin_unlock(&ksm_mmlist_lock);
 668	return err;
 669}
 670#endif /* CONFIG_SYSFS */
 671
 672static u32 calc_checksum(struct page *page)
 673{
 674	u32 checksum;
 675	void *addr = kmap_atomic(page, KM_USER0);
 676	checksum = jhash2(addr, PAGE_SIZE / 4, 17);
 677	kunmap_atomic(addr, KM_USER0);
 678	return checksum;
 679}
 680
 681static int memcmp_pages(struct page *page1, struct page *page2)
 682{
 683	char *addr1, *addr2;
 684	int ret;
 685
 686	addr1 = kmap_atomic(page1, KM_USER0);
 687	addr2 = kmap_atomic(page2, KM_USER1);
 688	ret = memcmp(addr1, addr2, PAGE_SIZE);
 689	kunmap_atomic(addr2, KM_USER1);
 690	kunmap_atomic(addr1, KM_USER0);
 691	return ret;
 692}
 693
 694static inline int pages_identical(struct page *page1, struct page *page2)
 695{
 696	return !memcmp_pages(page1, page2);
 697}
 698
 699static int write_protect_page(struct vm_area_struct *vma, struct page *page,
 700			      pte_t *orig_pte)
 701{
 702	struct mm_struct *mm = vma->vm_mm;
 703	unsigned long addr;
 704	pte_t *ptep;
 705	spinlock_t *ptl;
 706	int swapped;
 707	int err = -EFAULT;
 
 
 
 708
 709	addr = page_address_in_vma(page, vma);
 710	if (addr == -EFAULT)
 711		goto out;
 712
 713	BUG_ON(PageTransCompound(page));
 714	ptep = page_check_address(page, mm, addr, &ptl, 0);
 715	if (!ptep)
 716		goto out;
 717
 718	if (pte_write(*ptep) || pte_dirty(*ptep)) {
 719		pte_t entry;
 720
 
 
 
 
 
 
 
 
 
 
 
 
 
 721		swapped = PageSwapCache(page);
 722		flush_cache_page(vma, addr, page_to_pfn(page));
 723		/*
 724		 * Ok this is tricky, when get_user_pages_fast() run it doesn't
 725		 * take any lock, therefore the check that we are going to make
 726		 * with the pagecount against the mapcount is racey and
 727		 * O_DIRECT can happen right after the check.
 728		 * So we clear the pte and flush the tlb before the check
 729		 * this assure us that no O_DIRECT can happen after the check
 730		 * or in the middle of the check.
 
 
 
 
 
 731		 */
 732		entry = ptep_clear_flush(vma, addr, ptep);
 733		/*
 734		 * Check that no O_DIRECT or similar I/O is in progress on the
 735		 * page
 736		 */
 737		if (page_mapcount(page) + 1 + swapped != page_count(page)) {
 738			set_pte_at(mm, addr, ptep, entry);
 
 
 
 
 
 
 
 739			goto out_unlock;
 740		}
 
 741		if (pte_dirty(entry))
 742			set_page_dirty(page);
 743		entry = pte_mkclean(pte_wrprotect(entry));
 744		set_pte_at_notify(mm, addr, ptep, entry);
 
 
 
 
 745	}
 746	*orig_pte = *ptep;
 747	err = 0;
 748
 749out_unlock:
 750	pte_unmap_unlock(ptep, ptl);
 
 
 751out:
 752	return err;
 753}
 754
 755/**
 756 * replace_page - replace page in vma by new ksm page
 757 * @vma:      vma that holds the pte pointing to page
 758 * @page:     the page we are replacing by kpage
 759 * @kpage:    the ksm page we replace page by
 760 * @orig_pte: the original value of the pte
 761 *
 762 * Returns 0 on success, -EFAULT on failure.
 763 */
 764static int replace_page(struct vm_area_struct *vma, struct page *page,
 765			struct page *kpage, pte_t orig_pte)
 766{
 
 767	struct mm_struct *mm = vma->vm_mm;
 768	pgd_t *pgd;
 769	pud_t *pud;
 770	pmd_t *pmd;
 
 771	pte_t *ptep;
 
 772	spinlock_t *ptl;
 773	unsigned long addr;
 774	int err = -EFAULT;
 
 775
 776	addr = page_address_in_vma(page, vma);
 777	if (addr == -EFAULT)
 778		goto out;
 779
 780	pgd = pgd_offset(mm, addr);
 781	if (!pgd_present(*pgd))
 782		goto out;
 783
 784	pud = pud_offset(pgd, addr);
 785	if (!pud_present(*pud))
 
 
 
 
 786		goto out;
 787
 788	pmd = pmd_offset(pud, addr);
 789	BUG_ON(pmd_trans_huge(*pmd));
 790	if (!pmd_present(*pmd))
 791		goto out;
 792
 793	ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
 794	if (!pte_same(*ptep, orig_pte)) {
 
 
 795		pte_unmap_unlock(ptep, ptl);
 796		goto out;
 797	}
 
 
 
 798
 799	get_page(kpage);
 800	page_add_anon_rmap(kpage, vma, addr);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 801
 802	flush_cache_page(vma, addr, pte_pfn(*ptep));
 
 
 
 
 
 
 803	ptep_clear_flush(vma, addr, ptep);
 804	set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
 805
 806	page_remove_rmap(page);
 807	if (!page_mapped(page))
 808		try_to_free_swap(page);
 809	put_page(page);
 
 810
 811	pte_unmap_unlock(ptep, ptl);
 812	err = 0;
 
 
 813out:
 814	return err;
 815}
 816
 817static int page_trans_compound_anon_split(struct page *page)
 818{
 819	int ret = 0;
 820	struct page *transhuge_head = page_trans_compound_anon(page);
 821	if (transhuge_head) {
 822		/* Get the reference on the head to split it. */
 823		if (get_page_unless_zero(transhuge_head)) {
 824			/*
 825			 * Recheck we got the reference while the head
 826			 * was still anonymous.
 827			 */
 828			if (PageAnon(transhuge_head))
 829				ret = split_huge_page(transhuge_head);
 830			else
 831				/*
 832				 * Retry later if split_huge_page run
 833				 * from under us.
 834				 */
 835				ret = 1;
 836			put_page(transhuge_head);
 837		} else
 838			/* Retry later if split_huge_page run from under us. */
 839			ret = 1;
 840	}
 841	return ret;
 842}
 843
 844/*
 845 * try_to_merge_one_page - take two pages and merge them into one
 846 * @vma: the vma that holds the pte pointing to page
 847 * @page: the PageAnon page that we want to replace with kpage
 848 * @kpage: the PageKsm page that we want to map instead of page,
 849 *         or NULL the first time when we want to use page as kpage.
 850 *
 851 * This function returns 0 if the pages were merged, -EFAULT otherwise.
 852 */
 853static int try_to_merge_one_page(struct vm_area_struct *vma,
 854				 struct page *page, struct page *kpage)
 855{
 856	pte_t orig_pte = __pte(0);
 857	int err = -EFAULT;
 858
 859	if (page == kpage)			/* ksm page forked */
 860		return 0;
 861
 862	if (!(vma->vm_flags & VM_MERGEABLE))
 863		goto out;
 864	if (PageTransCompound(page) && page_trans_compound_anon_split(page))
 865		goto out;
 866	BUG_ON(PageTransCompound(page));
 867	if (!PageAnon(page))
 868		goto out;
 869
 870	/*
 871	 * We need the page lock to read a stable PageSwapCache in
 872	 * write_protect_page().  We use trylock_page() instead of
 873	 * lock_page() because we don't want to wait here - we
 874	 * prefer to continue scanning and merging different pages,
 875	 * then come back to this page when it is unlocked.
 876	 */
 877	if (!trylock_page(page))
 878		goto out;
 
 
 
 
 
 
 879	/*
 880	 * If this anonymous page is mapped only here, its pte may need
 881	 * to be write-protected.  If it's mapped elsewhere, all of its
 882	 * ptes are necessarily already write-protected.  But in either
 883	 * case, we need to lock and check page_count is not raised.
 884	 */
 885	if (write_protect_page(vma, page, &orig_pte) == 0) {
 886		if (!kpage) {
 887			/*
 888			 * While we hold page lock, upgrade page from
 889			 * PageAnon+anon_vma to PageKsm+NULL stable_node:
 890			 * stable_tree_insert() will update stable_node.
 891			 */
 892			set_page_stable_node(page, NULL);
 893			mark_page_accessed(page);
 
 
 
 
 
 
 894			err = 0;
 895		} else if (pages_identical(page, kpage))
 896			err = replace_page(vma, page, kpage, orig_pte);
 897	}
 898
 899	if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
 900		munlock_vma_page(page);
 901		if (!PageMlocked(kpage)) {
 902			unlock_page(page);
 903			lock_page(kpage);
 904			mlock_vma_page(kpage);
 905			page = kpage;		/* for final unlock */
 906		}
 907	}
 908
 909	unlock_page(page);
 910out:
 911	return err;
 912}
 913
 914/*
 915 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
 916 * but no new kernel page is allocated: kpage must already be a ksm page.
 917 *
 918 * This function returns 0 if the pages were merged, -EFAULT otherwise.
 919 */
 920static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
 921				      struct page *page, struct page *kpage)
 922{
 923	struct mm_struct *mm = rmap_item->mm;
 924	struct vm_area_struct *vma;
 925	int err = -EFAULT;
 926
 927	down_read(&mm->mmap_sem);
 928	if (ksm_test_exit(mm))
 929		goto out;
 930	vma = find_vma(mm, rmap_item->address);
 931	if (!vma || vma->vm_start > rmap_item->address)
 932		goto out;
 933
 934	err = try_to_merge_one_page(vma, page, kpage);
 935	if (err)
 936		goto out;
 937
 938	/* Must get reference to anon_vma while still holding mmap_sem */
 
 
 
 939	rmap_item->anon_vma = vma->anon_vma;
 940	get_anon_vma(vma->anon_vma);
 941out:
 942	up_read(&mm->mmap_sem);
 
 
 943	return err;
 944}
 945
 946/*
 947 * try_to_merge_two_pages - take two identical pages and prepare them
 948 * to be merged into one page.
 949 *
 950 * This function returns the kpage if we successfully merged two identical
 951 * pages into one ksm page, NULL otherwise.
 952 *
 953 * Note that this function upgrades page to ksm page: if one of the pages
 954 * is already a ksm page, try_to_merge_with_ksm_page should be used.
 955 */
 956static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
 957					   struct page *page,
 958					   struct rmap_item *tree_rmap_item,
 959					   struct page *tree_page)
 960{
 961	int err;
 962
 963	err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
 964	if (!err) {
 965		err = try_to_merge_with_ksm_page(tree_rmap_item,
 966							tree_page, page);
 967		/*
 968		 * If that fails, we have a ksm page with only one pte
 969		 * pointing to it: so break it.
 970		 */
 971		if (err)
 972			break_cow(rmap_item);
 973	}
 974	return err ? NULL : page;
 975}
 976
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 977/*
 978 * stable_tree_search - search for page inside the stable tree
 979 *
 980 * This function checks if there is a page inside the stable tree
 981 * with identical content to the page that we are scanning right now.
 982 *
 983 * This function returns the stable tree node of identical content if found,
 984 * NULL otherwise.
 985 */
 986static struct page *stable_tree_search(struct page *page)
 987{
 988	struct rb_node *node = root_stable_tree.rb_node;
 989	struct stable_node *stable_node;
 990
 991	stable_node = page_stable_node(page);
 992	if (stable_node) {			/* ksm page forked */
 
 
 
 
 
 993		get_page(page);
 994		return page;
 995	}
 996
 997	while (node) {
 
 
 
 
 
 
 998		struct page *tree_page;
 999		int ret;
1000
1001		cond_resched();
1002		stable_node = rb_entry(node, struct stable_node, node);
1003		tree_page = get_ksm_page(stable_node);
1004		if (!tree_page)
1005			return NULL;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1006
1007		ret = memcmp_pages(page, tree_page);
 
1008
1009		if (ret < 0) {
1010			put_page(tree_page);
1011			node = node->rb_left;
1012		} else if (ret > 0) {
1013			put_page(tree_page);
1014			node = node->rb_right;
1015		} else
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1016			return tree_page;
 
1017	}
1018
1019	return NULL;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1020}
1021
1022/*
1023 * stable_tree_insert - insert rmap_item pointing to new ksm page
1024 * into the stable tree.
1025 *
1026 * This function returns the stable tree node just allocated on success,
1027 * NULL otherwise.
1028 */
1029static struct stable_node *stable_tree_insert(struct page *kpage)
1030{
1031	struct rb_node **new = &root_stable_tree.rb_node;
1032	struct rb_node *parent = NULL;
1033	struct stable_node *stable_node;
 
 
 
 
 
 
 
 
 
 
 
1034
1035	while (*new) {
1036		struct page *tree_page;
1037		int ret;
1038
1039		cond_resched();
1040		stable_node = rb_entry(*new, struct stable_node, node);
1041		tree_page = get_ksm_page(stable_node);
1042		if (!tree_page)
1043			return NULL;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1044
1045		ret = memcmp_pages(kpage, tree_page);
1046		put_page(tree_page);
1047
1048		parent = *new;
1049		if (ret < 0)
1050			new = &parent->rb_left;
1051		else if (ret > 0)
1052			new = &parent->rb_right;
1053		else {
1054			/*
1055			 * It is not a bug that stable_tree_search() didn't
1056			 * find this node: because at that time our page was
1057			 * not yet write-protected, so may have changed since.
1058			 */
1059			return NULL;
1060		}
1061	}
1062
1063	stable_node = alloc_stable_node();
1064	if (!stable_node)
1065		return NULL;
1066
1067	rb_link_node(&stable_node->node, parent, new);
1068	rb_insert_color(&stable_node->node, &root_stable_tree);
1069
1070	INIT_HLIST_HEAD(&stable_node->hlist);
1071
1072	stable_node->kpfn = page_to_pfn(kpage);
1073	set_page_stable_node(kpage, stable_node);
 
 
 
 
 
 
 
 
 
 
 
 
 
1074
1075	return stable_node;
1076}
1077
1078/*
1079 * unstable_tree_search_insert - search for identical page,
1080 * else insert rmap_item into the unstable tree.
1081 *
1082 * This function searches for a page in the unstable tree identical to the
1083 * page currently being scanned; and if no identical page is found in the
1084 * tree, we insert rmap_item as a new object into the unstable tree.
1085 *
1086 * This function returns pointer to rmap_item found to be identical
1087 * to the currently scanned page, NULL otherwise.
1088 *
1089 * This function does both searching and inserting, because they share
1090 * the same walking algorithm in an rbtree.
1091 */
1092static
1093struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1094					      struct page *page,
1095					      struct page **tree_pagep)
1096
1097{
1098	struct rb_node **new = &root_unstable_tree.rb_node;
 
1099	struct rb_node *parent = NULL;
 
 
 
 
 
1100
1101	while (*new) {
1102		struct rmap_item *tree_rmap_item;
1103		struct page *tree_page;
1104		int ret;
1105
1106		cond_resched();
1107		tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1108		tree_page = get_mergeable_page(tree_rmap_item);
1109		if (IS_ERR_OR_NULL(tree_page))
1110			return NULL;
1111
1112		/*
1113		 * Don't substitute a ksm page for a forked page.
1114		 */
1115		if (page == tree_page) {
1116			put_page(tree_page);
1117			return NULL;
1118		}
1119
1120		ret = memcmp_pages(page, tree_page);
1121
1122		parent = *new;
1123		if (ret < 0) {
1124			put_page(tree_page);
1125			new = &parent->rb_left;
1126		} else if (ret > 0) {
1127			put_page(tree_page);
1128			new = &parent->rb_right;
 
 
 
 
 
 
 
 
 
1129		} else {
1130			*tree_pagep = tree_page;
1131			return tree_rmap_item;
1132		}
1133	}
1134
1135	rmap_item->address |= UNSTABLE_FLAG;
1136	rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
 
1137	rb_link_node(&rmap_item->node, parent, new);
1138	rb_insert_color(&rmap_item->node, &root_unstable_tree);
1139
1140	ksm_pages_unshared++;
1141	return NULL;
1142}
1143
1144/*
1145 * stable_tree_append - add another rmap_item to the linked list of
1146 * rmap_items hanging off a given node of the stable tree, all sharing
1147 * the same ksm page.
1148 */
1149static void stable_tree_append(struct rmap_item *rmap_item,
1150			       struct stable_node *stable_node)
 
1151{
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1152	rmap_item->head = stable_node;
1153	rmap_item->address |= STABLE_FLAG;
1154	hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1155
1156	if (rmap_item->hlist.next)
1157		ksm_pages_sharing++;
1158	else
1159		ksm_pages_shared++;
 
 
1160}
1161
1162/*
1163 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1164 * if not, compare checksum to previous and if it's the same, see if page can
1165 * be inserted into the unstable tree, or merged with a page already there and
1166 * both transferred to the stable tree.
1167 *
1168 * @page: the page that we are searching identical page to.
1169 * @rmap_item: the reverse mapping into the virtual address of this page
1170 */
1171static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1172{
1173	struct rmap_item *tree_rmap_item;
 
1174	struct page *tree_page = NULL;
1175	struct stable_node *stable_node;
1176	struct page *kpage;
1177	unsigned int checksum;
1178	int err;
 
1179
1180	remove_rmap_item_from_tree(rmap_item);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1181
1182	/* We first start with searching the page inside the stable tree */
1183	kpage = stable_tree_search(page);
 
 
 
 
 
 
 
1184	if (kpage) {
 
 
 
1185		err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1186		if (!err) {
1187			/*
1188			 * The page was successfully merged:
1189			 * add its rmap_item to the stable tree.
1190			 */
1191			lock_page(kpage);
1192			stable_tree_append(rmap_item, page_stable_node(kpage));
 
1193			unlock_page(kpage);
1194		}
1195		put_page(kpage);
1196		return;
1197	}
1198
1199	/*
1200	 * If the hash value of the page has changed from the last time
1201	 * we calculated it, this page is changing frequently: therefore we
1202	 * don't want to insert it in the unstable tree, and we don't want
1203	 * to waste our time searching for something identical to it there.
1204	 */
1205	checksum = calc_checksum(page);
1206	if (rmap_item->oldchecksum != checksum) {
1207		rmap_item->oldchecksum = checksum;
1208		return;
1209	}
1210
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1211	tree_rmap_item =
1212		unstable_tree_search_insert(rmap_item, page, &tree_page);
1213	if (tree_rmap_item) {
 
 
1214		kpage = try_to_merge_two_pages(rmap_item, page,
1215						tree_rmap_item, tree_page);
1216		put_page(tree_page);
1217		/*
1218		 * As soon as we merge this page, we want to remove the
1219		 * rmap_item of the page we have merged with from the unstable
1220		 * tree, and insert it instead as new node in the stable tree.
 
 
 
 
 
1221		 */
 
 
 
1222		if (kpage) {
1223			remove_rmap_item_from_tree(tree_rmap_item);
1224
 
 
1225			lock_page(kpage);
1226			stable_node = stable_tree_insert(kpage);
1227			if (stable_node) {
1228				stable_tree_append(tree_rmap_item, stable_node);
1229				stable_tree_append(rmap_item, stable_node);
 
 
1230			}
1231			unlock_page(kpage);
1232
1233			/*
1234			 * If we fail to insert the page into the stable tree,
1235			 * we will have 2 virtual addresses that are pointing
1236			 * to a ksm page left outside the stable tree,
1237			 * in which case we need to break_cow on both.
1238			 */
1239			if (!stable_node) {
1240				break_cow(tree_rmap_item);
1241				break_cow(rmap_item);
1242			}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1243		}
1244	}
1245}
1246
1247static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1248					    struct rmap_item **rmap_list,
1249					    unsigned long addr)
1250{
1251	struct rmap_item *rmap_item;
1252
1253	while (*rmap_list) {
1254		rmap_item = *rmap_list;
1255		if ((rmap_item->address & PAGE_MASK) == addr)
1256			return rmap_item;
1257		if (rmap_item->address > addr)
1258			break;
1259		*rmap_list = rmap_item->rmap_list;
1260		remove_rmap_item_from_tree(rmap_item);
1261		free_rmap_item(rmap_item);
1262	}
1263
1264	rmap_item = alloc_rmap_item();
1265	if (rmap_item) {
1266		/* It has already been zeroed */
1267		rmap_item->mm = mm_slot->mm;
 
1268		rmap_item->address = addr;
1269		rmap_item->rmap_list = *rmap_list;
1270		*rmap_list = rmap_item;
1271	}
1272	return rmap_item;
1273}
1274
1275static struct rmap_item *scan_get_next_rmap_item(struct page **page)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1276{
1277	struct mm_struct *mm;
 
1278	struct mm_slot *slot;
1279	struct vm_area_struct *vma;
1280	struct rmap_item *rmap_item;
 
 
1281
1282	if (list_empty(&ksm_mm_head.mm_list))
1283		return NULL;
1284
1285	slot = ksm_scan.mm_slot;
1286	if (slot == &ksm_mm_head) {
 
 
 
1287		/*
1288		 * A number of pages can hang around indefinitely on per-cpu
1289		 * pagevecs, raised page count preventing write_protect_page
1290		 * from merging them.  Though it doesn't really matter much,
1291		 * it is puzzling to see some stuck in pages_volatile until
1292		 * other activity jostles them out, and they also prevented
1293		 * LTP's KSM test from succeeding deterministically; so drain
1294		 * them here (here rather than on entry to ksm_do_scan(),
1295		 * so we don't IPI too often when pages_to_scan is set low).
1296		 */
1297		lru_add_drain_all();
1298
1299		root_unstable_tree = RB_ROOT;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1300
1301		spin_lock(&ksm_mmlist_lock);
1302		slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1303		ksm_scan.mm_slot = slot;
 
 
1304		spin_unlock(&ksm_mmlist_lock);
1305		/*
1306		 * Although we tested list_empty() above, a racing __ksm_exit
1307		 * of the last mm on the list may have removed it since then.
1308		 */
1309		if (slot == &ksm_mm_head)
1310			return NULL;
1311next_mm:
1312		ksm_scan.address = 0;
1313		ksm_scan.rmap_list = &slot->rmap_list;
1314	}
1315
 
1316	mm = slot->mm;
1317	down_read(&mm->mmap_sem);
 
 
1318	if (ksm_test_exit(mm))
1319		vma = NULL;
1320	else
1321		vma = find_vma(mm, ksm_scan.address);
1322
1323	for (; vma; vma = vma->vm_next) {
1324		if (!(vma->vm_flags & VM_MERGEABLE))
1325			continue;
1326		if (ksm_scan.address < vma->vm_start)
1327			ksm_scan.address = vma->vm_start;
1328		if (!vma->anon_vma)
1329			ksm_scan.address = vma->vm_end;
1330
1331		while (ksm_scan.address < vma->vm_end) {
1332			if (ksm_test_exit(mm))
1333				break;
1334			*page = follow_page(vma, ksm_scan.address, FOLL_GET);
1335			if (IS_ERR_OR_NULL(*page)) {
1336				ksm_scan.address += PAGE_SIZE;
1337				cond_resched();
1338				continue;
1339			}
1340			if (PageAnon(*page) ||
1341			    page_trans_compound_anon(*page)) {
 
1342				flush_anon_page(vma, *page, ksm_scan.address);
1343				flush_dcache_page(*page);
1344				rmap_item = get_next_rmap_item(slot,
1345					ksm_scan.rmap_list, ksm_scan.address);
1346				if (rmap_item) {
1347					ksm_scan.rmap_list =
1348							&rmap_item->rmap_list;
 
 
 
 
1349					ksm_scan.address += PAGE_SIZE;
1350				} else
1351					put_page(*page);
1352				up_read(&mm->mmap_sem);
1353				return rmap_item;
1354			}
 
1355			put_page(*page);
1356			ksm_scan.address += PAGE_SIZE;
1357			cond_resched();
1358		}
1359	}
1360
1361	if (ksm_test_exit(mm)) {
 
1362		ksm_scan.address = 0;
1363		ksm_scan.rmap_list = &slot->rmap_list;
1364	}
1365	/*
1366	 * Nuke all the rmap_items that are above this current rmap:
1367	 * because there were no VM_MERGEABLE vmas with such addresses.
1368	 */
1369	remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1370
1371	spin_lock(&ksm_mmlist_lock);
1372	ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1373						struct mm_slot, mm_list);
 
1374	if (ksm_scan.address == 0) {
1375		/*
1376		 * We've completed a full scan of all vmas, holding mmap_sem
1377		 * throughout, and found no VM_MERGEABLE: so do the same as
1378		 * __ksm_exit does to remove this mm from all our lists now.
1379		 * This applies either when cleaning up after __ksm_exit
1380		 * (but beware: we can reach here even before __ksm_exit),
1381		 * or when all VM_MERGEABLE areas have been unmapped (and
1382		 * mmap_sem then protects against race with MADV_MERGEABLE).
1383		 */
1384		hlist_del(&slot->link);
1385		list_del(&slot->mm_list);
1386		spin_unlock(&ksm_mmlist_lock);
1387
1388		free_mm_slot(slot);
1389		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1390		up_read(&mm->mmap_sem);
 
1391		mmdrop(mm);
1392	} else {
 
 
 
 
 
 
 
 
1393		spin_unlock(&ksm_mmlist_lock);
1394		up_read(&mm->mmap_sem);
1395	}
1396
1397	/* Repeat until we've completed scanning the whole list */
1398	slot = ksm_scan.mm_slot;
1399	if (slot != &ksm_mm_head)
1400		goto next_mm;
1401
 
 
 
1402	ksm_scan.seqnr++;
1403	return NULL;
1404}
1405
1406/**
1407 * ksm_do_scan  - the ksm scanner main worker function.
1408 * @scan_npages - number of pages we want to scan before we return.
1409 */
1410static void ksm_do_scan(unsigned int scan_npages)
1411{
1412	struct rmap_item *rmap_item;
1413	struct page *uninitialized_var(page);
 
1414
1415	while (scan_npages-- && likely(!freezing(current))) {
1416		cond_resched();
1417		rmap_item = scan_get_next_rmap_item(&page);
1418		if (!rmap_item)
1419			return;
1420		if (!PageKsm(page) || !in_stable_tree(rmap_item))
1421			cmp_and_merge_page(page, rmap_item);
1422		put_page(page);
1423	}
 
 
1424}
1425
1426static int ksmd_should_run(void)
1427{
1428	return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1429}
1430
1431static int ksm_scan_thread(void *nothing)
1432{
 
 
1433	set_freezable();
1434	set_user_nice(current, 5);
1435
1436	while (!kthread_should_stop()) {
1437		mutex_lock(&ksm_thread_mutex);
 
1438		if (ksmd_should_run())
1439			ksm_do_scan(ksm_thread_pages_to_scan);
1440		mutex_unlock(&ksm_thread_mutex);
1441
1442		try_to_freeze();
1443
1444		if (ksmd_should_run()) {
1445			schedule_timeout_interruptible(
1446				msecs_to_jiffies(ksm_thread_sleep_millisecs));
 
 
1447		} else {
1448			wait_event_freezable(ksm_thread_wait,
1449				ksmd_should_run() || kthread_should_stop());
1450		}
1451	}
1452	return 0;
1453}
1454
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1455int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1456		unsigned long end, int advice, unsigned long *vm_flags)
1457{
1458	struct mm_struct *mm = vma->vm_mm;
1459	int err;
1460
1461	switch (advice) {
1462	case MADV_MERGEABLE:
1463		/*
1464		 * Be somewhat over-protective for now!
1465		 */
1466		if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1467				 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1468				 VM_RESERVED  | VM_HUGETLB | VM_INSERTPAGE |
1469				 VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1470			return 0;		/* just ignore the advice */
1471
1472		if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1473			err = __ksm_enter(mm);
1474			if (err)
1475				return err;
1476		}
1477
1478		*vm_flags |= VM_MERGEABLE;
1479		break;
1480
1481	case MADV_UNMERGEABLE:
1482		if (!(*vm_flags & VM_MERGEABLE))
1483			return 0;		/* just ignore the advice */
1484
1485		if (vma->anon_vma) {
1486			err = unmerge_ksm_pages(vma, start, end);
1487			if (err)
1488				return err;
1489		}
1490
1491		*vm_flags &= ~VM_MERGEABLE;
1492		break;
1493	}
1494
1495	return 0;
1496}
 
1497
1498int __ksm_enter(struct mm_struct *mm)
1499{
1500	struct mm_slot *mm_slot;
 
1501	int needs_wakeup;
1502
1503	mm_slot = alloc_mm_slot();
1504	if (!mm_slot)
1505		return -ENOMEM;
1506
 
 
1507	/* Check ksm_run too?  Would need tighter locking */
1508	needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1509
1510	spin_lock(&ksm_mmlist_lock);
1511	insert_to_mm_slots_hash(mm, mm_slot);
1512	/*
1513	 * Insert just behind the scanning cursor, to let the area settle
 
1514	 * down a little; when fork is followed by immediate exec, we don't
1515	 * want ksmd to waste time setting up and tearing down an rmap_list.
 
 
 
 
1516	 */
1517	list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
 
 
 
1518	spin_unlock(&ksm_mmlist_lock);
1519
1520	set_bit(MMF_VM_MERGEABLE, &mm->flags);
1521	atomic_inc(&mm->mm_count);
1522
1523	if (needs_wakeup)
1524		wake_up_interruptible(&ksm_thread_wait);
1525
 
1526	return 0;
1527}
1528
1529void __ksm_exit(struct mm_struct *mm)
1530{
1531	struct mm_slot *mm_slot;
 
1532	int easy_to_free = 0;
1533
1534	/*
1535	 * This process is exiting: if it's straightforward (as is the
1536	 * case when ksmd was never running), free mm_slot immediately.
1537	 * But if it's at the cursor or has rmap_items linked to it, use
1538	 * mmap_sem to synchronize with any break_cows before pagetables
1539	 * are freed, and leave the mm_slot on the list for ksmd to free.
1540	 * Beware: ksm may already have noticed it exiting and freed the slot.
1541	 */
1542
1543	spin_lock(&ksm_mmlist_lock);
1544	mm_slot = get_mm_slot(mm);
 
1545	if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1546		if (!mm_slot->rmap_list) {
1547			hlist_del(&mm_slot->link);
1548			list_del(&mm_slot->mm_list);
1549			easy_to_free = 1;
1550		} else {
1551			list_move(&mm_slot->mm_list,
1552				  &ksm_scan.mm_slot->mm_list);
1553		}
1554	}
1555	spin_unlock(&ksm_mmlist_lock);
1556
1557	if (easy_to_free) {
1558		free_mm_slot(mm_slot);
 
1559		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1560		mmdrop(mm);
1561	} else if (mm_slot) {
1562		down_write(&mm->mmap_sem);
1563		up_write(&mm->mmap_sem);
1564	}
1565}
1566
1567struct page *ksm_does_need_to_copy(struct page *page,
1568			struct vm_area_struct *vma, unsigned long address)
1569{
1570	struct page *new_page;
1571
1572	new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1573	if (new_page) {
1574		copy_user_highpage(new_page, page, address, vma);
1575
1576		SetPageDirty(new_page);
1577		__SetPageUptodate(new_page);
1578		SetPageSwapBacked(new_page);
1579		__set_page_locked(new_page);
1580
1581		if (page_evictable(new_page, vma))
1582			lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1583		else
1584			add_page_to_unevictable_list(new_page);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1585	}
1586
1587	return new_page;
1588}
1589
1590int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1591			unsigned long *vm_flags)
1592{
1593	struct stable_node *stable_node;
1594	struct rmap_item *rmap_item;
1595	struct hlist_node *hlist;
1596	unsigned int mapcount = page_mapcount(page);
1597	int referenced = 0;
1598	int search_new_forks = 0;
1599
1600	VM_BUG_ON(!PageKsm(page));
1601	VM_BUG_ON(!PageLocked(page));
1602
1603	stable_node = page_stable_node(page);
 
 
 
 
 
 
1604	if (!stable_node)
1605		return 0;
1606again:
1607	hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1608		struct anon_vma *anon_vma = rmap_item->anon_vma;
1609		struct anon_vma_chain *vmac;
1610		struct vm_area_struct *vma;
1611
1612		anon_vma_lock(anon_vma);
1613		list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
 
 
 
 
 
 
 
 
 
 
 
1614			vma = vmac->vma;
1615			if (rmap_item->address < vma->vm_start ||
1616			    rmap_item->address >= vma->vm_end)
 
 
 
1617				continue;
1618			/*
1619			 * Initially we examine only the vma which covers this
1620			 * rmap_item; but later, if there is still work to do,
1621			 * we examine covering vmas in other mms: in case they
1622			 * were forked from the original since ksmd passed.
1623			 */
1624			if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1625				continue;
1626
1627			if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1628				continue;
1629
1630			referenced += page_referenced_one(page, vma,
1631				rmap_item->address, &mapcount, vm_flags);
1632			if (!search_new_forks || !mapcount)
1633				break;
 
 
 
 
1634		}
1635		anon_vma_unlock(anon_vma);
1636		if (!mapcount)
1637			goto out;
1638	}
1639	if (!search_new_forks++)
1640		goto again;
1641out:
1642	return referenced;
1643}
1644
1645int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
 
 
 
 
 
1646{
1647	struct stable_node *stable_node;
1648	struct hlist_node *hlist;
1649	struct rmap_item *rmap_item;
1650	int ret = SWAP_AGAIN;
1651	int search_new_forks = 0;
1652
1653	VM_BUG_ON(!PageKsm(page));
1654	VM_BUG_ON(!PageLocked(page));
1655
1656	stable_node = page_stable_node(page);
1657	if (!stable_node)
1658		return SWAP_FAIL;
1659again:
1660	hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1661		struct anon_vma *anon_vma = rmap_item->anon_vma;
1662		struct anon_vma_chain *vmac;
1663		struct vm_area_struct *vma;
1664
1665		anon_vma_lock(anon_vma);
1666		list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1667			vma = vmac->vma;
1668			if (rmap_item->address < vma->vm_start ||
1669			    rmap_item->address >= vma->vm_end)
 
 
 
1670				continue;
1671			/*
1672			 * Initially we examine only the vma which covers this
1673			 * rmap_item; but later, if there is still work to do,
1674			 * we examine covering vmas in other mms: in case they
1675			 * were forked from the original since ksmd passed.
1676			 */
1677			if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1678				continue;
1679
1680			ret = try_to_unmap_one(page, vma,
1681					rmap_item->address, flags);
1682			if (ret != SWAP_AGAIN || !page_mapped(page)) {
1683				anon_vma_unlock(anon_vma);
1684				goto out;
1685			}
1686		}
1687		anon_vma_unlock(anon_vma);
 
1688	}
1689	if (!search_new_forks++)
1690		goto again;
1691out:
1692	return ret;
1693}
 
1694
1695#ifdef CONFIG_MIGRATION
1696int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1697		  struct vm_area_struct *, unsigned long, void *), void *arg)
1698{
1699	struct stable_node *stable_node;
1700	struct hlist_node *hlist;
1701	struct rmap_item *rmap_item;
1702	int ret = SWAP_AGAIN;
1703	int search_new_forks = 0;
1704
1705	VM_BUG_ON(!PageKsm(page));
1706	VM_BUG_ON(!PageLocked(page));
 
1707
1708	stable_node = page_stable_node(page);
1709	if (!stable_node)
1710		return ret;
1711again:
1712	hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1713		struct anon_vma *anon_vma = rmap_item->anon_vma;
1714		struct anon_vma_chain *vmac;
1715		struct vm_area_struct *vma;
 
 
 
 
 
 
 
1716
1717		anon_vma_lock(anon_vma);
1718		list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1719			vma = vmac->vma;
1720			if (rmap_item->address < vma->vm_start ||
1721			    rmap_item->address >= vma->vm_end)
1722				continue;
1723			/*
1724			 * Initially we examine only the vma which covers this
1725			 * rmap_item; but later, if there is still work to do,
1726			 * we examine covering vmas in other mms: in case they
1727			 * were forked from the original since ksmd passed.
1728			 */
1729			if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1730				continue;
1731
1732			ret = rmap_one(page, vma, rmap_item->address, arg);
1733			if (ret != SWAP_AGAIN) {
1734				anon_vma_unlock(anon_vma);
1735				goto out;
1736			}
1737		}
1738		anon_vma_unlock(anon_vma);
 
 
 
 
 
1739	}
1740	if (!search_new_forks++)
1741		goto again;
1742out:
1743	return ret;
1744}
1745
1746void ksm_migrate_page(struct page *newpage, struct page *oldpage)
 
 
 
1747{
1748	struct stable_node *stable_node;
 
1749
1750	VM_BUG_ON(!PageLocked(oldpage));
1751	VM_BUG_ON(!PageLocked(newpage));
1752	VM_BUG_ON(newpage->mapping != oldpage->mapping);
 
 
1753
1754	stable_node = page_stable_node(newpage);
1755	if (stable_node) {
1756		VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1757		stable_node->kpfn = page_to_pfn(newpage);
1758	}
 
 
 
 
 
1759}
1760#endif /* CONFIG_MIGRATION */
1761
1762#ifdef CONFIG_MEMORY_HOTREMOVE
1763static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1764						 unsigned long end_pfn)
1765{
 
1766	struct rb_node *node;
 
1767
1768	for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1769		struct stable_node *stable_node;
1770
1771		stable_node = rb_entry(node, struct stable_node, node);
 
 
 
 
 
 
 
 
 
 
 
1772		if (stable_node->kpfn >= start_pfn &&
1773		    stable_node->kpfn < end_pfn)
1774			return stable_node;
 
1775	}
1776	return NULL;
1777}
1778
1779static int ksm_memory_callback(struct notifier_block *self,
1780			       unsigned long action, void *arg)
1781{
1782	struct memory_notify *mn = arg;
1783	struct stable_node *stable_node;
1784
1785	switch (action) {
1786	case MEM_GOING_OFFLINE:
1787		/*
1788		 * Keep it very simple for now: just lock out ksmd and
1789		 * MADV_UNMERGEABLE while any memory is going offline.
1790		 * mutex_lock_nested() is necessary because lockdep was alarmed
1791		 * that here we take ksm_thread_mutex inside notifier chain
1792		 * mutex, and later take notifier chain mutex inside
1793		 * ksm_thread_mutex to unlock it.   But that's safe because both
1794		 * are inside mem_hotplug_mutex.
1795		 */
1796		mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
 
 
1797		break;
1798
1799	case MEM_OFFLINE:
1800		/*
1801		 * Most of the work is done by page migration; but there might
1802		 * be a few stable_nodes left over, still pointing to struct
1803		 * pages which have been offlined: prune those from the tree.
 
 
1804		 */
1805		while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1806					mn->start_pfn + mn->nr_pages)) != NULL)
1807			remove_node_from_stable_tree(stable_node);
1808		/* fallthrough */
1809
1810	case MEM_CANCEL_OFFLINE:
 
 
1811		mutex_unlock(&ksm_thread_mutex);
 
 
 
1812		break;
1813	}
1814	return NOTIFY_OK;
1815}
 
 
 
 
1816#endif /* CONFIG_MEMORY_HOTREMOVE */
1817
 
 
 
 
 
 
 
 
1818#ifdef CONFIG_SYSFS
1819/*
1820 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1821 */
1822
1823#define KSM_ATTR_RO(_name) \
1824	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1825#define KSM_ATTR(_name) \
1826	static struct kobj_attribute _name##_attr = \
1827		__ATTR(_name, 0644, _name##_show, _name##_store)
1828
1829static ssize_t sleep_millisecs_show(struct kobject *kobj,
1830				    struct kobj_attribute *attr, char *buf)
1831{
1832	return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1833}
1834
1835static ssize_t sleep_millisecs_store(struct kobject *kobj,
1836				     struct kobj_attribute *attr,
1837				     const char *buf, size_t count)
1838{
1839	unsigned long msecs;
1840	int err;
1841
1842	err = strict_strtoul(buf, 10, &msecs);
1843	if (err || msecs > UINT_MAX)
1844		return -EINVAL;
1845
1846	ksm_thread_sleep_millisecs = msecs;
 
1847
1848	return count;
1849}
1850KSM_ATTR(sleep_millisecs);
1851
1852static ssize_t pages_to_scan_show(struct kobject *kobj,
1853				  struct kobj_attribute *attr, char *buf)
1854{
1855	return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1856}
1857
1858static ssize_t pages_to_scan_store(struct kobject *kobj,
1859				   struct kobj_attribute *attr,
1860				   const char *buf, size_t count)
1861{
 
1862	int err;
1863	unsigned long nr_pages;
1864
1865	err = strict_strtoul(buf, 10, &nr_pages);
1866	if (err || nr_pages > UINT_MAX)
 
 
 
1867		return -EINVAL;
1868
1869	ksm_thread_pages_to_scan = nr_pages;
1870
1871	return count;
1872}
1873KSM_ATTR(pages_to_scan);
1874
1875static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1876			char *buf)
1877{
1878	return sprintf(buf, "%u\n", ksm_run);
1879}
1880
1881static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1882			 const char *buf, size_t count)
1883{
 
1884	int err;
1885	unsigned long flags;
1886
1887	err = strict_strtoul(buf, 10, &flags);
1888	if (err || flags > UINT_MAX)
1889		return -EINVAL;
1890	if (flags > KSM_RUN_UNMERGE)
1891		return -EINVAL;
1892
1893	/*
1894	 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1895	 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1896	 * breaking COW to free the pages_shared (but leaves mm_slots
1897	 * on the list for when ksmd may be set running again).
1898	 */
1899
1900	mutex_lock(&ksm_thread_mutex);
 
1901	if (ksm_run != flags) {
1902		ksm_run = flags;
1903		if (flags & KSM_RUN_UNMERGE) {
1904			int oom_score_adj;
1905
1906			oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
1907			err = unmerge_and_remove_all_rmap_items();
1908			test_set_oom_score_adj(oom_score_adj);
1909			if (err) {
1910				ksm_run = KSM_RUN_STOP;
1911				count = err;
1912			}
1913		}
1914	}
1915	mutex_unlock(&ksm_thread_mutex);
1916
1917	if (flags & KSM_RUN_MERGE)
1918		wake_up_interruptible(&ksm_thread_wait);
1919
1920	return count;
1921}
1922KSM_ATTR(run);
1923
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1924static ssize_t pages_shared_show(struct kobject *kobj,
1925				 struct kobj_attribute *attr, char *buf)
1926{
1927	return sprintf(buf, "%lu\n", ksm_pages_shared);
1928}
1929KSM_ATTR_RO(pages_shared);
1930
1931static ssize_t pages_sharing_show(struct kobject *kobj,
1932				  struct kobj_attribute *attr, char *buf)
1933{
1934	return sprintf(buf, "%lu\n", ksm_pages_sharing);
1935}
1936KSM_ATTR_RO(pages_sharing);
1937
1938static ssize_t pages_unshared_show(struct kobject *kobj,
1939				   struct kobj_attribute *attr, char *buf)
1940{
1941	return sprintf(buf, "%lu\n", ksm_pages_unshared);
1942}
1943KSM_ATTR_RO(pages_unshared);
1944
1945static ssize_t pages_volatile_show(struct kobject *kobj,
1946				   struct kobj_attribute *attr, char *buf)
1947{
1948	long ksm_pages_volatile;
1949
1950	ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1951				- ksm_pages_sharing - ksm_pages_unshared;
1952	/*
1953	 * It was not worth any locking to calculate that statistic,
1954	 * but it might therefore sometimes be negative: conceal that.
1955	 */
1956	if (ksm_pages_volatile < 0)
1957		ksm_pages_volatile = 0;
1958	return sprintf(buf, "%ld\n", ksm_pages_volatile);
1959}
1960KSM_ATTR_RO(pages_volatile);
1961
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1962static ssize_t full_scans_show(struct kobject *kobj,
1963			       struct kobj_attribute *attr, char *buf)
1964{
1965	return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1966}
1967KSM_ATTR_RO(full_scans);
1968
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1969static struct attribute *ksm_attrs[] = {
1970	&sleep_millisecs_attr.attr,
1971	&pages_to_scan_attr.attr,
1972	&run_attr.attr,
 
1973	&pages_shared_attr.attr,
1974	&pages_sharing_attr.attr,
1975	&pages_unshared_attr.attr,
1976	&pages_volatile_attr.attr,
 
 
1977	&full_scans_attr.attr,
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1978	NULL,
1979};
1980
1981static struct attribute_group ksm_attr_group = {
1982	.attrs = ksm_attrs,
1983	.name = "ksm",
1984};
1985#endif /* CONFIG_SYSFS */
1986
1987static int __init ksm_init(void)
1988{
1989	struct task_struct *ksm_thread;
1990	int err;
1991
 
 
 
 
 
1992	err = ksm_slab_init();
1993	if (err)
1994		goto out;
1995
1996	ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1997	if (IS_ERR(ksm_thread)) {
1998		printk(KERN_ERR "ksm: creating kthread failed\n");
1999		err = PTR_ERR(ksm_thread);
2000		goto out_free;
2001	}
2002
2003#ifdef CONFIG_SYSFS
2004	err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2005	if (err) {
2006		printk(KERN_ERR "ksm: register sysfs failed\n");
2007		kthread_stop(ksm_thread);
2008		goto out_free;
2009	}
2010#else
2011	ksm_run = KSM_RUN_MERGE;	/* no way for user to start it */
2012
2013#endif /* CONFIG_SYSFS */
2014
2015#ifdef CONFIG_MEMORY_HOTREMOVE
2016	/*
2017	 * Choose a high priority since the callback takes ksm_thread_mutex:
2018	 * later callbacks could only be taking locks which nest within that.
2019	 */
2020	hotplug_memory_notifier(ksm_memory_callback, 100);
2021#endif
2022	return 0;
2023
2024out_free:
2025	ksm_slab_free();
2026out:
2027	return err;
2028}
2029module_init(ksm_init)
v6.8
   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * Memory merging support.
   4 *
   5 * This code enables dynamic sharing of identical pages found in different
   6 * memory areas, even if they are not shared by fork()
   7 *
   8 * Copyright (C) 2008-2009 Red Hat, Inc.
   9 * Authors:
  10 *	Izik Eidus
  11 *	Andrea Arcangeli
  12 *	Chris Wright
  13 *	Hugh Dickins
 
 
  14 */
  15
  16#include <linux/errno.h>
  17#include <linux/mm.h>
  18#include <linux/mm_inline.h>
  19#include <linux/fs.h>
  20#include <linux/mman.h>
  21#include <linux/sched.h>
  22#include <linux/sched/mm.h>
  23#include <linux/sched/coredump.h>
  24#include <linux/sched/cputime.h>
  25#include <linux/rwsem.h>
  26#include <linux/pagemap.h>
  27#include <linux/rmap.h>
  28#include <linux/spinlock.h>
  29#include <linux/xxhash.h>
  30#include <linux/delay.h>
  31#include <linux/kthread.h>
  32#include <linux/wait.h>
  33#include <linux/slab.h>
  34#include <linux/rbtree.h>
  35#include <linux/memory.h>
  36#include <linux/mmu_notifier.h>
  37#include <linux/swap.h>
  38#include <linux/ksm.h>
  39#include <linux/hashtable.h>
  40#include <linux/freezer.h>
  41#include <linux/oom.h>
  42#include <linux/numa.h>
  43#include <linux/pagewalk.h>
  44
  45#include <asm/tlbflush.h>
  46#include "internal.h"
  47#include "mm_slot.h"
  48
  49#define CREATE_TRACE_POINTS
  50#include <trace/events/ksm.h>
  51
  52#ifdef CONFIG_NUMA
  53#define NUMA(x)		(x)
  54#define DO_NUMA(x)	do { (x); } while (0)
  55#else
  56#define NUMA(x)		(0)
  57#define DO_NUMA(x)	do { } while (0)
  58#endif
  59
  60typedef u8 rmap_age_t;
  61
  62/**
  63 * DOC: Overview
  64 *
  65 * A few notes about the KSM scanning process,
  66 * to make it easier to understand the data structures below:
  67 *
  68 * In order to reduce excessive scanning, KSM sorts the memory pages by their
  69 * contents into a data structure that holds pointers to the pages' locations.
  70 *
  71 * Since the contents of the pages may change at any moment, KSM cannot just
  72 * insert the pages into a normal sorted tree and expect it to find anything.
  73 * Therefore KSM uses two data structures - the stable and the unstable tree.
  74 *
  75 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
  76 * by their contents.  Because each such page is write-protected, searching on
  77 * this tree is fully assured to be working (except when pages are unmapped),
  78 * and therefore this tree is called the stable tree.
  79 *
  80 * The stable tree node includes information required for reverse
  81 * mapping from a KSM page to virtual addresses that map this page.
  82 *
  83 * In order to avoid large latencies of the rmap walks on KSM pages,
  84 * KSM maintains two types of nodes in the stable tree:
  85 *
  86 * * the regular nodes that keep the reverse mapping structures in a
  87 *   linked list
  88 * * the "chains" that link nodes ("dups") that represent the same
  89 *   write protected memory content, but each "dup" corresponds to a
  90 *   different KSM page copy of that content
  91 *
  92 * Internally, the regular nodes, "dups" and "chains" are represented
  93 * using the same struct ksm_stable_node structure.
  94 *
  95 * In addition to the stable tree, KSM uses a second data structure called the
  96 * unstable tree: this tree holds pointers to pages which have been found to
  97 * be "unchanged for a period of time".  The unstable tree sorts these pages
  98 * by their contents, but since they are not write-protected, KSM cannot rely
  99 * upon the unstable tree to work correctly - the unstable tree is liable to
 100 * be corrupted as its contents are modified, and so it is called unstable.
 101 *
 102 * KSM solves this problem by several techniques:
 103 *
 104 * 1) The unstable tree is flushed every time KSM completes scanning all
 105 *    memory areas, and then the tree is rebuilt again from the beginning.
 106 * 2) KSM will only insert into the unstable tree, pages whose hash value
 107 *    has not changed since the previous scan of all memory areas.
 108 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
 109 *    colors of the nodes and not on their contents, assuring that even when
 110 *    the tree gets "corrupted" it won't get out of balance, so scanning time
 111 *    remains the same (also, searching and inserting nodes in an rbtree uses
 112 *    the same algorithm, so we have no overhead when we flush and rebuild).
 113 * 4) KSM never flushes the stable tree, which means that even if it were to
 114 *    take 10 attempts to find a page in the unstable tree, once it is found,
 115 *    it is secured in the stable tree.  (When we scan a new page, we first
 116 *    compare it against the stable tree, and then against the unstable tree.)
 117 *
 118 * If the merge_across_nodes tunable is unset, then KSM maintains multiple
 119 * stable trees and multiple unstable trees: one of each for each NUMA node.
 120 */
 121
 122/**
 123 * struct ksm_mm_slot - ksm information per mm that is being scanned
 124 * @slot: hash lookup from mm to mm_slot
 
 125 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
 
 126 */
 127struct ksm_mm_slot {
 128	struct mm_slot slot;
 129	struct ksm_rmap_item *rmap_list;
 
 
 130};
 131
 132/**
 133 * struct ksm_scan - cursor for scanning
 134 * @mm_slot: the current mm_slot we are scanning
 135 * @address: the next address inside that to be scanned
 136 * @rmap_list: link to the next rmap to be scanned in the rmap_list
 137 * @seqnr: count of completed full scans (needed when removing unstable node)
 138 *
 139 * There is only the one ksm_scan instance of this cursor structure.
 140 */
 141struct ksm_scan {
 142	struct ksm_mm_slot *mm_slot;
 143	unsigned long address;
 144	struct ksm_rmap_item **rmap_list;
 145	unsigned long seqnr;
 146};
 147
 148/**
 149 * struct ksm_stable_node - node of the stable rbtree
 150 * @node: rb node of this ksm page in the stable tree
 151 * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
 152 * @hlist_dup: linked into the stable_node->hlist with a stable_node chain
 153 * @list: linked into migrate_nodes, pending placement in the proper node tree
 154 * @hlist: hlist head of rmap_items using this ksm page
 155 * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
 156 * @chain_prune_time: time of the last full garbage collection
 157 * @rmap_hlist_len: number of rmap_item entries in hlist or STABLE_NODE_CHAIN
 158 * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
 159 */
 160struct ksm_stable_node {
 161	union {
 162		struct rb_node node;	/* when node of stable tree */
 163		struct {		/* when listed for migration */
 164			struct list_head *head;
 165			struct {
 166				struct hlist_node hlist_dup;
 167				struct list_head list;
 168			};
 169		};
 170	};
 171	struct hlist_head hlist;
 172	union {
 173		unsigned long kpfn;
 174		unsigned long chain_prune_time;
 175	};
 176	/*
 177	 * STABLE_NODE_CHAIN can be any negative number in
 178	 * rmap_hlist_len negative range, but better not -1 to be able
 179	 * to reliably detect underflows.
 180	 */
 181#define STABLE_NODE_CHAIN -1024
 182	int rmap_hlist_len;
 183#ifdef CONFIG_NUMA
 184	int nid;
 185#endif
 186};
 187
 188/**
 189 * struct ksm_rmap_item - reverse mapping item for virtual addresses
 190 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
 191 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
 192 * @nid: NUMA node id of unstable tree in which linked (may not match page)
 193 * @mm: the memory structure this rmap_item is pointing into
 194 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
 195 * @oldchecksum: previous checksum of the page at that virtual address
 196 * @node: rb node of this rmap_item in the unstable tree
 197 * @head: pointer to stable_node heading this list in the stable tree
 198 * @hlist: link into hlist of rmap_items hanging off that stable_node
 199 * @age: number of scan iterations since creation
 200 * @remaining_skips: how many scans to skip
 201 */
 202struct ksm_rmap_item {
 203	struct ksm_rmap_item *rmap_list;
 204	union {
 205		struct anon_vma *anon_vma;	/* when stable */
 206#ifdef CONFIG_NUMA
 207		int nid;		/* when node of unstable tree */
 208#endif
 209	};
 210	struct mm_struct *mm;
 211	unsigned long address;		/* + low bits used for flags below */
 212	unsigned int oldchecksum;	/* when unstable */
 213	rmap_age_t age;
 214	rmap_age_t remaining_skips;
 215	union {
 216		struct rb_node node;	/* when node of unstable tree */
 217		struct {		/* when listed from stable tree */
 218			struct ksm_stable_node *head;
 219			struct hlist_node hlist;
 220		};
 221	};
 222};
 223
 224#define SEQNR_MASK	0x0ff	/* low bits of unstable tree seqnr */
 225#define UNSTABLE_FLAG	0x100	/* is a node of the unstable tree */
 226#define STABLE_FLAG	0x200	/* is listed from the stable tree */
 227
 228/* The stable and unstable tree heads */
 229static struct rb_root one_stable_tree[1] = { RB_ROOT };
 230static struct rb_root one_unstable_tree[1] = { RB_ROOT };
 231static struct rb_root *root_stable_tree = one_stable_tree;
 232static struct rb_root *root_unstable_tree = one_unstable_tree;
 233
 234/* Recently migrated nodes of stable tree, pending proper placement */
 235static LIST_HEAD(migrate_nodes);
 236#define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev)
 237
 238#define MM_SLOTS_HASH_BITS 10
 239static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
 
 240
 241static struct ksm_mm_slot ksm_mm_head = {
 242	.slot.mm_node = LIST_HEAD_INIT(ksm_mm_head.slot.mm_node),
 243};
 244static struct ksm_scan ksm_scan = {
 245	.mm_slot = &ksm_mm_head,
 246};
 247
 248static struct kmem_cache *rmap_item_cache;
 249static struct kmem_cache *stable_node_cache;
 250static struct kmem_cache *mm_slot_cache;
 251
 252/* Default number of pages to scan per batch */
 253#define DEFAULT_PAGES_TO_SCAN 100
 254
 255/* The number of pages scanned */
 256static unsigned long ksm_pages_scanned;
 257
 258/* The number of nodes in the stable tree */
 259static unsigned long ksm_pages_shared;
 260
 261/* The number of page slots additionally sharing those nodes */
 262static unsigned long ksm_pages_sharing;
 263
 264/* The number of nodes in the unstable tree */
 265static unsigned long ksm_pages_unshared;
 266
 267/* The number of rmap_items in use: to calculate pages_volatile */
 268static unsigned long ksm_rmap_items;
 269
 270/* The number of stable_node chains */
 271static unsigned long ksm_stable_node_chains;
 272
 273/* The number of stable_node dups linked to the stable_node chains */
 274static unsigned long ksm_stable_node_dups;
 275
 276/* Delay in pruning stale stable_node_dups in the stable_node_chains */
 277static unsigned int ksm_stable_node_chains_prune_millisecs = 2000;
 278
 279/* Maximum number of page slots sharing a stable node */
 280static int ksm_max_page_sharing = 256;
 281
 282/* Number of pages ksmd should scan in one batch */
 283static unsigned int ksm_thread_pages_to_scan = DEFAULT_PAGES_TO_SCAN;
 284
 285/* Milliseconds ksmd should sleep between batches */
 286static unsigned int ksm_thread_sleep_millisecs = 20;
 287
 288/* Checksum of an empty (zeroed) page */
 289static unsigned int zero_checksum __read_mostly;
 290
 291/* Whether to merge empty (zeroed) pages with actual zero pages */
 292static bool ksm_use_zero_pages __read_mostly;
 293
 294/* Skip pages that couldn't be de-duplicated previously */
 295/* Default to true at least temporarily, for testing */
 296static bool ksm_smart_scan = true;
 297
 298/* The number of zero pages which is placed by KSM */
 299unsigned long ksm_zero_pages;
 300
 301/* The number of pages that have been skipped due to "smart scanning" */
 302static unsigned long ksm_pages_skipped;
 303
 304/* Don't scan more than max pages per batch. */
 305static unsigned long ksm_advisor_max_pages_to_scan = 30000;
 306
 307/* Min CPU for scanning pages per scan */
 308#define KSM_ADVISOR_MIN_CPU 10
 309
 310/* Max CPU for scanning pages per scan */
 311static unsigned int ksm_advisor_max_cpu =  70;
 312
 313/* Target scan time in seconds to analyze all KSM candidate pages. */
 314static unsigned long ksm_advisor_target_scan_time = 200;
 315
 316/* Exponentially weighted moving average. */
 317#define EWMA_WEIGHT 30
 318
 319/**
 320 * struct advisor_ctx - metadata for KSM advisor
 321 * @start_scan: start time of the current scan
 322 * @scan_time: scan time of previous scan
 323 * @change: change in percent to pages_to_scan parameter
 324 * @cpu_time: cpu time consumed by the ksmd thread in the previous scan
 325 */
 326struct advisor_ctx {
 327	ktime_t start_scan;
 328	unsigned long scan_time;
 329	unsigned long change;
 330	unsigned long long cpu_time;
 331};
 332static struct advisor_ctx advisor_ctx;
 333
 334/* Define different advisor's */
 335enum ksm_advisor_type {
 336	KSM_ADVISOR_NONE,
 337	KSM_ADVISOR_SCAN_TIME,
 338};
 339static enum ksm_advisor_type ksm_advisor;
 340
 341#ifdef CONFIG_SYSFS
 342/*
 343 * Only called through the sysfs control interface:
 344 */
 345
 346/* At least scan this many pages per batch. */
 347static unsigned long ksm_advisor_min_pages_to_scan = 500;
 348
 349static void set_advisor_defaults(void)
 350{
 351	if (ksm_advisor == KSM_ADVISOR_NONE) {
 352		ksm_thread_pages_to_scan = DEFAULT_PAGES_TO_SCAN;
 353	} else if (ksm_advisor == KSM_ADVISOR_SCAN_TIME) {
 354		advisor_ctx = (const struct advisor_ctx){ 0 };
 355		ksm_thread_pages_to_scan = ksm_advisor_min_pages_to_scan;
 356	}
 357}
 358#endif /* CONFIG_SYSFS */
 359
 360static inline void advisor_start_scan(void)
 361{
 362	if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
 363		advisor_ctx.start_scan = ktime_get();
 364}
 365
 366/*
 367 * Use previous scan time if available, otherwise use current scan time as an
 368 * approximation for the previous scan time.
 369 */
 370static inline unsigned long prev_scan_time(struct advisor_ctx *ctx,
 371					   unsigned long scan_time)
 372{
 373	return ctx->scan_time ? ctx->scan_time : scan_time;
 374}
 375
 376/* Calculate exponential weighted moving average */
 377static unsigned long ewma(unsigned long prev, unsigned long curr)
 378{
 379	return ((100 - EWMA_WEIGHT) * prev + EWMA_WEIGHT * curr) / 100;
 380}
 381
 382/*
 383 * The scan time advisor is based on the current scan rate and the target
 384 * scan rate.
 385 *
 386 *      new_pages_to_scan = pages_to_scan * (scan_time / target_scan_time)
 387 *
 388 * To avoid perturbations it calculates a change factor of previous changes.
 389 * A new change factor is calculated for each iteration and it uses an
 390 * exponentially weighted moving average. The new pages_to_scan value is
 391 * multiplied with that change factor:
 392 *
 393 *      new_pages_to_scan *= change facor
 394 *
 395 * The new_pages_to_scan value is limited by the cpu min and max values. It
 396 * calculates the cpu percent for the last scan and calculates the new
 397 * estimated cpu percent cost for the next scan. That value is capped by the
 398 * cpu min and max setting.
 399 *
 400 * In addition the new pages_to_scan value is capped by the max and min
 401 * limits.
 402 */
 403static void scan_time_advisor(void)
 404{
 405	unsigned int cpu_percent;
 406	unsigned long cpu_time;
 407	unsigned long cpu_time_diff;
 408	unsigned long cpu_time_diff_ms;
 409	unsigned long pages;
 410	unsigned long per_page_cost;
 411	unsigned long factor;
 412	unsigned long change;
 413	unsigned long last_scan_time;
 414	unsigned long scan_time;
 415
 416	/* Convert scan time to seconds */
 417	scan_time = div_s64(ktime_ms_delta(ktime_get(), advisor_ctx.start_scan),
 418			    MSEC_PER_SEC);
 419	scan_time = scan_time ? scan_time : 1;
 420
 421	/* Calculate CPU consumption of ksmd background thread */
 422	cpu_time = task_sched_runtime(current);
 423	cpu_time_diff = cpu_time - advisor_ctx.cpu_time;
 424	cpu_time_diff_ms = cpu_time_diff / 1000 / 1000;
 425
 426	cpu_percent = (cpu_time_diff_ms * 100) / (scan_time * 1000);
 427	cpu_percent = cpu_percent ? cpu_percent : 1;
 428	last_scan_time = prev_scan_time(&advisor_ctx, scan_time);
 429
 430	/* Calculate scan time as percentage of target scan time */
 431	factor = ksm_advisor_target_scan_time * 100 / scan_time;
 432	factor = factor ? factor : 1;
 433
 434	/*
 435	 * Calculate scan time as percentage of last scan time and use
 436	 * exponentially weighted average to smooth it
 437	 */
 438	change = scan_time * 100 / last_scan_time;
 439	change = change ? change : 1;
 440	change = ewma(advisor_ctx.change, change);
 441
 442	/* Calculate new scan rate based on target scan rate. */
 443	pages = ksm_thread_pages_to_scan * 100 / factor;
 444	/* Update pages_to_scan by weighted change percentage. */
 445	pages = pages * change / 100;
 446
 447	/* Cap new pages_to_scan value */
 448	per_page_cost = ksm_thread_pages_to_scan / cpu_percent;
 449	per_page_cost = per_page_cost ? per_page_cost : 1;
 450
 451	pages = min(pages, per_page_cost * ksm_advisor_max_cpu);
 452	pages = max(pages, per_page_cost * KSM_ADVISOR_MIN_CPU);
 453	pages = min(pages, ksm_advisor_max_pages_to_scan);
 454
 455	/* Update advisor context */
 456	advisor_ctx.change = change;
 457	advisor_ctx.scan_time = scan_time;
 458	advisor_ctx.cpu_time = cpu_time;
 459
 460	ksm_thread_pages_to_scan = pages;
 461	trace_ksm_advisor(scan_time, pages, cpu_percent);
 462}
 463
 464static void advisor_stop_scan(void)
 465{
 466	if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
 467		scan_time_advisor();
 468}
 469
 470#ifdef CONFIG_NUMA
 471/* Zeroed when merging across nodes is not allowed */
 472static unsigned int ksm_merge_across_nodes = 1;
 473static int ksm_nr_node_ids = 1;
 474#else
 475#define ksm_merge_across_nodes	1U
 476#define ksm_nr_node_ids		1
 477#endif
 478
 479#define KSM_RUN_STOP	0
 480#define KSM_RUN_MERGE	1
 481#define KSM_RUN_UNMERGE	2
 482#define KSM_RUN_OFFLINE	4
 483static unsigned long ksm_run = KSM_RUN_STOP;
 484static void wait_while_offlining(void);
 485
 486static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
 487static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait);
 488static DEFINE_MUTEX(ksm_thread_mutex);
 489static DEFINE_SPINLOCK(ksm_mmlist_lock);
 490
 491#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create(#__struct,\
 492		sizeof(struct __struct), __alignof__(struct __struct),\
 493		(__flags), NULL)
 494
 495static int __init ksm_slab_init(void)
 496{
 497	rmap_item_cache = KSM_KMEM_CACHE(ksm_rmap_item, 0);
 498	if (!rmap_item_cache)
 499		goto out;
 500
 501	stable_node_cache = KSM_KMEM_CACHE(ksm_stable_node, 0);
 502	if (!stable_node_cache)
 503		goto out_free1;
 504
 505	mm_slot_cache = KSM_KMEM_CACHE(ksm_mm_slot, 0);
 506	if (!mm_slot_cache)
 507		goto out_free2;
 508
 509	return 0;
 510
 511out_free2:
 512	kmem_cache_destroy(stable_node_cache);
 513out_free1:
 514	kmem_cache_destroy(rmap_item_cache);
 515out:
 516	return -ENOMEM;
 517}
 518
 519static void __init ksm_slab_free(void)
 520{
 521	kmem_cache_destroy(mm_slot_cache);
 522	kmem_cache_destroy(stable_node_cache);
 523	kmem_cache_destroy(rmap_item_cache);
 524	mm_slot_cache = NULL;
 525}
 526
 527static __always_inline bool is_stable_node_chain(struct ksm_stable_node *chain)
 528{
 529	return chain->rmap_hlist_len == STABLE_NODE_CHAIN;
 
 
 
 
 
 530}
 531
 532static __always_inline bool is_stable_node_dup(struct ksm_stable_node *dup)
 533{
 534	return dup->head == STABLE_NODE_DUP_HEAD;
 
 
 535}
 536
 537static inline void stable_node_chain_add_dup(struct ksm_stable_node *dup,
 538					     struct ksm_stable_node *chain)
 539{
 540	VM_BUG_ON(is_stable_node_dup(dup));
 541	dup->head = STABLE_NODE_DUP_HEAD;
 542	VM_BUG_ON(!is_stable_node_chain(chain));
 543	hlist_add_head(&dup->hlist_dup, &chain->hlist);
 544	ksm_stable_node_dups++;
 545}
 546
 547static inline void __stable_node_dup_del(struct ksm_stable_node *dup)
 548{
 549	VM_BUG_ON(!is_stable_node_dup(dup));
 550	hlist_del(&dup->hlist_dup);
 551	ksm_stable_node_dups--;
 552}
 553
 554static inline void stable_node_dup_del(struct ksm_stable_node *dup)
 555{
 556	VM_BUG_ON(is_stable_node_chain(dup));
 557	if (is_stable_node_dup(dup))
 558		__stable_node_dup_del(dup);
 559	else
 560		rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid));
 561#ifdef CONFIG_DEBUG_VM
 562	dup->head = NULL;
 563#endif
 564}
 565
 566static inline struct ksm_rmap_item *alloc_rmap_item(void)
 567{
 568	struct ksm_rmap_item *rmap_item;
 569
 570	rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL |
 571						__GFP_NORETRY | __GFP_NOWARN);
 572	if (rmap_item)
 573		ksm_rmap_items++;
 574	return rmap_item;
 575}
 576
 577static inline void free_rmap_item(struct ksm_rmap_item *rmap_item)
 578{
 579	ksm_rmap_items--;
 580	rmap_item->mm->ksm_rmap_items--;
 581	rmap_item->mm = NULL;	/* debug safety */
 582	kmem_cache_free(rmap_item_cache, rmap_item);
 
 
 
 
 
 
 583}
 584
 585static inline struct ksm_stable_node *alloc_stable_node(void)
 
 586{
 587	/*
 588	 * The allocation can take too long with GFP_KERNEL when memory is under
 589	 * pressure, which may lead to hung task warnings.  Adding __GFP_HIGH
 590	 * grants access to memory reserves, helping to avoid this problem.
 591	 */
 592	return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH);
 593}
 594
 595static inline void free_stable_node(struct ksm_stable_node *stable_node)
 596{
 597	VM_BUG_ON(stable_node->rmap_hlist_len &&
 598		  !is_stable_node_chain(stable_node));
 599	kmem_cache_free(stable_node_cache, stable_node);
 600}
 601
 602/*
 603 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
 604 * page tables after it has passed through ksm_exit() - which, if necessary,
 605 * takes mmap_lock briefly to serialize against them.  ksm_exit() does not set
 606 * a special flag: they can just back out as soon as mm_users goes to zero.
 607 * ksm_test_exit() is used throughout to make this test for exit: in some
 608 * places for correctness, in some places just to avoid unnecessary work.
 609 */
 610static inline bool ksm_test_exit(struct mm_struct *mm)
 611{
 612	return atomic_read(&mm->mm_users) == 0;
 613}
 614
 615static int break_ksm_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long next,
 616			struct mm_walk *walk)
 617{
 618	struct page *page = NULL;
 619	spinlock_t *ptl;
 620	pte_t *pte;
 621	pte_t ptent;
 622	int ret;
 623
 624	pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
 625	if (!pte)
 626		return 0;
 627	ptent = ptep_get(pte);
 628	if (pte_present(ptent)) {
 629		page = vm_normal_page(walk->vma, addr, ptent);
 630	} else if (!pte_none(ptent)) {
 631		swp_entry_t entry = pte_to_swp_entry(ptent);
 632
 633		/*
 634		 * As KSM pages remain KSM pages until freed, no need to wait
 635		 * here for migration to end.
 636		 */
 637		if (is_migration_entry(entry))
 638			page = pfn_swap_entry_to_page(entry);
 639	}
 640	/* return 1 if the page is an normal ksm page or KSM-placed zero page */
 641	ret = (page && PageKsm(page)) || is_ksm_zero_pte(ptent);
 642	pte_unmap_unlock(pte, ptl);
 643	return ret;
 644}
 645
 646static const struct mm_walk_ops break_ksm_ops = {
 647	.pmd_entry = break_ksm_pmd_entry,
 648	.walk_lock = PGWALK_RDLOCK,
 649};
 650
 651static const struct mm_walk_ops break_ksm_lock_vma_ops = {
 652	.pmd_entry = break_ksm_pmd_entry,
 653	.walk_lock = PGWALK_WRLOCK,
 654};
 655
 656/*
 657 * We use break_ksm to break COW on a ksm page by triggering unsharing,
 658 * such that the ksm page will get replaced by an exclusive anonymous page.
 659 *
 660 * We take great care only to touch a ksm page, in a VM_MERGEABLE vma,
 
 
 
 661 * in case the application has unmapped and remapped mm,addr meanwhile.
 662 * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
 663 * mmap of /dev/mem, where we would not want to touch it.
 664 *
 665 * FAULT_FLAG_REMOTE/FOLL_REMOTE are because we do this outside the context
 666 * of the process that owns 'vma'.  We also do not want to enforce
 667 * protection keys here anyway.
 668 */
 669static int break_ksm(struct vm_area_struct *vma, unsigned long addr, bool lock_vma)
 670{
 671	vm_fault_t ret = 0;
 672	const struct mm_walk_ops *ops = lock_vma ?
 673				&break_ksm_lock_vma_ops : &break_ksm_ops;
 674
 675	do {
 676		int ksm_page;
 677
 678		cond_resched();
 679		ksm_page = walk_page_range_vma(vma, addr, addr + 1, ops, NULL);
 680		if (WARN_ON_ONCE(ksm_page < 0))
 681			return ksm_page;
 682		if (!ksm_page)
 683			return 0;
 684		ret = handle_mm_fault(vma, addr,
 685				      FAULT_FLAG_UNSHARE | FAULT_FLAG_REMOTE,
 686				      NULL);
 687	} while (!(ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
 
 688	/*
 689	 * We must loop until we no longer find a KSM page because
 690	 * handle_mm_fault() may back out if there's any difficulty e.g. if
 691	 * pte accessed bit gets updated concurrently.
 
 
 
 692	 *
 693	 * VM_FAULT_SIGBUS could occur if we race with truncation of the
 694	 * backing file, which also invalidates anonymous pages: that's
 695	 * okay, that truncation will have unmapped the PageKsm for us.
 696	 *
 697	 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
 698	 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
 699	 * current task has TIF_MEMDIE set, and will be OOM killed on return
 700	 * to user; and ksmd, having no mm, would never be chosen for that.
 701	 *
 702	 * But if the mm is in a limited mem_cgroup, then the fault may fail
 703	 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
 704	 * even ksmd can fail in this way - though it's usually breaking ksm
 705	 * just to undo a merge it made a moment before, so unlikely to oom.
 706	 *
 707	 * That's a pity: we might therefore have more kernel pages allocated
 708	 * than we're counting as nodes in the stable tree; but ksm_do_scan
 709	 * will retry to break_cow on each pass, so should recover the page
 710	 * in due course.  The important thing is to not let VM_MERGEABLE
 711	 * be cleared while any such pages might remain in the area.
 712	 */
 713	return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
 714}
 715
 716static bool vma_ksm_compatible(struct vm_area_struct *vma)
 717{
 718	if (vma->vm_flags & (VM_SHARED  | VM_MAYSHARE   | VM_PFNMAP  |
 719			     VM_IO      | VM_DONTEXPAND | VM_HUGETLB |
 720			     VM_MIXEDMAP))
 721		return false;		/* just ignore the advice */
 722
 723	if (vma_is_dax(vma))
 724		return false;
 725
 726#ifdef VM_SAO
 727	if (vma->vm_flags & VM_SAO)
 728		return false;
 729#endif
 730#ifdef VM_SPARC_ADI
 731	if (vma->vm_flags & VM_SPARC_ADI)
 732		return false;
 733#endif
 734
 735	return true;
 736}
 737
 738static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
 739		unsigned long addr)
 740{
 741	struct vm_area_struct *vma;
 742	if (ksm_test_exit(mm))
 743		return NULL;
 744	vma = vma_lookup(mm, addr);
 745	if (!vma || !(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 746		return NULL;
 747	return vma;
 748}
 749
 750static void break_cow(struct ksm_rmap_item *rmap_item)
 751{
 752	struct mm_struct *mm = rmap_item->mm;
 753	unsigned long addr = rmap_item->address;
 754	struct vm_area_struct *vma;
 755
 756	/*
 757	 * It is not an accident that whenever we want to break COW
 758	 * to undo, we also need to drop a reference to the anon_vma.
 759	 */
 760	put_anon_vma(rmap_item->anon_vma);
 761
 762	mmap_read_lock(mm);
 763	vma = find_mergeable_vma(mm, addr);
 764	if (vma)
 765		break_ksm(vma, addr, false);
 766	mmap_read_unlock(mm);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 767}
 768
 769static struct page *get_mergeable_page(struct ksm_rmap_item *rmap_item)
 770{
 771	struct mm_struct *mm = rmap_item->mm;
 772	unsigned long addr = rmap_item->address;
 773	struct vm_area_struct *vma;
 774	struct page *page;
 775
 776	mmap_read_lock(mm);
 777	vma = find_mergeable_vma(mm, addr);
 778	if (!vma)
 
 
 
 
 779		goto out;
 780
 781	page = follow_page(vma, addr, FOLL_GET);
 782	if (IS_ERR_OR_NULL(page))
 783		goto out;
 784	if (is_zone_device_page(page))
 785		goto out_putpage;
 786	if (PageAnon(page)) {
 787		flush_anon_page(vma, page, addr);
 788		flush_dcache_page(page);
 789	} else {
 790out_putpage:
 791		put_page(page);
 792out:
 793		page = NULL;
 794	}
 795	mmap_read_unlock(mm);
 796	return page;
 797}
 798
 799/*
 800 * This helper is used for getting right index into array of tree roots.
 801 * When merge_across_nodes knob is set to 1, there are only two rb-trees for
 802 * stable and unstable pages from all nodes with roots in index 0. Otherwise,
 803 * every node has its own stable and unstable tree.
 804 */
 805static inline int get_kpfn_nid(unsigned long kpfn)
 806{
 807	return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
 808}
 809
 810static struct ksm_stable_node *alloc_stable_node_chain(struct ksm_stable_node *dup,
 811						   struct rb_root *root)
 812{
 813	struct ksm_stable_node *chain = alloc_stable_node();
 814	VM_BUG_ON(is_stable_node_chain(dup));
 815	if (likely(chain)) {
 816		INIT_HLIST_HEAD(&chain->hlist);
 817		chain->chain_prune_time = jiffies;
 818		chain->rmap_hlist_len = STABLE_NODE_CHAIN;
 819#if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA)
 820		chain->nid = NUMA_NO_NODE; /* debug */
 821#endif
 822		ksm_stable_node_chains++;
 823
 824		/*
 825		 * Put the stable node chain in the first dimension of
 826		 * the stable tree and at the same time remove the old
 827		 * stable node.
 828		 */
 829		rb_replace_node(&dup->node, &chain->node, root);
 830
 831		/*
 832		 * Move the old stable node to the second dimension
 833		 * queued in the hlist_dup. The invariant is that all
 834		 * dup stable_nodes in the chain->hlist point to pages
 835		 * that are write protected and have the exact same
 836		 * content.
 837		 */
 838		stable_node_chain_add_dup(dup, chain);
 839	}
 840	return chain;
 841}
 842
 843static inline void free_stable_node_chain(struct ksm_stable_node *chain,
 844					  struct rb_root *root)
 845{
 846	rb_erase(&chain->node, root);
 847	free_stable_node(chain);
 848	ksm_stable_node_chains--;
 849}
 850
 851static void remove_node_from_stable_tree(struct ksm_stable_node *stable_node)
 852{
 853	struct ksm_rmap_item *rmap_item;
 854
 855	/* check it's not STABLE_NODE_CHAIN or negative */
 856	BUG_ON(stable_node->rmap_hlist_len < 0);
 857
 858	hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
 859		if (rmap_item->hlist.next) {
 860			ksm_pages_sharing--;
 861			trace_ksm_remove_rmap_item(stable_node->kpfn, rmap_item, rmap_item->mm);
 862		} else {
 863			ksm_pages_shared--;
 864		}
 865
 866		rmap_item->mm->ksm_merging_pages--;
 867
 868		VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
 869		stable_node->rmap_hlist_len--;
 870		put_anon_vma(rmap_item->anon_vma);
 871		rmap_item->address &= PAGE_MASK;
 872		cond_resched();
 873	}
 874
 875	/*
 876	 * We need the second aligned pointer of the migrate_nodes
 877	 * list_head to stay clear from the rb_parent_color union
 878	 * (aligned and different than any node) and also different
 879	 * from &migrate_nodes. This will verify that future list.h changes
 880	 * don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it.
 881	 */
 882	BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes);
 883	BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1);
 884
 885	trace_ksm_remove_ksm_page(stable_node->kpfn);
 886	if (stable_node->head == &migrate_nodes)
 887		list_del(&stable_node->list);
 888	else
 889		stable_node_dup_del(stable_node);
 890	free_stable_node(stable_node);
 891}
 892
 893enum get_ksm_page_flags {
 894	GET_KSM_PAGE_NOLOCK,
 895	GET_KSM_PAGE_LOCK,
 896	GET_KSM_PAGE_TRYLOCK
 897};
 898
 899/*
 900 * get_ksm_page: checks if the page indicated by the stable node
 901 * is still its ksm page, despite having held no reference to it.
 902 * In which case we can trust the content of the page, and it
 903 * returns the gotten page; but if the page has now been zapped,
 904 * remove the stale node from the stable tree and return NULL.
 905 * But beware, the stable node's page might be being migrated.
 906 *
 907 * You would expect the stable_node to hold a reference to the ksm page.
 908 * But if it increments the page's count, swapping out has to wait for
 909 * ksmd to come around again before it can free the page, which may take
 910 * seconds or even minutes: much too unresponsive.  So instead we use a
 911 * "keyhole reference": access to the ksm page from the stable node peeps
 912 * out through its keyhole to see if that page still holds the right key,
 913 * pointing back to this stable node.  This relies on freeing a PageAnon
 914 * page to reset its page->mapping to NULL, and relies on no other use of
 915 * a page to put something that might look like our key in page->mapping.
 
 
 
 
 
 
 
 
 
 
 
 916 * is on its way to being freed; but it is an anomaly to bear in mind.
 917 */
 918static struct page *get_ksm_page(struct ksm_stable_node *stable_node,
 919				 enum get_ksm_page_flags flags)
 920{
 921	struct page *page;
 922	void *expected_mapping;
 923	unsigned long kpfn;
 924
 925	expected_mapping = (void *)((unsigned long)stable_node |
 926					PAGE_MAPPING_KSM);
 927again:
 928	kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */
 929	page = pfn_to_page(kpfn);
 930	if (READ_ONCE(page->mapping) != expected_mapping)
 
 931		goto stale;
 932
 933	/*
 934	 * We cannot do anything with the page while its refcount is 0.
 935	 * Usually 0 means free, or tail of a higher-order page: in which
 936	 * case this node is no longer referenced, and should be freed;
 937	 * however, it might mean that the page is under page_ref_freeze().
 938	 * The __remove_mapping() case is easy, again the node is now stale;
 939	 * the same is in reuse_ksm_page() case; but if page is swapcache
 940	 * in folio_migrate_mapping(), it might still be our page,
 941	 * in which case it's essential to keep the node.
 942	 */
 943	while (!get_page_unless_zero(page)) {
 944		/*
 945		 * Another check for page->mapping != expected_mapping would
 946		 * work here too.  We have chosen the !PageSwapCache test to
 947		 * optimize the common case, when the page is or is about to
 948		 * be freed: PageSwapCache is cleared (under spin_lock_irq)
 949		 * in the ref_freeze section of __remove_mapping(); but Anon
 950		 * page->mapping reset to NULL later, in free_pages_prepare().
 951		 */
 952		if (!PageSwapCache(page))
 953			goto stale;
 954		cpu_relax();
 955	}
 956
 957	if (READ_ONCE(page->mapping) != expected_mapping) {
 958		put_page(page);
 959		goto stale;
 960	}
 961
 962	if (flags == GET_KSM_PAGE_TRYLOCK) {
 963		if (!trylock_page(page)) {
 964			put_page(page);
 965			return ERR_PTR(-EBUSY);
 966		}
 967	} else if (flags == GET_KSM_PAGE_LOCK)
 968		lock_page(page);
 969
 970	if (flags != GET_KSM_PAGE_NOLOCK) {
 971		if (READ_ONCE(page->mapping) != expected_mapping) {
 972			unlock_page(page);
 973			put_page(page);
 974			goto stale;
 975		}
 976	}
 977	return page;
 978
 979stale:
 980	/*
 981	 * We come here from above when page->mapping or !PageSwapCache
 982	 * suggests that the node is stale; but it might be under migration.
 983	 * We need smp_rmb(), matching the smp_wmb() in folio_migrate_ksm(),
 984	 * before checking whether node->kpfn has been changed.
 985	 */
 986	smp_rmb();
 987	if (READ_ONCE(stable_node->kpfn) != kpfn)
 988		goto again;
 989	remove_node_from_stable_tree(stable_node);
 990	return NULL;
 991}
 992
 993/*
 994 * Removing rmap_item from stable or unstable tree.
 995 * This function will clean the information from the stable/unstable tree.
 996 */
 997static void remove_rmap_item_from_tree(struct ksm_rmap_item *rmap_item)
 998{
 999	if (rmap_item->address & STABLE_FLAG) {
1000		struct ksm_stable_node *stable_node;
1001		struct page *page;
1002
1003		stable_node = rmap_item->head;
1004		page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
1005		if (!page)
1006			goto out;
1007
 
1008		hlist_del(&rmap_item->hlist);
1009		unlock_page(page);
1010		put_page(page);
1011
1012		if (!hlist_empty(&stable_node->hlist))
1013			ksm_pages_sharing--;
1014		else
1015			ksm_pages_shared--;
1016
1017		rmap_item->mm->ksm_merging_pages--;
1018
1019		VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
1020		stable_node->rmap_hlist_len--;
1021
1022		put_anon_vma(rmap_item->anon_vma);
1023		rmap_item->head = NULL;
1024		rmap_item->address &= PAGE_MASK;
1025
1026	} else if (rmap_item->address & UNSTABLE_FLAG) {
1027		unsigned char age;
1028		/*
1029		 * Usually ksmd can and must skip the rb_erase, because
1030		 * root_unstable_tree was already reset to RB_ROOT.
1031		 * But be careful when an mm is exiting: do the rb_erase
1032		 * if this rmap_item was inserted by this scan, rather
1033		 * than left over from before.
1034		 */
1035		age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
1036		BUG_ON(age > 1);
1037		if (!age)
1038			rb_erase(&rmap_item->node,
1039				 root_unstable_tree + NUMA(rmap_item->nid));
1040		ksm_pages_unshared--;
1041		rmap_item->address &= PAGE_MASK;
1042	}
1043out:
1044	cond_resched();		/* we're called from many long loops */
1045}
1046
1047static void remove_trailing_rmap_items(struct ksm_rmap_item **rmap_list)
 
1048{
1049	while (*rmap_list) {
1050		struct ksm_rmap_item *rmap_item = *rmap_list;
1051		*rmap_list = rmap_item->rmap_list;
1052		remove_rmap_item_from_tree(rmap_item);
1053		free_rmap_item(rmap_item);
1054	}
1055}
1056
1057/*
1058 * Though it's very tempting to unmerge rmap_items from stable tree rather
1059 * than check every pte of a given vma, the locking doesn't quite work for
1060 * that - an rmap_item is assigned to the stable tree after inserting ksm
1061 * page and upping mmap_lock.  Nor does it fit with the way we skip dup'ing
1062 * rmap_items from parent to child at fork time (so as not to waste time
1063 * if exit comes before the next scan reaches it).
1064 *
1065 * Similarly, although we'd like to remove rmap_items (so updating counts
1066 * and freeing memory) when unmerging an area, it's easier to leave that
1067 * to the next pass of ksmd - consider, for example, how ksmd might be
1068 * in cmp_and_merge_page on one of the rmap_items we would be removing.
1069 */
1070static int unmerge_ksm_pages(struct vm_area_struct *vma,
1071			     unsigned long start, unsigned long end, bool lock_vma)
1072{
1073	unsigned long addr;
1074	int err = 0;
1075
1076	for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
1077		if (ksm_test_exit(vma->vm_mm))
1078			break;
1079		if (signal_pending(current))
1080			err = -ERESTARTSYS;
1081		else
1082			err = break_ksm(vma, addr, lock_vma);
1083	}
1084	return err;
1085}
1086
1087static inline struct ksm_stable_node *folio_stable_node(struct folio *folio)
1088{
1089	return folio_test_ksm(folio) ? folio_raw_mapping(folio) : NULL;
1090}
1091
1092static inline struct ksm_stable_node *page_stable_node(struct page *page)
1093{
1094	return folio_stable_node(page_folio(page));
1095}
1096
1097static inline void set_page_stable_node(struct page *page,
1098					struct ksm_stable_node *stable_node)
1099{
1100	VM_BUG_ON_PAGE(PageAnon(page) && PageAnonExclusive(page), page);
1101	page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM);
1102}
1103
1104#ifdef CONFIG_SYSFS
1105/*
1106 * Only called through the sysfs control interface:
1107 */
1108static int remove_stable_node(struct ksm_stable_node *stable_node)
1109{
1110	struct page *page;
1111	int err;
1112
1113	page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
1114	if (!page) {
1115		/*
1116		 * get_ksm_page did remove_node_from_stable_tree itself.
1117		 */
1118		return 0;
1119	}
1120
1121	/*
1122	 * Page could be still mapped if this races with __mmput() running in
1123	 * between ksm_exit() and exit_mmap(). Just refuse to let
1124	 * merge_across_nodes/max_page_sharing be switched.
1125	 */
1126	err = -EBUSY;
1127	if (!page_mapped(page)) {
1128		/*
1129		 * The stable node did not yet appear stale to get_ksm_page(),
1130		 * since that allows for an unmapped ksm page to be recognized
1131		 * right up until it is freed; but the node is safe to remove.
1132		 * This page might be in an LRU cache waiting to be freed,
1133		 * or it might be PageSwapCache (perhaps under writeback),
1134		 * or it might have been removed from swapcache a moment ago.
1135		 */
1136		set_page_stable_node(page, NULL);
1137		remove_node_from_stable_tree(stable_node);
1138		err = 0;
1139	}
1140
1141	unlock_page(page);
1142	put_page(page);
1143	return err;
1144}
1145
1146static int remove_stable_node_chain(struct ksm_stable_node *stable_node,
1147				    struct rb_root *root)
1148{
1149	struct ksm_stable_node *dup;
1150	struct hlist_node *hlist_safe;
1151
1152	if (!is_stable_node_chain(stable_node)) {
1153		VM_BUG_ON(is_stable_node_dup(stable_node));
1154		if (remove_stable_node(stable_node))
1155			return true;
1156		else
1157			return false;
1158	}
1159
1160	hlist_for_each_entry_safe(dup, hlist_safe,
1161				  &stable_node->hlist, hlist_dup) {
1162		VM_BUG_ON(!is_stable_node_dup(dup));
1163		if (remove_stable_node(dup))
1164			return true;
1165	}
1166	BUG_ON(!hlist_empty(&stable_node->hlist));
1167	free_stable_node_chain(stable_node, root);
1168	return false;
1169}
1170
1171static int remove_all_stable_nodes(void)
1172{
1173	struct ksm_stable_node *stable_node, *next;
1174	int nid;
1175	int err = 0;
1176
1177	for (nid = 0; nid < ksm_nr_node_ids; nid++) {
1178		while (root_stable_tree[nid].rb_node) {
1179			stable_node = rb_entry(root_stable_tree[nid].rb_node,
1180						struct ksm_stable_node, node);
1181			if (remove_stable_node_chain(stable_node,
1182						     root_stable_tree + nid)) {
1183				err = -EBUSY;
1184				break;	/* proceed to next nid */
1185			}
1186			cond_resched();
1187		}
1188	}
1189	list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
1190		if (remove_stable_node(stable_node))
1191			err = -EBUSY;
1192		cond_resched();
1193	}
1194	return err;
1195}
1196
1197static int unmerge_and_remove_all_rmap_items(void)
1198{
1199	struct ksm_mm_slot *mm_slot;
1200	struct mm_slot *slot;
1201	struct mm_struct *mm;
1202	struct vm_area_struct *vma;
1203	int err = 0;
1204
1205	spin_lock(&ksm_mmlist_lock);
1206	slot = list_entry(ksm_mm_head.slot.mm_node.next,
1207			  struct mm_slot, mm_node);
1208	ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
1209	spin_unlock(&ksm_mmlist_lock);
1210
1211	for (mm_slot = ksm_scan.mm_slot; mm_slot != &ksm_mm_head;
1212	     mm_slot = ksm_scan.mm_slot) {
1213		VMA_ITERATOR(vmi, mm_slot->slot.mm, 0);
1214
1215		mm = mm_slot->slot.mm;
1216		mmap_read_lock(mm);
1217
1218		/*
1219		 * Exit right away if mm is exiting to avoid lockdep issue in
1220		 * the maple tree
1221		 */
1222		if (ksm_test_exit(mm))
1223			goto mm_exiting;
1224
1225		for_each_vma(vmi, vma) {
1226			if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
1227				continue;
1228			err = unmerge_ksm_pages(vma,
1229						vma->vm_start, vma->vm_end, false);
1230			if (err)
1231				goto error;
1232		}
1233
1234mm_exiting:
1235		remove_trailing_rmap_items(&mm_slot->rmap_list);
1236		mmap_read_unlock(mm);
1237
1238		spin_lock(&ksm_mmlist_lock);
1239		slot = list_entry(mm_slot->slot.mm_node.next,
1240				  struct mm_slot, mm_node);
1241		ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
1242		if (ksm_test_exit(mm)) {
1243			hash_del(&mm_slot->slot.hash);
1244			list_del(&mm_slot->slot.mm_node);
1245			spin_unlock(&ksm_mmlist_lock);
1246
1247			mm_slot_free(mm_slot_cache, mm_slot);
1248			clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1249			clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
1250			mmdrop(mm);
1251		} else
1252			spin_unlock(&ksm_mmlist_lock);
 
 
1253	}
1254
1255	/* Clean up stable nodes, but don't worry if some are still busy */
1256	remove_all_stable_nodes();
1257	ksm_scan.seqnr = 0;
1258	return 0;
1259
1260error:
1261	mmap_read_unlock(mm);
1262	spin_lock(&ksm_mmlist_lock);
1263	ksm_scan.mm_slot = &ksm_mm_head;
1264	spin_unlock(&ksm_mmlist_lock);
1265	return err;
1266}
1267#endif /* CONFIG_SYSFS */
1268
1269static u32 calc_checksum(struct page *page)
1270{
1271	u32 checksum;
1272	void *addr = kmap_local_page(page);
1273	checksum = xxhash(addr, PAGE_SIZE, 0);
1274	kunmap_local(addr);
1275	return checksum;
1276}
1277
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1278static int write_protect_page(struct vm_area_struct *vma, struct page *page,
1279			      pte_t *orig_pte)
1280{
1281	struct mm_struct *mm = vma->vm_mm;
1282	DEFINE_PAGE_VMA_WALK(pvmw, page, vma, 0, 0);
 
 
1283	int swapped;
1284	int err = -EFAULT;
1285	struct mmu_notifier_range range;
1286	bool anon_exclusive;
1287	pte_t entry;
1288
1289	pvmw.address = page_address_in_vma(page, vma);
1290	if (pvmw.address == -EFAULT)
1291		goto out;
1292
1293	BUG_ON(PageTransCompound(page));
 
 
 
 
 
 
1294
1295	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, pvmw.address,
1296				pvmw.address + PAGE_SIZE);
1297	mmu_notifier_invalidate_range_start(&range);
1298
1299	if (!page_vma_mapped_walk(&pvmw))
1300		goto out_mn;
1301	if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?"))
1302		goto out_unlock;
1303
1304	anon_exclusive = PageAnonExclusive(page);
1305	entry = ptep_get(pvmw.pte);
1306	if (pte_write(entry) || pte_dirty(entry) ||
1307	    anon_exclusive || mm_tlb_flush_pending(mm)) {
1308		swapped = PageSwapCache(page);
1309		flush_cache_page(vma, pvmw.address, page_to_pfn(page));
1310		/*
1311		 * Ok this is tricky, when get_user_pages_fast() run it doesn't
1312		 * take any lock, therefore the check that we are going to make
1313		 * with the pagecount against the mapcount is racy and
1314		 * O_DIRECT can happen right after the check.
1315		 * So we clear the pte and flush the tlb before the check
1316		 * this assure us that no O_DIRECT can happen after the check
1317		 * or in the middle of the check.
1318		 *
1319		 * No need to notify as we are downgrading page table to read
1320		 * only not changing it to point to a new page.
1321		 *
1322		 * See Documentation/mm/mmu_notifier.rst
1323		 */
1324		entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte);
1325		/*
1326		 * Check that no O_DIRECT or similar I/O is in progress on the
1327		 * page
1328		 */
1329		if (page_mapcount(page) + 1 + swapped != page_count(page)) {
1330			set_pte_at(mm, pvmw.address, pvmw.pte, entry);
1331			goto out_unlock;
1332		}
1333
1334		/* See folio_try_share_anon_rmap_pte(): clear PTE first. */
1335		if (anon_exclusive &&
1336		    folio_try_share_anon_rmap_pte(page_folio(page), page)) {
1337			set_pte_at(mm, pvmw.address, pvmw.pte, entry);
1338			goto out_unlock;
1339		}
1340
1341		if (pte_dirty(entry))
1342			set_page_dirty(page);
1343		entry = pte_mkclean(entry);
1344
1345		if (pte_write(entry))
1346			entry = pte_wrprotect(entry);
1347
1348		set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry);
1349	}
1350	*orig_pte = entry;
1351	err = 0;
1352
1353out_unlock:
1354	page_vma_mapped_walk_done(&pvmw);
1355out_mn:
1356	mmu_notifier_invalidate_range_end(&range);
1357out:
1358	return err;
1359}
1360
1361/**
1362 * replace_page - replace page in vma by new ksm page
1363 * @vma:      vma that holds the pte pointing to page
1364 * @page:     the page we are replacing by kpage
1365 * @kpage:    the ksm page we replace page by
1366 * @orig_pte: the original value of the pte
1367 *
1368 * Returns 0 on success, -EFAULT on failure.
1369 */
1370static int replace_page(struct vm_area_struct *vma, struct page *page,
1371			struct page *kpage, pte_t orig_pte)
1372{
1373	struct folio *kfolio = page_folio(kpage);
1374	struct mm_struct *mm = vma->vm_mm;
1375	struct folio *folio;
 
1376	pmd_t *pmd;
1377	pmd_t pmde;
1378	pte_t *ptep;
1379	pte_t newpte;
1380	spinlock_t *ptl;
1381	unsigned long addr;
1382	int err = -EFAULT;
1383	struct mmu_notifier_range range;
1384
1385	addr = page_address_in_vma(page, vma);
1386	if (addr == -EFAULT)
1387		goto out;
1388
1389	pmd = mm_find_pmd(mm, addr);
1390	if (!pmd)
1391		goto out;
1392	/*
1393	 * Some THP functions use the sequence pmdp_huge_clear_flush(), set_pmd_at()
1394	 * without holding anon_vma lock for write.  So when looking for a
1395	 * genuine pmde (in which to find pte), test present and !THP together.
1396	 */
1397	pmde = pmdp_get_lockless(pmd);
1398	if (!pmd_present(pmde) || pmd_trans_huge(pmde))
1399		goto out;
1400
1401	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, addr,
1402				addr + PAGE_SIZE);
1403	mmu_notifier_invalidate_range_start(&range);
 
1404
1405	ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
1406	if (!ptep)
1407		goto out_mn;
1408	if (!pte_same(ptep_get(ptep), orig_pte)) {
1409		pte_unmap_unlock(ptep, ptl);
1410		goto out_mn;
1411	}
1412	VM_BUG_ON_PAGE(PageAnonExclusive(page), page);
1413	VM_BUG_ON_FOLIO(folio_test_anon(kfolio) && PageAnonExclusive(kpage),
1414			kfolio);
1415
1416	/*
1417	 * No need to check ksm_use_zero_pages here: we can only have a
1418	 * zero_page here if ksm_use_zero_pages was enabled already.
1419	 */
1420	if (!is_zero_pfn(page_to_pfn(kpage))) {
1421		folio_get(kfolio);
1422		folio_add_anon_rmap_pte(kfolio, kpage, vma, addr, RMAP_NONE);
1423		newpte = mk_pte(kpage, vma->vm_page_prot);
1424	} else {
1425		/*
1426		 * Use pte_mkdirty to mark the zero page mapped by KSM, and then
1427		 * we can easily track all KSM-placed zero pages by checking if
1428		 * the dirty bit in zero page's PTE is set.
1429		 */
1430		newpte = pte_mkdirty(pte_mkspecial(pfn_pte(page_to_pfn(kpage), vma->vm_page_prot)));
1431		ksm_zero_pages++;
1432		mm->ksm_zero_pages++;
1433		/*
1434		 * We're replacing an anonymous page with a zero page, which is
1435		 * not anonymous. We need to do proper accounting otherwise we
1436		 * will get wrong values in /proc, and a BUG message in dmesg
1437		 * when tearing down the mm.
1438		 */
1439		dec_mm_counter(mm, MM_ANONPAGES);
1440	}
1441
1442	flush_cache_page(vma, addr, pte_pfn(ptep_get(ptep)));
1443	/*
1444	 * No need to notify as we are replacing a read only page with another
1445	 * read only page with the same content.
1446	 *
1447	 * See Documentation/mm/mmu_notifier.rst
1448	 */
1449	ptep_clear_flush(vma, addr, ptep);
1450	set_pte_at_notify(mm, addr, ptep, newpte);
1451
1452	folio = page_folio(page);
1453	folio_remove_rmap_pte(folio, page, vma);
1454	if (!folio_mapped(folio))
1455		folio_free_swap(folio);
1456	folio_put(folio);
1457
1458	pte_unmap_unlock(ptep, ptl);
1459	err = 0;
1460out_mn:
1461	mmu_notifier_invalidate_range_end(&range);
1462out:
1463	return err;
1464}
1465
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1466/*
1467 * try_to_merge_one_page - take two pages and merge them into one
1468 * @vma: the vma that holds the pte pointing to page
1469 * @page: the PageAnon page that we want to replace with kpage
1470 * @kpage: the PageKsm page that we want to map instead of page,
1471 *         or NULL the first time when we want to use page as kpage.
1472 *
1473 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1474 */
1475static int try_to_merge_one_page(struct vm_area_struct *vma,
1476				 struct page *page, struct page *kpage)
1477{
1478	pte_t orig_pte = __pte(0);
1479	int err = -EFAULT;
1480
1481	if (page == kpage)			/* ksm page forked */
1482		return 0;
1483
 
 
 
 
 
1484	if (!PageAnon(page))
1485		goto out;
1486
1487	/*
1488	 * We need the page lock to read a stable PageSwapCache in
1489	 * write_protect_page().  We use trylock_page() instead of
1490	 * lock_page() because we don't want to wait here - we
1491	 * prefer to continue scanning and merging different pages,
1492	 * then come back to this page when it is unlocked.
1493	 */
1494	if (!trylock_page(page))
1495		goto out;
1496
1497	if (PageTransCompound(page)) {
1498		if (split_huge_page(page))
1499			goto out_unlock;
1500	}
1501
1502	/*
1503	 * If this anonymous page is mapped only here, its pte may need
1504	 * to be write-protected.  If it's mapped elsewhere, all of its
1505	 * ptes are necessarily already write-protected.  But in either
1506	 * case, we need to lock and check page_count is not raised.
1507	 */
1508	if (write_protect_page(vma, page, &orig_pte) == 0) {
1509		if (!kpage) {
1510			/*
1511			 * While we hold page lock, upgrade page from
1512			 * PageAnon+anon_vma to PageKsm+NULL stable_node:
1513			 * stable_tree_insert() will update stable_node.
1514			 */
1515			set_page_stable_node(page, NULL);
1516			mark_page_accessed(page);
1517			/*
1518			 * Page reclaim just frees a clean page with no dirty
1519			 * ptes: make sure that the ksm page would be swapped.
1520			 */
1521			if (!PageDirty(page))
1522				SetPageDirty(page);
1523			err = 0;
1524		} else if (pages_identical(page, kpage))
1525			err = replace_page(vma, page, kpage, orig_pte);
1526	}
1527
1528out_unlock:
 
 
 
 
 
 
 
 
 
1529	unlock_page(page);
1530out:
1531	return err;
1532}
1533
1534/*
1535 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1536 * but no new kernel page is allocated: kpage must already be a ksm page.
1537 *
1538 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1539 */
1540static int try_to_merge_with_ksm_page(struct ksm_rmap_item *rmap_item,
1541				      struct page *page, struct page *kpage)
1542{
1543	struct mm_struct *mm = rmap_item->mm;
1544	struct vm_area_struct *vma;
1545	int err = -EFAULT;
1546
1547	mmap_read_lock(mm);
1548	vma = find_mergeable_vma(mm, rmap_item->address);
1549	if (!vma)
 
 
1550		goto out;
1551
1552	err = try_to_merge_one_page(vma, page, kpage);
1553	if (err)
1554		goto out;
1555
1556	/* Unstable nid is in union with stable anon_vma: remove first */
1557	remove_rmap_item_from_tree(rmap_item);
1558
1559	/* Must get reference to anon_vma while still holding mmap_lock */
1560	rmap_item->anon_vma = vma->anon_vma;
1561	get_anon_vma(vma->anon_vma);
1562out:
1563	mmap_read_unlock(mm);
1564	trace_ksm_merge_with_ksm_page(kpage, page_to_pfn(kpage ? kpage : page),
1565				rmap_item, mm, err);
1566	return err;
1567}
1568
1569/*
1570 * try_to_merge_two_pages - take two identical pages and prepare them
1571 * to be merged into one page.
1572 *
1573 * This function returns the kpage if we successfully merged two identical
1574 * pages into one ksm page, NULL otherwise.
1575 *
1576 * Note that this function upgrades page to ksm page: if one of the pages
1577 * is already a ksm page, try_to_merge_with_ksm_page should be used.
1578 */
1579static struct page *try_to_merge_two_pages(struct ksm_rmap_item *rmap_item,
1580					   struct page *page,
1581					   struct ksm_rmap_item *tree_rmap_item,
1582					   struct page *tree_page)
1583{
1584	int err;
1585
1586	err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
1587	if (!err) {
1588		err = try_to_merge_with_ksm_page(tree_rmap_item,
1589							tree_page, page);
1590		/*
1591		 * If that fails, we have a ksm page with only one pte
1592		 * pointing to it: so break it.
1593		 */
1594		if (err)
1595			break_cow(rmap_item);
1596	}
1597	return err ? NULL : page;
1598}
1599
1600static __always_inline
1601bool __is_page_sharing_candidate(struct ksm_stable_node *stable_node, int offset)
1602{
1603	VM_BUG_ON(stable_node->rmap_hlist_len < 0);
1604	/*
1605	 * Check that at least one mapping still exists, otherwise
1606	 * there's no much point to merge and share with this
1607	 * stable_node, as the underlying tree_page of the other
1608	 * sharer is going to be freed soon.
1609	 */
1610	return stable_node->rmap_hlist_len &&
1611		stable_node->rmap_hlist_len + offset < ksm_max_page_sharing;
1612}
1613
1614static __always_inline
1615bool is_page_sharing_candidate(struct ksm_stable_node *stable_node)
1616{
1617	return __is_page_sharing_candidate(stable_node, 0);
1618}
1619
1620static struct page *stable_node_dup(struct ksm_stable_node **_stable_node_dup,
1621				    struct ksm_stable_node **_stable_node,
1622				    struct rb_root *root,
1623				    bool prune_stale_stable_nodes)
1624{
1625	struct ksm_stable_node *dup, *found = NULL, *stable_node = *_stable_node;
1626	struct hlist_node *hlist_safe;
1627	struct page *_tree_page, *tree_page = NULL;
1628	int nr = 0;
1629	int found_rmap_hlist_len;
1630
1631	if (!prune_stale_stable_nodes ||
1632	    time_before(jiffies, stable_node->chain_prune_time +
1633			msecs_to_jiffies(
1634				ksm_stable_node_chains_prune_millisecs)))
1635		prune_stale_stable_nodes = false;
1636	else
1637		stable_node->chain_prune_time = jiffies;
1638
1639	hlist_for_each_entry_safe(dup, hlist_safe,
1640				  &stable_node->hlist, hlist_dup) {
1641		cond_resched();
1642		/*
1643		 * We must walk all stable_node_dup to prune the stale
1644		 * stable nodes during lookup.
1645		 *
1646		 * get_ksm_page can drop the nodes from the
1647		 * stable_node->hlist if they point to freed pages
1648		 * (that's why we do a _safe walk). The "dup"
1649		 * stable_node parameter itself will be freed from
1650		 * under us if it returns NULL.
1651		 */
1652		_tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK);
1653		if (!_tree_page)
1654			continue;
1655		nr += 1;
1656		if (is_page_sharing_candidate(dup)) {
1657			if (!found ||
1658			    dup->rmap_hlist_len > found_rmap_hlist_len) {
1659				if (found)
1660					put_page(tree_page);
1661				found = dup;
1662				found_rmap_hlist_len = found->rmap_hlist_len;
1663				tree_page = _tree_page;
1664
1665				/* skip put_page for found dup */
1666				if (!prune_stale_stable_nodes)
1667					break;
1668				continue;
1669			}
1670		}
1671		put_page(_tree_page);
1672	}
1673
1674	if (found) {
1675		/*
1676		 * nr is counting all dups in the chain only if
1677		 * prune_stale_stable_nodes is true, otherwise we may
1678		 * break the loop at nr == 1 even if there are
1679		 * multiple entries.
1680		 */
1681		if (prune_stale_stable_nodes && nr == 1) {
1682			/*
1683			 * If there's not just one entry it would
1684			 * corrupt memory, better BUG_ON. In KSM
1685			 * context with no lock held it's not even
1686			 * fatal.
1687			 */
1688			BUG_ON(stable_node->hlist.first->next);
1689
1690			/*
1691			 * There's just one entry and it is below the
1692			 * deduplication limit so drop the chain.
1693			 */
1694			rb_replace_node(&stable_node->node, &found->node,
1695					root);
1696			free_stable_node(stable_node);
1697			ksm_stable_node_chains--;
1698			ksm_stable_node_dups--;
1699			/*
1700			 * NOTE: the caller depends on the stable_node
1701			 * to be equal to stable_node_dup if the chain
1702			 * was collapsed.
1703			 */
1704			*_stable_node = found;
1705			/*
1706			 * Just for robustness, as stable_node is
1707			 * otherwise left as a stable pointer, the
1708			 * compiler shall optimize it away at build
1709			 * time.
1710			 */
1711			stable_node = NULL;
1712		} else if (stable_node->hlist.first != &found->hlist_dup &&
1713			   __is_page_sharing_candidate(found, 1)) {
1714			/*
1715			 * If the found stable_node dup can accept one
1716			 * more future merge (in addition to the one
1717			 * that is underway) and is not at the head of
1718			 * the chain, put it there so next search will
1719			 * be quicker in the !prune_stale_stable_nodes
1720			 * case.
1721			 *
1722			 * NOTE: it would be inaccurate to use nr > 1
1723			 * instead of checking the hlist.first pointer
1724			 * directly, because in the
1725			 * prune_stale_stable_nodes case "nr" isn't
1726			 * the position of the found dup in the chain,
1727			 * but the total number of dups in the chain.
1728			 */
1729			hlist_del(&found->hlist_dup);
1730			hlist_add_head(&found->hlist_dup,
1731				       &stable_node->hlist);
1732		}
1733	}
1734
1735	*_stable_node_dup = found;
1736	return tree_page;
1737}
1738
1739static struct ksm_stable_node *stable_node_dup_any(struct ksm_stable_node *stable_node,
1740					       struct rb_root *root)
1741{
1742	if (!is_stable_node_chain(stable_node))
1743		return stable_node;
1744	if (hlist_empty(&stable_node->hlist)) {
1745		free_stable_node_chain(stable_node, root);
1746		return NULL;
1747	}
1748	return hlist_entry(stable_node->hlist.first,
1749			   typeof(*stable_node), hlist_dup);
1750}
1751
1752/*
1753 * Like for get_ksm_page, this function can free the *_stable_node and
1754 * *_stable_node_dup if the returned tree_page is NULL.
1755 *
1756 * It can also free and overwrite *_stable_node with the found
1757 * stable_node_dup if the chain is collapsed (in which case
1758 * *_stable_node will be equal to *_stable_node_dup like if the chain
1759 * never existed). It's up to the caller to verify tree_page is not
1760 * NULL before dereferencing *_stable_node or *_stable_node_dup.
1761 *
1762 * *_stable_node_dup is really a second output parameter of this
1763 * function and will be overwritten in all cases, the caller doesn't
1764 * need to initialize it.
1765 */
1766static struct page *__stable_node_chain(struct ksm_stable_node **_stable_node_dup,
1767					struct ksm_stable_node **_stable_node,
1768					struct rb_root *root,
1769					bool prune_stale_stable_nodes)
1770{
1771	struct ksm_stable_node *stable_node = *_stable_node;
1772	if (!is_stable_node_chain(stable_node)) {
1773		if (is_page_sharing_candidate(stable_node)) {
1774			*_stable_node_dup = stable_node;
1775			return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK);
1776		}
1777		/*
1778		 * _stable_node_dup set to NULL means the stable_node
1779		 * reached the ksm_max_page_sharing limit.
1780		 */
1781		*_stable_node_dup = NULL;
1782		return NULL;
1783	}
1784	return stable_node_dup(_stable_node_dup, _stable_node, root,
1785			       prune_stale_stable_nodes);
1786}
1787
1788static __always_inline struct page *chain_prune(struct ksm_stable_node **s_n_d,
1789						struct ksm_stable_node **s_n,
1790						struct rb_root *root)
1791{
1792	return __stable_node_chain(s_n_d, s_n, root, true);
1793}
1794
1795static __always_inline struct page *chain(struct ksm_stable_node **s_n_d,
1796					  struct ksm_stable_node *s_n,
1797					  struct rb_root *root)
1798{
1799	struct ksm_stable_node *old_stable_node = s_n;
1800	struct page *tree_page;
1801
1802	tree_page = __stable_node_chain(s_n_d, &s_n, root, false);
1803	/* not pruning dups so s_n cannot have changed */
1804	VM_BUG_ON(s_n != old_stable_node);
1805	return tree_page;
1806}
1807
1808/*
1809 * stable_tree_search - search for page inside the stable tree
1810 *
1811 * This function checks if there is a page inside the stable tree
1812 * with identical content to the page that we are scanning right now.
1813 *
1814 * This function returns the stable tree node of identical content if found,
1815 * NULL otherwise.
1816 */
1817static struct page *stable_tree_search(struct page *page)
1818{
1819	int nid;
1820	struct rb_root *root;
1821	struct rb_node **new;
1822	struct rb_node *parent;
1823	struct ksm_stable_node *stable_node, *stable_node_dup, *stable_node_any;
1824	struct ksm_stable_node *page_node;
1825
1826	page_node = page_stable_node(page);
1827	if (page_node && page_node->head != &migrate_nodes) {
1828		/* ksm page forked */
1829		get_page(page);
1830		return page;
1831	}
1832
1833	nid = get_kpfn_nid(page_to_pfn(page));
1834	root = root_stable_tree + nid;
1835again:
1836	new = &root->rb_node;
1837	parent = NULL;
1838
1839	while (*new) {
1840		struct page *tree_page;
1841		int ret;
1842
1843		cond_resched();
1844		stable_node = rb_entry(*new, struct ksm_stable_node, node);
1845		stable_node_any = NULL;
1846		tree_page = chain_prune(&stable_node_dup, &stable_node,	root);
1847		/*
1848		 * NOTE: stable_node may have been freed by
1849		 * chain_prune() if the returned stable_node_dup is
1850		 * not NULL. stable_node_dup may have been inserted in
1851		 * the rbtree instead as a regular stable_node (in
1852		 * order to collapse the stable_node chain if a single
1853		 * stable_node dup was found in it). In such case the
1854		 * stable_node is overwritten by the callee to point
1855		 * to the stable_node_dup that was collapsed in the
1856		 * stable rbtree and stable_node will be equal to
1857		 * stable_node_dup like if the chain never existed.
1858		 */
1859		if (!stable_node_dup) {
1860			/*
1861			 * Either all stable_node dups were full in
1862			 * this stable_node chain, or this chain was
1863			 * empty and should be rb_erased.
1864			 */
1865			stable_node_any = stable_node_dup_any(stable_node,
1866							      root);
1867			if (!stable_node_any) {
1868				/* rb_erase just run */
1869				goto again;
1870			}
1871			/*
1872			 * Take any of the stable_node dups page of
1873			 * this stable_node chain to let the tree walk
1874			 * continue. All KSM pages belonging to the
1875			 * stable_node dups in a stable_node chain
1876			 * have the same content and they're
1877			 * write protected at all times. Any will work
1878			 * fine to continue the walk.
1879			 */
1880			tree_page = get_ksm_page(stable_node_any,
1881						 GET_KSM_PAGE_NOLOCK);
1882		}
1883		VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1884		if (!tree_page) {
1885			/*
1886			 * If we walked over a stale stable_node,
1887			 * get_ksm_page() will call rb_erase() and it
1888			 * may rebalance the tree from under us. So
1889			 * restart the search from scratch. Returning
1890			 * NULL would be safe too, but we'd generate
1891			 * false negative insertions just because some
1892			 * stable_node was stale.
1893			 */
1894			goto again;
1895		}
1896
1897		ret = memcmp_pages(page, tree_page);
1898		put_page(tree_page);
1899
1900		parent = *new;
1901		if (ret < 0)
1902			new = &parent->rb_left;
1903		else if (ret > 0)
1904			new = &parent->rb_right;
1905		else {
1906			if (page_node) {
1907				VM_BUG_ON(page_node->head != &migrate_nodes);
1908				/*
1909				 * Test if the migrated page should be merged
1910				 * into a stable node dup. If the mapcount is
1911				 * 1 we can migrate it with another KSM page
1912				 * without adding it to the chain.
1913				 */
1914				if (page_mapcount(page) > 1)
1915					goto chain_append;
1916			}
1917
1918			if (!stable_node_dup) {
1919				/*
1920				 * If the stable_node is a chain and
1921				 * we got a payload match in memcmp
1922				 * but we cannot merge the scanned
1923				 * page in any of the existing
1924				 * stable_node dups because they're
1925				 * all full, we need to wait the
1926				 * scanned page to find itself a match
1927				 * in the unstable tree to create a
1928				 * brand new KSM page to add later to
1929				 * the dups of this stable_node.
1930				 */
1931				return NULL;
1932			}
1933
1934			/*
1935			 * Lock and unlock the stable_node's page (which
1936			 * might already have been migrated) so that page
1937			 * migration is sure to notice its raised count.
1938			 * It would be more elegant to return stable_node
1939			 * than kpage, but that involves more changes.
1940			 */
1941			tree_page = get_ksm_page(stable_node_dup,
1942						 GET_KSM_PAGE_TRYLOCK);
1943
1944			if (PTR_ERR(tree_page) == -EBUSY)
1945				return ERR_PTR(-EBUSY);
1946
1947			if (unlikely(!tree_page))
1948				/*
1949				 * The tree may have been rebalanced,
1950				 * so re-evaluate parent and new.
1951				 */
1952				goto again;
1953			unlock_page(tree_page);
1954
1955			if (get_kpfn_nid(stable_node_dup->kpfn) !=
1956			    NUMA(stable_node_dup->nid)) {
1957				put_page(tree_page);
1958				goto replace;
1959			}
1960			return tree_page;
1961		}
1962	}
1963
1964	if (!page_node)
1965		return NULL;
1966
1967	list_del(&page_node->list);
1968	DO_NUMA(page_node->nid = nid);
1969	rb_link_node(&page_node->node, parent, new);
1970	rb_insert_color(&page_node->node, root);
1971out:
1972	if (is_page_sharing_candidate(page_node)) {
1973		get_page(page);
1974		return page;
1975	} else
1976		return NULL;
1977
1978replace:
1979	/*
1980	 * If stable_node was a chain and chain_prune collapsed it,
1981	 * stable_node has been updated to be the new regular
1982	 * stable_node. A collapse of the chain is indistinguishable
1983	 * from the case there was no chain in the stable
1984	 * rbtree. Otherwise stable_node is the chain and
1985	 * stable_node_dup is the dup to replace.
1986	 */
1987	if (stable_node_dup == stable_node) {
1988		VM_BUG_ON(is_stable_node_chain(stable_node_dup));
1989		VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1990		/* there is no chain */
1991		if (page_node) {
1992			VM_BUG_ON(page_node->head != &migrate_nodes);
1993			list_del(&page_node->list);
1994			DO_NUMA(page_node->nid = nid);
1995			rb_replace_node(&stable_node_dup->node,
1996					&page_node->node,
1997					root);
1998			if (is_page_sharing_candidate(page_node))
1999				get_page(page);
2000			else
2001				page = NULL;
2002		} else {
2003			rb_erase(&stable_node_dup->node, root);
2004			page = NULL;
2005		}
2006	} else {
2007		VM_BUG_ON(!is_stable_node_chain(stable_node));
2008		__stable_node_dup_del(stable_node_dup);
2009		if (page_node) {
2010			VM_BUG_ON(page_node->head != &migrate_nodes);
2011			list_del(&page_node->list);
2012			DO_NUMA(page_node->nid = nid);
2013			stable_node_chain_add_dup(page_node, stable_node);
2014			if (is_page_sharing_candidate(page_node))
2015				get_page(page);
2016			else
2017				page = NULL;
2018		} else {
2019			page = NULL;
2020		}
2021	}
2022	stable_node_dup->head = &migrate_nodes;
2023	list_add(&stable_node_dup->list, stable_node_dup->head);
2024	return page;
2025
2026chain_append:
2027	/* stable_node_dup could be null if it reached the limit */
2028	if (!stable_node_dup)
2029		stable_node_dup = stable_node_any;
2030	/*
2031	 * If stable_node was a chain and chain_prune collapsed it,
2032	 * stable_node has been updated to be the new regular
2033	 * stable_node. A collapse of the chain is indistinguishable
2034	 * from the case there was no chain in the stable
2035	 * rbtree. Otherwise stable_node is the chain and
2036	 * stable_node_dup is the dup to replace.
2037	 */
2038	if (stable_node_dup == stable_node) {
2039		VM_BUG_ON(is_stable_node_dup(stable_node_dup));
2040		/* chain is missing so create it */
2041		stable_node = alloc_stable_node_chain(stable_node_dup,
2042						      root);
2043		if (!stable_node)
2044			return NULL;
2045	}
2046	/*
2047	 * Add this stable_node dup that was
2048	 * migrated to the stable_node chain
2049	 * of the current nid for this page
2050	 * content.
2051	 */
2052	VM_BUG_ON(!is_stable_node_dup(stable_node_dup));
2053	VM_BUG_ON(page_node->head != &migrate_nodes);
2054	list_del(&page_node->list);
2055	DO_NUMA(page_node->nid = nid);
2056	stable_node_chain_add_dup(page_node, stable_node);
2057	goto out;
2058}
2059
2060/*
2061 * stable_tree_insert - insert stable tree node pointing to new ksm page
2062 * into the stable tree.
2063 *
2064 * This function returns the stable tree node just allocated on success,
2065 * NULL otherwise.
2066 */
2067static struct ksm_stable_node *stable_tree_insert(struct page *kpage)
2068{
2069	int nid;
2070	unsigned long kpfn;
2071	struct rb_root *root;
2072	struct rb_node **new;
2073	struct rb_node *parent;
2074	struct ksm_stable_node *stable_node, *stable_node_dup, *stable_node_any;
2075	bool need_chain = false;
2076
2077	kpfn = page_to_pfn(kpage);
2078	nid = get_kpfn_nid(kpfn);
2079	root = root_stable_tree + nid;
2080again:
2081	parent = NULL;
2082	new = &root->rb_node;
2083
2084	while (*new) {
2085		struct page *tree_page;
2086		int ret;
2087
2088		cond_resched();
2089		stable_node = rb_entry(*new, struct ksm_stable_node, node);
2090		stable_node_any = NULL;
2091		tree_page = chain(&stable_node_dup, stable_node, root);
2092		if (!stable_node_dup) {
2093			/*
2094			 * Either all stable_node dups were full in
2095			 * this stable_node chain, or this chain was
2096			 * empty and should be rb_erased.
2097			 */
2098			stable_node_any = stable_node_dup_any(stable_node,
2099							      root);
2100			if (!stable_node_any) {
2101				/* rb_erase just run */
2102				goto again;
2103			}
2104			/*
2105			 * Take any of the stable_node dups page of
2106			 * this stable_node chain to let the tree walk
2107			 * continue. All KSM pages belonging to the
2108			 * stable_node dups in a stable_node chain
2109			 * have the same content and they're
2110			 * write protected at all times. Any will work
2111			 * fine to continue the walk.
2112			 */
2113			tree_page = get_ksm_page(stable_node_any,
2114						 GET_KSM_PAGE_NOLOCK);
2115		}
2116		VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
2117		if (!tree_page) {
2118			/*
2119			 * If we walked over a stale stable_node,
2120			 * get_ksm_page() will call rb_erase() and it
2121			 * may rebalance the tree from under us. So
2122			 * restart the search from scratch. Returning
2123			 * NULL would be safe too, but we'd generate
2124			 * false negative insertions just because some
2125			 * stable_node was stale.
2126			 */
2127			goto again;
2128		}
2129
2130		ret = memcmp_pages(kpage, tree_page);
2131		put_page(tree_page);
2132
2133		parent = *new;
2134		if (ret < 0)
2135			new = &parent->rb_left;
2136		else if (ret > 0)
2137			new = &parent->rb_right;
2138		else {
2139			need_chain = true;
2140			break;
 
 
 
 
2141		}
2142	}
2143
2144	stable_node_dup = alloc_stable_node();
2145	if (!stable_node_dup)
2146		return NULL;
2147
2148	INIT_HLIST_HEAD(&stable_node_dup->hlist);
2149	stable_node_dup->kpfn = kpfn;
2150	set_page_stable_node(kpage, stable_node_dup);
2151	stable_node_dup->rmap_hlist_len = 0;
2152	DO_NUMA(stable_node_dup->nid = nid);
2153	if (!need_chain) {
2154		rb_link_node(&stable_node_dup->node, parent, new);
2155		rb_insert_color(&stable_node_dup->node, root);
2156	} else {
2157		if (!is_stable_node_chain(stable_node)) {
2158			struct ksm_stable_node *orig = stable_node;
2159			/* chain is missing so create it */
2160			stable_node = alloc_stable_node_chain(orig, root);
2161			if (!stable_node) {
2162				free_stable_node(stable_node_dup);
2163				return NULL;
2164			}
2165		}
2166		stable_node_chain_add_dup(stable_node_dup, stable_node);
2167	}
2168
2169	return stable_node_dup;
2170}
2171
2172/*
2173 * unstable_tree_search_insert - search for identical page,
2174 * else insert rmap_item into the unstable tree.
2175 *
2176 * This function searches for a page in the unstable tree identical to the
2177 * page currently being scanned; and if no identical page is found in the
2178 * tree, we insert rmap_item as a new object into the unstable tree.
2179 *
2180 * This function returns pointer to rmap_item found to be identical
2181 * to the currently scanned page, NULL otherwise.
2182 *
2183 * This function does both searching and inserting, because they share
2184 * the same walking algorithm in an rbtree.
2185 */
2186static
2187struct ksm_rmap_item *unstable_tree_search_insert(struct ksm_rmap_item *rmap_item,
2188					      struct page *page,
2189					      struct page **tree_pagep)
 
2190{
2191	struct rb_node **new;
2192	struct rb_root *root;
2193	struct rb_node *parent = NULL;
2194	int nid;
2195
2196	nid = get_kpfn_nid(page_to_pfn(page));
2197	root = root_unstable_tree + nid;
2198	new = &root->rb_node;
2199
2200	while (*new) {
2201		struct ksm_rmap_item *tree_rmap_item;
2202		struct page *tree_page;
2203		int ret;
2204
2205		cond_resched();
2206		tree_rmap_item = rb_entry(*new, struct ksm_rmap_item, node);
2207		tree_page = get_mergeable_page(tree_rmap_item);
2208		if (!tree_page)
2209			return NULL;
2210
2211		/*
2212		 * Don't substitute a ksm page for a forked page.
2213		 */
2214		if (page == tree_page) {
2215			put_page(tree_page);
2216			return NULL;
2217		}
2218
2219		ret = memcmp_pages(page, tree_page);
2220
2221		parent = *new;
2222		if (ret < 0) {
2223			put_page(tree_page);
2224			new = &parent->rb_left;
2225		} else if (ret > 0) {
2226			put_page(tree_page);
2227			new = &parent->rb_right;
2228		} else if (!ksm_merge_across_nodes &&
2229			   page_to_nid(tree_page) != nid) {
2230			/*
2231			 * If tree_page has been migrated to another NUMA node,
2232			 * it will be flushed out and put in the right unstable
2233			 * tree next time: only merge with it when across_nodes.
2234			 */
2235			put_page(tree_page);
2236			return NULL;
2237		} else {
2238			*tree_pagep = tree_page;
2239			return tree_rmap_item;
2240		}
2241	}
2242
2243	rmap_item->address |= UNSTABLE_FLAG;
2244	rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
2245	DO_NUMA(rmap_item->nid = nid);
2246	rb_link_node(&rmap_item->node, parent, new);
2247	rb_insert_color(&rmap_item->node, root);
2248
2249	ksm_pages_unshared++;
2250	return NULL;
2251}
2252
2253/*
2254 * stable_tree_append - add another rmap_item to the linked list of
2255 * rmap_items hanging off a given node of the stable tree, all sharing
2256 * the same ksm page.
2257 */
2258static void stable_tree_append(struct ksm_rmap_item *rmap_item,
2259			       struct ksm_stable_node *stable_node,
2260			       bool max_page_sharing_bypass)
2261{
2262	/*
2263	 * rmap won't find this mapping if we don't insert the
2264	 * rmap_item in the right stable_node
2265	 * duplicate. page_migration could break later if rmap breaks,
2266	 * so we can as well crash here. We really need to check for
2267	 * rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check
2268	 * for other negative values as an underflow if detected here
2269	 * for the first time (and not when decreasing rmap_hlist_len)
2270	 * would be sign of memory corruption in the stable_node.
2271	 */
2272	BUG_ON(stable_node->rmap_hlist_len < 0);
2273
2274	stable_node->rmap_hlist_len++;
2275	if (!max_page_sharing_bypass)
2276		/* possibly non fatal but unexpected overflow, only warn */
2277		WARN_ON_ONCE(stable_node->rmap_hlist_len >
2278			     ksm_max_page_sharing);
2279
2280	rmap_item->head = stable_node;
2281	rmap_item->address |= STABLE_FLAG;
2282	hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
2283
2284	if (rmap_item->hlist.next)
2285		ksm_pages_sharing++;
2286	else
2287		ksm_pages_shared++;
2288
2289	rmap_item->mm->ksm_merging_pages++;
2290}
2291
2292/*
2293 * cmp_and_merge_page - first see if page can be merged into the stable tree;
2294 * if not, compare checksum to previous and if it's the same, see if page can
2295 * be inserted into the unstable tree, or merged with a page already there and
2296 * both transferred to the stable tree.
2297 *
2298 * @page: the page that we are searching identical page to.
2299 * @rmap_item: the reverse mapping into the virtual address of this page
2300 */
2301static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_item)
2302{
2303	struct mm_struct *mm = rmap_item->mm;
2304	struct ksm_rmap_item *tree_rmap_item;
2305	struct page *tree_page = NULL;
2306	struct ksm_stable_node *stable_node;
2307	struct page *kpage;
2308	unsigned int checksum;
2309	int err;
2310	bool max_page_sharing_bypass = false;
2311
2312	stable_node = page_stable_node(page);
2313	if (stable_node) {
2314		if (stable_node->head != &migrate_nodes &&
2315		    get_kpfn_nid(READ_ONCE(stable_node->kpfn)) !=
2316		    NUMA(stable_node->nid)) {
2317			stable_node_dup_del(stable_node);
2318			stable_node->head = &migrate_nodes;
2319			list_add(&stable_node->list, stable_node->head);
2320		}
2321		if (stable_node->head != &migrate_nodes &&
2322		    rmap_item->head == stable_node)
2323			return;
2324		/*
2325		 * If it's a KSM fork, allow it to go over the sharing limit
2326		 * without warnings.
2327		 */
2328		if (!is_page_sharing_candidate(stable_node))
2329			max_page_sharing_bypass = true;
2330	}
2331
2332	/* We first start with searching the page inside the stable tree */
2333	kpage = stable_tree_search(page);
2334	if (kpage == page && rmap_item->head == stable_node) {
2335		put_page(kpage);
2336		return;
2337	}
2338
2339	remove_rmap_item_from_tree(rmap_item);
2340
2341	if (kpage) {
2342		if (PTR_ERR(kpage) == -EBUSY)
2343			return;
2344
2345		err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
2346		if (!err) {
2347			/*
2348			 * The page was successfully merged:
2349			 * add its rmap_item to the stable tree.
2350			 */
2351			lock_page(kpage);
2352			stable_tree_append(rmap_item, page_stable_node(kpage),
2353					   max_page_sharing_bypass);
2354			unlock_page(kpage);
2355		}
2356		put_page(kpage);
2357		return;
2358	}
2359
2360	/*
2361	 * If the hash value of the page has changed from the last time
2362	 * we calculated it, this page is changing frequently: therefore we
2363	 * don't want to insert it in the unstable tree, and we don't want
2364	 * to waste our time searching for something identical to it there.
2365	 */
2366	checksum = calc_checksum(page);
2367	if (rmap_item->oldchecksum != checksum) {
2368		rmap_item->oldchecksum = checksum;
2369		return;
2370	}
2371
2372	/*
2373	 * Same checksum as an empty page. We attempt to merge it with the
2374	 * appropriate zero page if the user enabled this via sysfs.
2375	 */
2376	if (ksm_use_zero_pages && (checksum == zero_checksum)) {
2377		struct vm_area_struct *vma;
2378
2379		mmap_read_lock(mm);
2380		vma = find_mergeable_vma(mm, rmap_item->address);
2381		if (vma) {
2382			err = try_to_merge_one_page(vma, page,
2383					ZERO_PAGE(rmap_item->address));
2384			trace_ksm_merge_one_page(
2385				page_to_pfn(ZERO_PAGE(rmap_item->address)),
2386				rmap_item, mm, err);
2387		} else {
2388			/*
2389			 * If the vma is out of date, we do not need to
2390			 * continue.
2391			 */
2392			err = 0;
2393		}
2394		mmap_read_unlock(mm);
2395		/*
2396		 * In case of failure, the page was not really empty, so we
2397		 * need to continue. Otherwise we're done.
2398		 */
2399		if (!err)
2400			return;
2401	}
2402	tree_rmap_item =
2403		unstable_tree_search_insert(rmap_item, page, &tree_page);
2404	if (tree_rmap_item) {
2405		bool split;
2406
2407		kpage = try_to_merge_two_pages(rmap_item, page,
2408						tree_rmap_item, tree_page);
 
2409		/*
2410		 * If both pages we tried to merge belong to the same compound
2411		 * page, then we actually ended up increasing the reference
2412		 * count of the same compound page twice, and split_huge_page
2413		 * failed.
2414		 * Here we set a flag if that happened, and we use it later to
2415		 * try split_huge_page again. Since we call put_page right
2416		 * afterwards, the reference count will be correct and
2417		 * split_huge_page should succeed.
2418		 */
2419		split = PageTransCompound(page)
2420			&& compound_head(page) == compound_head(tree_page);
2421		put_page(tree_page);
2422		if (kpage) {
2423			/*
2424			 * The pages were successfully merged: insert new
2425			 * node in the stable tree and add both rmap_items.
2426			 */
2427			lock_page(kpage);
2428			stable_node = stable_tree_insert(kpage);
2429			if (stable_node) {
2430				stable_tree_append(tree_rmap_item, stable_node,
2431						   false);
2432				stable_tree_append(rmap_item, stable_node,
2433						   false);
2434			}
2435			unlock_page(kpage);
2436
2437			/*
2438			 * If we fail to insert the page into the stable tree,
2439			 * we will have 2 virtual addresses that are pointing
2440			 * to a ksm page left outside the stable tree,
2441			 * in which case we need to break_cow on both.
2442			 */
2443			if (!stable_node) {
2444				break_cow(tree_rmap_item);
2445				break_cow(rmap_item);
2446			}
2447		} else if (split) {
2448			/*
2449			 * We are here if we tried to merge two pages and
2450			 * failed because they both belonged to the same
2451			 * compound page. We will split the page now, but no
2452			 * merging will take place.
2453			 * We do not want to add the cost of a full lock; if
2454			 * the page is locked, it is better to skip it and
2455			 * perhaps try again later.
2456			 */
2457			if (!trylock_page(page))
2458				return;
2459			split_huge_page(page);
2460			unlock_page(page);
2461		}
2462	}
2463}
2464
2465static struct ksm_rmap_item *get_next_rmap_item(struct ksm_mm_slot *mm_slot,
2466					    struct ksm_rmap_item **rmap_list,
2467					    unsigned long addr)
2468{
2469	struct ksm_rmap_item *rmap_item;
2470
2471	while (*rmap_list) {
2472		rmap_item = *rmap_list;
2473		if ((rmap_item->address & PAGE_MASK) == addr)
2474			return rmap_item;
2475		if (rmap_item->address > addr)
2476			break;
2477		*rmap_list = rmap_item->rmap_list;
2478		remove_rmap_item_from_tree(rmap_item);
2479		free_rmap_item(rmap_item);
2480	}
2481
2482	rmap_item = alloc_rmap_item();
2483	if (rmap_item) {
2484		/* It has already been zeroed */
2485		rmap_item->mm = mm_slot->slot.mm;
2486		rmap_item->mm->ksm_rmap_items++;
2487		rmap_item->address = addr;
2488		rmap_item->rmap_list = *rmap_list;
2489		*rmap_list = rmap_item;
2490	}
2491	return rmap_item;
2492}
2493
2494/*
2495 * Calculate skip age for the ksm page age. The age determines how often
2496 * de-duplicating has already been tried unsuccessfully. If the age is
2497 * smaller, the scanning of this page is skipped for less scans.
2498 *
2499 * @age: rmap_item age of page
2500 */
2501static unsigned int skip_age(rmap_age_t age)
2502{
2503	if (age <= 3)
2504		return 1;
2505	if (age <= 5)
2506		return 2;
2507	if (age <= 8)
2508		return 4;
2509
2510	return 8;
2511}
2512
2513/*
2514 * Determines if a page should be skipped for the current scan.
2515 *
2516 * @page: page to check
2517 * @rmap_item: associated rmap_item of page
2518 */
2519static bool should_skip_rmap_item(struct page *page,
2520				  struct ksm_rmap_item *rmap_item)
2521{
2522	rmap_age_t age;
2523
2524	if (!ksm_smart_scan)
2525		return false;
2526
2527	/*
2528	 * Never skip pages that are already KSM; pages cmp_and_merge_page()
2529	 * will essentially ignore them, but we still have to process them
2530	 * properly.
2531	 */
2532	if (PageKsm(page))
2533		return false;
2534
2535	age = rmap_item->age;
2536	if (age != U8_MAX)
2537		rmap_item->age++;
2538
2539	/*
2540	 * Smaller ages are not skipped, they need to get a chance to go
2541	 * through the different phases of the KSM merging.
2542	 */
2543	if (age < 3)
2544		return false;
2545
2546	/*
2547	 * Are we still allowed to skip? If not, then don't skip it
2548	 * and determine how much more often we are allowed to skip next.
2549	 */
2550	if (!rmap_item->remaining_skips) {
2551		rmap_item->remaining_skips = skip_age(age);
2552		return false;
2553	}
2554
2555	/* Skip this page */
2556	ksm_pages_skipped++;
2557	rmap_item->remaining_skips--;
2558	remove_rmap_item_from_tree(rmap_item);
2559	return true;
2560}
2561
2562static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
2563{
2564	struct mm_struct *mm;
2565	struct ksm_mm_slot *mm_slot;
2566	struct mm_slot *slot;
2567	struct vm_area_struct *vma;
2568	struct ksm_rmap_item *rmap_item;
2569	struct vma_iterator vmi;
2570	int nid;
2571
2572	if (list_empty(&ksm_mm_head.slot.mm_node))
2573		return NULL;
2574
2575	mm_slot = ksm_scan.mm_slot;
2576	if (mm_slot == &ksm_mm_head) {
2577		advisor_start_scan();
2578		trace_ksm_start_scan(ksm_scan.seqnr, ksm_rmap_items);
2579
2580		/*
2581		 * A number of pages can hang around indefinitely in per-cpu
2582		 * LRU cache, raised page count preventing write_protect_page
2583		 * from merging them.  Though it doesn't really matter much,
2584		 * it is puzzling to see some stuck in pages_volatile until
2585		 * other activity jostles them out, and they also prevented
2586		 * LTP's KSM test from succeeding deterministically; so drain
2587		 * them here (here rather than on entry to ksm_do_scan(),
2588		 * so we don't IPI too often when pages_to_scan is set low).
2589		 */
2590		lru_add_drain_all();
2591
2592		/*
2593		 * Whereas stale stable_nodes on the stable_tree itself
2594		 * get pruned in the regular course of stable_tree_search(),
2595		 * those moved out to the migrate_nodes list can accumulate:
2596		 * so prune them once before each full scan.
2597		 */
2598		if (!ksm_merge_across_nodes) {
2599			struct ksm_stable_node *stable_node, *next;
2600			struct page *page;
2601
2602			list_for_each_entry_safe(stable_node, next,
2603						 &migrate_nodes, list) {
2604				page = get_ksm_page(stable_node,
2605						    GET_KSM_PAGE_NOLOCK);
2606				if (page)
2607					put_page(page);
2608				cond_resched();
2609			}
2610		}
2611
2612		for (nid = 0; nid < ksm_nr_node_ids; nid++)
2613			root_unstable_tree[nid] = RB_ROOT;
2614
2615		spin_lock(&ksm_mmlist_lock);
2616		slot = list_entry(mm_slot->slot.mm_node.next,
2617				  struct mm_slot, mm_node);
2618		mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
2619		ksm_scan.mm_slot = mm_slot;
2620		spin_unlock(&ksm_mmlist_lock);
2621		/*
2622		 * Although we tested list_empty() above, a racing __ksm_exit
2623		 * of the last mm on the list may have removed it since then.
2624		 */
2625		if (mm_slot == &ksm_mm_head)
2626			return NULL;
2627next_mm:
2628		ksm_scan.address = 0;
2629		ksm_scan.rmap_list = &mm_slot->rmap_list;
2630	}
2631
2632	slot = &mm_slot->slot;
2633	mm = slot->mm;
2634	vma_iter_init(&vmi, mm, ksm_scan.address);
2635
2636	mmap_read_lock(mm);
2637	if (ksm_test_exit(mm))
2638		goto no_vmas;
 
 
2639
2640	for_each_vma(vmi, vma) {
2641		if (!(vma->vm_flags & VM_MERGEABLE))
2642			continue;
2643		if (ksm_scan.address < vma->vm_start)
2644			ksm_scan.address = vma->vm_start;
2645		if (!vma->anon_vma)
2646			ksm_scan.address = vma->vm_end;
2647
2648		while (ksm_scan.address < vma->vm_end) {
2649			if (ksm_test_exit(mm))
2650				break;
2651			*page = follow_page(vma, ksm_scan.address, FOLL_GET);
2652			if (IS_ERR_OR_NULL(*page)) {
2653				ksm_scan.address += PAGE_SIZE;
2654				cond_resched();
2655				continue;
2656			}
2657			if (is_zone_device_page(*page))
2658				goto next_page;
2659			if (PageAnon(*page)) {
2660				flush_anon_page(vma, *page, ksm_scan.address);
2661				flush_dcache_page(*page);
2662				rmap_item = get_next_rmap_item(mm_slot,
2663					ksm_scan.rmap_list, ksm_scan.address);
2664				if (rmap_item) {
2665					ksm_scan.rmap_list =
2666							&rmap_item->rmap_list;
2667
2668					if (should_skip_rmap_item(*page, rmap_item))
2669						goto next_page;
2670
2671					ksm_scan.address += PAGE_SIZE;
2672				} else
2673					put_page(*page);
2674				mmap_read_unlock(mm);
2675				return rmap_item;
2676			}
2677next_page:
2678			put_page(*page);
2679			ksm_scan.address += PAGE_SIZE;
2680			cond_resched();
2681		}
2682	}
2683
2684	if (ksm_test_exit(mm)) {
2685no_vmas:
2686		ksm_scan.address = 0;
2687		ksm_scan.rmap_list = &mm_slot->rmap_list;
2688	}
2689	/*
2690	 * Nuke all the rmap_items that are above this current rmap:
2691	 * because there were no VM_MERGEABLE vmas with such addresses.
2692	 */
2693	remove_trailing_rmap_items(ksm_scan.rmap_list);
2694
2695	spin_lock(&ksm_mmlist_lock);
2696	slot = list_entry(mm_slot->slot.mm_node.next,
2697			  struct mm_slot, mm_node);
2698	ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
2699	if (ksm_scan.address == 0) {
2700		/*
2701		 * We've completed a full scan of all vmas, holding mmap_lock
2702		 * throughout, and found no VM_MERGEABLE: so do the same as
2703		 * __ksm_exit does to remove this mm from all our lists now.
2704		 * This applies either when cleaning up after __ksm_exit
2705		 * (but beware: we can reach here even before __ksm_exit),
2706		 * or when all VM_MERGEABLE areas have been unmapped (and
2707		 * mmap_lock then protects against race with MADV_MERGEABLE).
2708		 */
2709		hash_del(&mm_slot->slot.hash);
2710		list_del(&mm_slot->slot.mm_node);
2711		spin_unlock(&ksm_mmlist_lock);
2712
2713		mm_slot_free(mm_slot_cache, mm_slot);
2714		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
2715		clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
2716		mmap_read_unlock(mm);
2717		mmdrop(mm);
2718	} else {
2719		mmap_read_unlock(mm);
2720		/*
2721		 * mmap_read_unlock(mm) first because after
2722		 * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
2723		 * already have been freed under us by __ksm_exit()
2724		 * because the "mm_slot" is still hashed and
2725		 * ksm_scan.mm_slot doesn't point to it anymore.
2726		 */
2727		spin_unlock(&ksm_mmlist_lock);
 
2728	}
2729
2730	/* Repeat until we've completed scanning the whole list */
2731	mm_slot = ksm_scan.mm_slot;
2732	if (mm_slot != &ksm_mm_head)
2733		goto next_mm;
2734
2735	advisor_stop_scan();
2736
2737	trace_ksm_stop_scan(ksm_scan.seqnr, ksm_rmap_items);
2738	ksm_scan.seqnr++;
2739	return NULL;
2740}
2741
2742/**
2743 * ksm_do_scan  - the ksm scanner main worker function.
2744 * @scan_npages:  number of pages we want to scan before we return.
2745 */
2746static void ksm_do_scan(unsigned int scan_npages)
2747{
2748	struct ksm_rmap_item *rmap_item;
2749	struct page *page;
2750	unsigned int npages = scan_npages;
2751
2752	while (npages-- && likely(!freezing(current))) {
2753		cond_resched();
2754		rmap_item = scan_get_next_rmap_item(&page);
2755		if (!rmap_item)
2756			return;
2757		cmp_and_merge_page(page, rmap_item);
 
2758		put_page(page);
2759	}
2760
2761	ksm_pages_scanned += scan_npages - npages;
2762}
2763
2764static int ksmd_should_run(void)
2765{
2766	return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.slot.mm_node);
2767}
2768
2769static int ksm_scan_thread(void *nothing)
2770{
2771	unsigned int sleep_ms;
2772
2773	set_freezable();
2774	set_user_nice(current, 5);
2775
2776	while (!kthread_should_stop()) {
2777		mutex_lock(&ksm_thread_mutex);
2778		wait_while_offlining();
2779		if (ksmd_should_run())
2780			ksm_do_scan(ksm_thread_pages_to_scan);
2781		mutex_unlock(&ksm_thread_mutex);
2782
 
 
2783		if (ksmd_should_run()) {
2784			sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs);
2785			wait_event_freezable_timeout(ksm_iter_wait,
2786				sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs),
2787				msecs_to_jiffies(sleep_ms));
2788		} else {
2789			wait_event_freezable(ksm_thread_wait,
2790				ksmd_should_run() || kthread_should_stop());
2791		}
2792	}
2793	return 0;
2794}
2795
2796static void __ksm_add_vma(struct vm_area_struct *vma)
2797{
2798	unsigned long vm_flags = vma->vm_flags;
2799
2800	if (vm_flags & VM_MERGEABLE)
2801		return;
2802
2803	if (vma_ksm_compatible(vma))
2804		vm_flags_set(vma, VM_MERGEABLE);
2805}
2806
2807static int __ksm_del_vma(struct vm_area_struct *vma)
2808{
2809	int err;
2810
2811	if (!(vma->vm_flags & VM_MERGEABLE))
2812		return 0;
2813
2814	if (vma->anon_vma) {
2815		err = unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end, true);
2816		if (err)
2817			return err;
2818	}
2819
2820	vm_flags_clear(vma, VM_MERGEABLE);
2821	return 0;
2822}
2823/**
2824 * ksm_add_vma - Mark vma as mergeable if compatible
2825 *
2826 * @vma:  Pointer to vma
2827 */
2828void ksm_add_vma(struct vm_area_struct *vma)
2829{
2830	struct mm_struct *mm = vma->vm_mm;
2831
2832	if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
2833		__ksm_add_vma(vma);
2834}
2835
2836static void ksm_add_vmas(struct mm_struct *mm)
2837{
2838	struct vm_area_struct *vma;
2839
2840	VMA_ITERATOR(vmi, mm, 0);
2841	for_each_vma(vmi, vma)
2842		__ksm_add_vma(vma);
2843}
2844
2845static int ksm_del_vmas(struct mm_struct *mm)
2846{
2847	struct vm_area_struct *vma;
2848	int err;
2849
2850	VMA_ITERATOR(vmi, mm, 0);
2851	for_each_vma(vmi, vma) {
2852		err = __ksm_del_vma(vma);
2853		if (err)
2854			return err;
2855	}
2856	return 0;
2857}
2858
2859/**
2860 * ksm_enable_merge_any - Add mm to mm ksm list and enable merging on all
2861 *                        compatible VMA's
2862 *
2863 * @mm:  Pointer to mm
2864 *
2865 * Returns 0 on success, otherwise error code
2866 */
2867int ksm_enable_merge_any(struct mm_struct *mm)
2868{
2869	int err;
2870
2871	if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
2872		return 0;
2873
2874	if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
2875		err = __ksm_enter(mm);
2876		if (err)
2877			return err;
2878	}
2879
2880	set_bit(MMF_VM_MERGE_ANY, &mm->flags);
2881	ksm_add_vmas(mm);
2882
2883	return 0;
2884}
2885
2886/**
2887 * ksm_disable_merge_any - Disable merging on all compatible VMA's of the mm,
2888 *			   previously enabled via ksm_enable_merge_any().
2889 *
2890 * Disabling merging implies unmerging any merged pages, like setting
2891 * MADV_UNMERGEABLE would. If unmerging fails, the whole operation fails and
2892 * merging on all compatible VMA's remains enabled.
2893 *
2894 * @mm: Pointer to mm
2895 *
2896 * Returns 0 on success, otherwise error code
2897 */
2898int ksm_disable_merge_any(struct mm_struct *mm)
2899{
2900	int err;
2901
2902	if (!test_bit(MMF_VM_MERGE_ANY, &mm->flags))
2903		return 0;
2904
2905	err = ksm_del_vmas(mm);
2906	if (err) {
2907		ksm_add_vmas(mm);
2908		return err;
2909	}
2910
2911	clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
2912	return 0;
2913}
2914
2915int ksm_disable(struct mm_struct *mm)
2916{
2917	mmap_assert_write_locked(mm);
2918
2919	if (!test_bit(MMF_VM_MERGEABLE, &mm->flags))
2920		return 0;
2921	if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
2922		return ksm_disable_merge_any(mm);
2923	return ksm_del_vmas(mm);
2924}
2925
2926int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
2927		unsigned long end, int advice, unsigned long *vm_flags)
2928{
2929	struct mm_struct *mm = vma->vm_mm;
2930	int err;
2931
2932	switch (advice) {
2933	case MADV_MERGEABLE:
2934		if (vma->vm_flags & VM_MERGEABLE)
2935			return 0;
2936		if (!vma_ksm_compatible(vma))
2937			return 0;
 
 
 
 
2938
2939		if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
2940			err = __ksm_enter(mm);
2941			if (err)
2942				return err;
2943		}
2944
2945		*vm_flags |= VM_MERGEABLE;
2946		break;
2947
2948	case MADV_UNMERGEABLE:
2949		if (!(*vm_flags & VM_MERGEABLE))
2950			return 0;		/* just ignore the advice */
2951
2952		if (vma->anon_vma) {
2953			err = unmerge_ksm_pages(vma, start, end, true);
2954			if (err)
2955				return err;
2956		}
2957
2958		*vm_flags &= ~VM_MERGEABLE;
2959		break;
2960	}
2961
2962	return 0;
2963}
2964EXPORT_SYMBOL_GPL(ksm_madvise);
2965
2966int __ksm_enter(struct mm_struct *mm)
2967{
2968	struct ksm_mm_slot *mm_slot;
2969	struct mm_slot *slot;
2970	int needs_wakeup;
2971
2972	mm_slot = mm_slot_alloc(mm_slot_cache);
2973	if (!mm_slot)
2974		return -ENOMEM;
2975
2976	slot = &mm_slot->slot;
2977
2978	/* Check ksm_run too?  Would need tighter locking */
2979	needs_wakeup = list_empty(&ksm_mm_head.slot.mm_node);
2980
2981	spin_lock(&ksm_mmlist_lock);
2982	mm_slot_insert(mm_slots_hash, mm, slot);
2983	/*
2984	 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
2985	 * insert just behind the scanning cursor, to let the area settle
2986	 * down a little; when fork is followed by immediate exec, we don't
2987	 * want ksmd to waste time setting up and tearing down an rmap_list.
2988	 *
2989	 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
2990	 * scanning cursor, otherwise KSM pages in newly forked mms will be
2991	 * missed: then we might as well insert at the end of the list.
2992	 */
2993	if (ksm_run & KSM_RUN_UNMERGE)
2994		list_add_tail(&slot->mm_node, &ksm_mm_head.slot.mm_node);
2995	else
2996		list_add_tail(&slot->mm_node, &ksm_scan.mm_slot->slot.mm_node);
2997	spin_unlock(&ksm_mmlist_lock);
2998
2999	set_bit(MMF_VM_MERGEABLE, &mm->flags);
3000	mmgrab(mm);
3001
3002	if (needs_wakeup)
3003		wake_up_interruptible(&ksm_thread_wait);
3004
3005	trace_ksm_enter(mm);
3006	return 0;
3007}
3008
3009void __ksm_exit(struct mm_struct *mm)
3010{
3011	struct ksm_mm_slot *mm_slot;
3012	struct mm_slot *slot;
3013	int easy_to_free = 0;
3014
3015	/*
3016	 * This process is exiting: if it's straightforward (as is the
3017	 * case when ksmd was never running), free mm_slot immediately.
3018	 * But if it's at the cursor or has rmap_items linked to it, use
3019	 * mmap_lock to synchronize with any break_cows before pagetables
3020	 * are freed, and leave the mm_slot on the list for ksmd to free.
3021	 * Beware: ksm may already have noticed it exiting and freed the slot.
3022	 */
3023
3024	spin_lock(&ksm_mmlist_lock);
3025	slot = mm_slot_lookup(mm_slots_hash, mm);
3026	mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
3027	if (mm_slot && ksm_scan.mm_slot != mm_slot) {
3028		if (!mm_slot->rmap_list) {
3029			hash_del(&slot->hash);
3030			list_del(&slot->mm_node);
3031			easy_to_free = 1;
3032		} else {
3033			list_move(&slot->mm_node,
3034				  &ksm_scan.mm_slot->slot.mm_node);
3035		}
3036	}
3037	spin_unlock(&ksm_mmlist_lock);
3038
3039	if (easy_to_free) {
3040		mm_slot_free(mm_slot_cache, mm_slot);
3041		clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
3042		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
3043		mmdrop(mm);
3044	} else if (mm_slot) {
3045		mmap_write_lock(mm);
3046		mmap_write_unlock(mm);
3047	}
 
 
 
 
 
 
 
 
 
 
3048
3049	trace_ksm_exit(mm);
3050}
 
 
3051
3052struct folio *ksm_might_need_to_copy(struct folio *folio,
3053			struct vm_area_struct *vma, unsigned long addr)
3054{
3055	struct page *page = folio_page(folio, 0);
3056	struct anon_vma *anon_vma = folio_anon_vma(folio);
3057	struct folio *new_folio;
3058
3059	if (folio_test_large(folio))
3060		return folio;
3061
3062	if (folio_test_ksm(folio)) {
3063		if (folio_stable_node(folio) &&
3064		    !(ksm_run & KSM_RUN_UNMERGE))
3065			return folio;	/* no need to copy it */
3066	} else if (!anon_vma) {
3067		return folio;		/* no need to copy it */
3068	} else if (folio->index == linear_page_index(vma, addr) &&
3069			anon_vma->root == vma->anon_vma->root) {
3070		return folio;		/* still no need to copy it */
3071	}
3072	if (PageHWPoison(page))
3073		return ERR_PTR(-EHWPOISON);
3074	if (!folio_test_uptodate(folio))
3075		return folio;		/* let do_swap_page report the error */
3076
3077	new_folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, addr, false);
3078	if (new_folio &&
3079	    mem_cgroup_charge(new_folio, vma->vm_mm, GFP_KERNEL)) {
3080		folio_put(new_folio);
3081		new_folio = NULL;
3082	}
3083	if (new_folio) {
3084		if (copy_mc_user_highpage(folio_page(new_folio, 0), page,
3085								addr, vma)) {
3086			folio_put(new_folio);
3087			memory_failure_queue(folio_pfn(folio), 0);
3088			return ERR_PTR(-EHWPOISON);
3089		}
3090		folio_set_dirty(new_folio);
3091		__folio_mark_uptodate(new_folio);
3092		__folio_set_locked(new_folio);
3093#ifdef CONFIG_SWAP
3094		count_vm_event(KSM_SWPIN_COPY);
3095#endif
3096	}
3097
3098	return new_folio;
3099}
3100
3101void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc)
 
3102{
3103	struct ksm_stable_node *stable_node;
3104	struct ksm_rmap_item *rmap_item;
 
 
 
3105	int search_new_forks = 0;
3106
3107	VM_BUG_ON_FOLIO(!folio_test_ksm(folio), folio);
 
3108
3109	/*
3110	 * Rely on the page lock to protect against concurrent modifications
3111	 * to that page's node of the stable tree.
3112	 */
3113	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
3114
3115	stable_node = folio_stable_node(folio);
3116	if (!stable_node)
3117		return;
3118again:
3119	hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
3120		struct anon_vma *anon_vma = rmap_item->anon_vma;
3121		struct anon_vma_chain *vmac;
3122		struct vm_area_struct *vma;
3123
3124		cond_resched();
3125		if (!anon_vma_trylock_read(anon_vma)) {
3126			if (rwc->try_lock) {
3127				rwc->contended = true;
3128				return;
3129			}
3130			anon_vma_lock_read(anon_vma);
3131		}
3132		anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
3133					       0, ULONG_MAX) {
3134			unsigned long addr;
3135
3136			cond_resched();
3137			vma = vmac->vma;
3138
3139			/* Ignore the stable/unstable/sqnr flags */
3140			addr = rmap_item->address & PAGE_MASK;
3141
3142			if (addr < vma->vm_start || addr >= vma->vm_end)
3143				continue;
3144			/*
3145			 * Initially we examine only the vma which covers this
3146			 * rmap_item; but later, if there is still work to do,
3147			 * we examine covering vmas in other mms: in case they
3148			 * were forked from the original since ksmd passed.
3149			 */
3150			if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
3151				continue;
3152
3153			if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
3154				continue;
3155
3156			if (!rwc->rmap_one(folio, vma, addr, rwc->arg)) {
3157				anon_vma_unlock_read(anon_vma);
3158				return;
3159			}
3160			if (rwc->done && rwc->done(folio)) {
3161				anon_vma_unlock_read(anon_vma);
3162				return;
3163			}
3164		}
3165		anon_vma_unlock_read(anon_vma);
 
 
3166	}
3167	if (!search_new_forks++)
3168		goto again;
 
 
3169}
3170
3171#ifdef CONFIG_MEMORY_FAILURE
3172/*
3173 * Collect processes when the error hit an ksm page.
3174 */
3175void collect_procs_ksm(struct page *page, struct list_head *to_kill,
3176		       int force_early)
3177{
3178	struct ksm_stable_node *stable_node;
3179	struct ksm_rmap_item *rmap_item;
3180	struct folio *folio = page_folio(page);
3181	struct vm_area_struct *vma;
3182	struct task_struct *tsk;
 
 
 
3183
3184	stable_node = folio_stable_node(folio);
3185	if (!stable_node)
3186		return;
3187	hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
3188		struct anon_vma *av = rmap_item->anon_vma;
 
 
 
3189
3190		anon_vma_lock_read(av);
3191		rcu_read_lock();
3192		for_each_process(tsk) {
3193			struct anon_vma_chain *vmac;
3194			unsigned long addr;
3195			struct task_struct *t =
3196				task_early_kill(tsk, force_early);
3197			if (!t)
3198				continue;
3199			anon_vma_interval_tree_foreach(vmac, &av->rb_root, 0,
3200						       ULONG_MAX)
3201			{
3202				vma = vmac->vma;
3203				if (vma->vm_mm == t->mm) {
3204					addr = rmap_item->address & PAGE_MASK;
3205					add_to_kill_ksm(t, page, vma, to_kill,
3206							addr);
3207				}
 
 
 
 
 
3208			}
3209		}
3210		rcu_read_unlock();
3211		anon_vma_unlock_read(av);
3212	}
 
 
 
 
3213}
3214#endif
3215
3216#ifdef CONFIG_MIGRATION
3217void folio_migrate_ksm(struct folio *newfolio, struct folio *folio)
 
3218{
3219	struct ksm_stable_node *stable_node;
 
 
 
 
3220
3221	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
3222	VM_BUG_ON_FOLIO(!folio_test_locked(newfolio), newfolio);
3223	VM_BUG_ON_FOLIO(newfolio->mapping != folio->mapping, newfolio);
3224
3225	stable_node = folio_stable_node(folio);
3226	if (stable_node) {
3227		VM_BUG_ON_FOLIO(stable_node->kpfn != folio_pfn(folio), folio);
3228		stable_node->kpfn = folio_pfn(newfolio);
3229		/*
3230		 * newfolio->mapping was set in advance; now we need smp_wmb()
3231		 * to make sure that the new stable_node->kpfn is visible
3232		 * to get_ksm_page() before it can see that folio->mapping
3233		 * has gone stale (or that folio_test_swapcache has been cleared).
3234		 */
3235		smp_wmb();
3236		set_page_stable_node(&folio->page, NULL);
3237	}
3238}
3239#endif /* CONFIG_MIGRATION */
3240
3241#ifdef CONFIG_MEMORY_HOTREMOVE
3242static void wait_while_offlining(void)
3243{
3244	while (ksm_run & KSM_RUN_OFFLINE) {
3245		mutex_unlock(&ksm_thread_mutex);
3246		wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
3247			    TASK_UNINTERRUPTIBLE);
3248		mutex_lock(&ksm_thread_mutex);
3249	}
3250}
 
 
 
 
3251
3252static bool stable_node_dup_remove_range(struct ksm_stable_node *stable_node,
3253					 unsigned long start_pfn,
3254					 unsigned long end_pfn)
3255{
3256	if (stable_node->kpfn >= start_pfn &&
3257	    stable_node->kpfn < end_pfn) {
3258		/*
3259		 * Don't get_ksm_page, page has already gone:
3260		 * which is why we keep kpfn instead of page*
3261		 */
3262		remove_node_from_stable_tree(stable_node);
3263		return true;
3264	}
3265	return false;
 
 
 
3266}
3267
3268static bool stable_node_chain_remove_range(struct ksm_stable_node *stable_node,
3269					   unsigned long start_pfn,
3270					   unsigned long end_pfn,
3271					   struct rb_root *root)
3272{
3273	struct ksm_stable_node *dup;
3274	struct hlist_node *hlist_safe;
3275
3276	if (!is_stable_node_chain(stable_node)) {
3277		VM_BUG_ON(is_stable_node_dup(stable_node));
3278		return stable_node_dup_remove_range(stable_node, start_pfn,
3279						    end_pfn);
3280	}
3281
3282	hlist_for_each_entry_safe(dup, hlist_safe,
3283				  &stable_node->hlist, hlist_dup) {
3284		VM_BUG_ON(!is_stable_node_dup(dup));
3285		stable_node_dup_remove_range(dup, start_pfn, end_pfn);
3286	}
3287	if (hlist_empty(&stable_node->hlist)) {
3288		free_stable_node_chain(stable_node, root);
3289		return true; /* notify caller that tree was rebalanced */
3290	} else
3291		return false;
3292}
 
3293
3294static void ksm_check_stable_tree(unsigned long start_pfn,
3295				  unsigned long end_pfn)
 
3296{
3297	struct ksm_stable_node *stable_node, *next;
3298	struct rb_node *node;
3299	int nid;
3300
3301	for (nid = 0; nid < ksm_nr_node_ids; nid++) {
3302		node = rb_first(root_stable_tree + nid);
3303		while (node) {
3304			stable_node = rb_entry(node, struct ksm_stable_node, node);
3305			if (stable_node_chain_remove_range(stable_node,
3306							   start_pfn, end_pfn,
3307							   root_stable_tree +
3308							   nid))
3309				node = rb_first(root_stable_tree + nid);
3310			else
3311				node = rb_next(node);
3312			cond_resched();
3313		}
3314	}
3315	list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
3316		if (stable_node->kpfn >= start_pfn &&
3317		    stable_node->kpfn < end_pfn)
3318			remove_node_from_stable_tree(stable_node);
3319		cond_resched();
3320	}
 
3321}
3322
3323static int ksm_memory_callback(struct notifier_block *self,
3324			       unsigned long action, void *arg)
3325{
3326	struct memory_notify *mn = arg;
 
3327
3328	switch (action) {
3329	case MEM_GOING_OFFLINE:
3330		/*
3331		 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
3332		 * and remove_all_stable_nodes() while memory is going offline:
3333		 * it is unsafe for them to touch the stable tree at this time.
3334		 * But unmerge_ksm_pages(), rmap lookups and other entry points
3335		 * which do not need the ksm_thread_mutex are all safe.
 
 
3336		 */
3337		mutex_lock(&ksm_thread_mutex);
3338		ksm_run |= KSM_RUN_OFFLINE;
3339		mutex_unlock(&ksm_thread_mutex);
3340		break;
3341
3342	case MEM_OFFLINE:
3343		/*
3344		 * Most of the work is done by page migration; but there might
3345		 * be a few stable_nodes left over, still pointing to struct
3346		 * pages which have been offlined: prune those from the tree,
3347		 * otherwise get_ksm_page() might later try to access a
3348		 * non-existent struct page.
3349		 */
3350		ksm_check_stable_tree(mn->start_pfn,
3351				      mn->start_pfn + mn->nr_pages);
3352		fallthrough;
 
 
3353	case MEM_CANCEL_OFFLINE:
3354		mutex_lock(&ksm_thread_mutex);
3355		ksm_run &= ~KSM_RUN_OFFLINE;
3356		mutex_unlock(&ksm_thread_mutex);
3357
3358		smp_mb();	/* wake_up_bit advises this */
3359		wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
3360		break;
3361	}
3362	return NOTIFY_OK;
3363}
3364#else
3365static void wait_while_offlining(void)
3366{
3367}
3368#endif /* CONFIG_MEMORY_HOTREMOVE */
3369
3370#ifdef CONFIG_PROC_FS
3371long ksm_process_profit(struct mm_struct *mm)
3372{
3373	return (long)(mm->ksm_merging_pages + mm->ksm_zero_pages) * PAGE_SIZE -
3374		mm->ksm_rmap_items * sizeof(struct ksm_rmap_item);
3375}
3376#endif /* CONFIG_PROC_FS */
3377
3378#ifdef CONFIG_SYSFS
3379/*
3380 * This all compiles without CONFIG_SYSFS, but is a waste of space.
3381 */
3382
3383#define KSM_ATTR_RO(_name) \
3384	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
3385#define KSM_ATTR(_name) \
3386	static struct kobj_attribute _name##_attr = __ATTR_RW(_name)
 
3387
3388static ssize_t sleep_millisecs_show(struct kobject *kobj,
3389				    struct kobj_attribute *attr, char *buf)
3390{
3391	return sysfs_emit(buf, "%u\n", ksm_thread_sleep_millisecs);
3392}
3393
3394static ssize_t sleep_millisecs_store(struct kobject *kobj,
3395				     struct kobj_attribute *attr,
3396				     const char *buf, size_t count)
3397{
3398	unsigned int msecs;
3399	int err;
3400
3401	err = kstrtouint(buf, 10, &msecs);
3402	if (err)
3403		return -EINVAL;
3404
3405	ksm_thread_sleep_millisecs = msecs;
3406	wake_up_interruptible(&ksm_iter_wait);
3407
3408	return count;
3409}
3410KSM_ATTR(sleep_millisecs);
3411
3412static ssize_t pages_to_scan_show(struct kobject *kobj,
3413				  struct kobj_attribute *attr, char *buf)
3414{
3415	return sysfs_emit(buf, "%u\n", ksm_thread_pages_to_scan);
3416}
3417
3418static ssize_t pages_to_scan_store(struct kobject *kobj,
3419				   struct kobj_attribute *attr,
3420				   const char *buf, size_t count)
3421{
3422	unsigned int nr_pages;
3423	int err;
 
3424
3425	if (ksm_advisor != KSM_ADVISOR_NONE)
3426		return -EINVAL;
3427
3428	err = kstrtouint(buf, 10, &nr_pages);
3429	if (err)
3430		return -EINVAL;
3431
3432	ksm_thread_pages_to_scan = nr_pages;
3433
3434	return count;
3435}
3436KSM_ATTR(pages_to_scan);
3437
3438static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
3439			char *buf)
3440{
3441	return sysfs_emit(buf, "%lu\n", ksm_run);
3442}
3443
3444static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
3445			 const char *buf, size_t count)
3446{
3447	unsigned int flags;
3448	int err;
 
3449
3450	err = kstrtouint(buf, 10, &flags);
3451	if (err)
3452		return -EINVAL;
3453	if (flags > KSM_RUN_UNMERGE)
3454		return -EINVAL;
3455
3456	/*
3457	 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
3458	 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
3459	 * breaking COW to free the pages_shared (but leaves mm_slots
3460	 * on the list for when ksmd may be set running again).
3461	 */
3462
3463	mutex_lock(&ksm_thread_mutex);
3464	wait_while_offlining();
3465	if (ksm_run != flags) {
3466		ksm_run = flags;
3467		if (flags & KSM_RUN_UNMERGE) {
3468			set_current_oom_origin();
 
 
3469			err = unmerge_and_remove_all_rmap_items();
3470			clear_current_oom_origin();
3471			if (err) {
3472				ksm_run = KSM_RUN_STOP;
3473				count = err;
3474			}
3475		}
3476	}
3477	mutex_unlock(&ksm_thread_mutex);
3478
3479	if (flags & KSM_RUN_MERGE)
3480		wake_up_interruptible(&ksm_thread_wait);
3481
3482	return count;
3483}
3484KSM_ATTR(run);
3485
3486#ifdef CONFIG_NUMA
3487static ssize_t merge_across_nodes_show(struct kobject *kobj,
3488				       struct kobj_attribute *attr, char *buf)
3489{
3490	return sysfs_emit(buf, "%u\n", ksm_merge_across_nodes);
3491}
3492
3493static ssize_t merge_across_nodes_store(struct kobject *kobj,
3494				   struct kobj_attribute *attr,
3495				   const char *buf, size_t count)
3496{
3497	int err;
3498	unsigned long knob;
3499
3500	err = kstrtoul(buf, 10, &knob);
3501	if (err)
3502		return err;
3503	if (knob > 1)
3504		return -EINVAL;
3505
3506	mutex_lock(&ksm_thread_mutex);
3507	wait_while_offlining();
3508	if (ksm_merge_across_nodes != knob) {
3509		if (ksm_pages_shared || remove_all_stable_nodes())
3510			err = -EBUSY;
3511		else if (root_stable_tree == one_stable_tree) {
3512			struct rb_root *buf;
3513			/*
3514			 * This is the first time that we switch away from the
3515			 * default of merging across nodes: must now allocate
3516			 * a buffer to hold as many roots as may be needed.
3517			 * Allocate stable and unstable together:
3518			 * MAXSMP NODES_SHIFT 10 will use 16kB.
3519			 */
3520			buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
3521				      GFP_KERNEL);
3522			/* Let us assume that RB_ROOT is NULL is zero */
3523			if (!buf)
3524				err = -ENOMEM;
3525			else {
3526				root_stable_tree = buf;
3527				root_unstable_tree = buf + nr_node_ids;
3528				/* Stable tree is empty but not the unstable */
3529				root_unstable_tree[0] = one_unstable_tree[0];
3530			}
3531		}
3532		if (!err) {
3533			ksm_merge_across_nodes = knob;
3534			ksm_nr_node_ids = knob ? 1 : nr_node_ids;
3535		}
3536	}
3537	mutex_unlock(&ksm_thread_mutex);
3538
3539	return err ? err : count;
3540}
3541KSM_ATTR(merge_across_nodes);
3542#endif
3543
3544static ssize_t use_zero_pages_show(struct kobject *kobj,
3545				   struct kobj_attribute *attr, char *buf)
3546{
3547	return sysfs_emit(buf, "%u\n", ksm_use_zero_pages);
3548}
3549static ssize_t use_zero_pages_store(struct kobject *kobj,
3550				   struct kobj_attribute *attr,
3551				   const char *buf, size_t count)
3552{
3553	int err;
3554	bool value;
3555
3556	err = kstrtobool(buf, &value);
3557	if (err)
3558		return -EINVAL;
3559
3560	ksm_use_zero_pages = value;
3561
3562	return count;
3563}
3564KSM_ATTR(use_zero_pages);
3565
3566static ssize_t max_page_sharing_show(struct kobject *kobj,
3567				     struct kobj_attribute *attr, char *buf)
3568{
3569	return sysfs_emit(buf, "%u\n", ksm_max_page_sharing);
3570}
3571
3572static ssize_t max_page_sharing_store(struct kobject *kobj,
3573				      struct kobj_attribute *attr,
3574				      const char *buf, size_t count)
3575{
3576	int err;
3577	int knob;
3578
3579	err = kstrtoint(buf, 10, &knob);
3580	if (err)
3581		return err;
3582	/*
3583	 * When a KSM page is created it is shared by 2 mappings. This
3584	 * being a signed comparison, it implicitly verifies it's not
3585	 * negative.
3586	 */
3587	if (knob < 2)
3588		return -EINVAL;
3589
3590	if (READ_ONCE(ksm_max_page_sharing) == knob)
3591		return count;
3592
3593	mutex_lock(&ksm_thread_mutex);
3594	wait_while_offlining();
3595	if (ksm_max_page_sharing != knob) {
3596		if (ksm_pages_shared || remove_all_stable_nodes())
3597			err = -EBUSY;
3598		else
3599			ksm_max_page_sharing = knob;
3600	}
3601	mutex_unlock(&ksm_thread_mutex);
3602
3603	return err ? err : count;
3604}
3605KSM_ATTR(max_page_sharing);
3606
3607static ssize_t pages_scanned_show(struct kobject *kobj,
3608				  struct kobj_attribute *attr, char *buf)
3609{
3610	return sysfs_emit(buf, "%lu\n", ksm_pages_scanned);
3611}
3612KSM_ATTR_RO(pages_scanned);
3613
3614static ssize_t pages_shared_show(struct kobject *kobj,
3615				 struct kobj_attribute *attr, char *buf)
3616{
3617	return sysfs_emit(buf, "%lu\n", ksm_pages_shared);
3618}
3619KSM_ATTR_RO(pages_shared);
3620
3621static ssize_t pages_sharing_show(struct kobject *kobj,
3622				  struct kobj_attribute *attr, char *buf)
3623{
3624	return sysfs_emit(buf, "%lu\n", ksm_pages_sharing);
3625}
3626KSM_ATTR_RO(pages_sharing);
3627
3628static ssize_t pages_unshared_show(struct kobject *kobj,
3629				   struct kobj_attribute *attr, char *buf)
3630{
3631	return sysfs_emit(buf, "%lu\n", ksm_pages_unshared);
3632}
3633KSM_ATTR_RO(pages_unshared);
3634
3635static ssize_t pages_volatile_show(struct kobject *kobj,
3636				   struct kobj_attribute *attr, char *buf)
3637{
3638	long ksm_pages_volatile;
3639
3640	ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
3641				- ksm_pages_sharing - ksm_pages_unshared;
3642	/*
3643	 * It was not worth any locking to calculate that statistic,
3644	 * but it might therefore sometimes be negative: conceal that.
3645	 */
3646	if (ksm_pages_volatile < 0)
3647		ksm_pages_volatile = 0;
3648	return sysfs_emit(buf, "%ld\n", ksm_pages_volatile);
3649}
3650KSM_ATTR_RO(pages_volatile);
3651
3652static ssize_t pages_skipped_show(struct kobject *kobj,
3653				  struct kobj_attribute *attr, char *buf)
3654{
3655	return sysfs_emit(buf, "%lu\n", ksm_pages_skipped);
3656}
3657KSM_ATTR_RO(pages_skipped);
3658
3659static ssize_t ksm_zero_pages_show(struct kobject *kobj,
3660				struct kobj_attribute *attr, char *buf)
3661{
3662	return sysfs_emit(buf, "%ld\n", ksm_zero_pages);
3663}
3664KSM_ATTR_RO(ksm_zero_pages);
3665
3666static ssize_t general_profit_show(struct kobject *kobj,
3667				   struct kobj_attribute *attr, char *buf)
3668{
3669	long general_profit;
3670
3671	general_profit = (ksm_pages_sharing + ksm_zero_pages) * PAGE_SIZE -
3672				ksm_rmap_items * sizeof(struct ksm_rmap_item);
3673
3674	return sysfs_emit(buf, "%ld\n", general_profit);
3675}
3676KSM_ATTR_RO(general_profit);
3677
3678static ssize_t stable_node_dups_show(struct kobject *kobj,
3679				     struct kobj_attribute *attr, char *buf)
3680{
3681	return sysfs_emit(buf, "%lu\n", ksm_stable_node_dups);
3682}
3683KSM_ATTR_RO(stable_node_dups);
3684
3685static ssize_t stable_node_chains_show(struct kobject *kobj,
3686				       struct kobj_attribute *attr, char *buf)
3687{
3688	return sysfs_emit(buf, "%lu\n", ksm_stable_node_chains);
3689}
3690KSM_ATTR_RO(stable_node_chains);
3691
3692static ssize_t
3693stable_node_chains_prune_millisecs_show(struct kobject *kobj,
3694					struct kobj_attribute *attr,
3695					char *buf)
3696{
3697	return sysfs_emit(buf, "%u\n", ksm_stable_node_chains_prune_millisecs);
3698}
3699
3700static ssize_t
3701stable_node_chains_prune_millisecs_store(struct kobject *kobj,
3702					 struct kobj_attribute *attr,
3703					 const char *buf, size_t count)
3704{
3705	unsigned int msecs;
3706	int err;
3707
3708	err = kstrtouint(buf, 10, &msecs);
3709	if (err)
3710		return -EINVAL;
3711
3712	ksm_stable_node_chains_prune_millisecs = msecs;
3713
3714	return count;
3715}
3716KSM_ATTR(stable_node_chains_prune_millisecs);
3717
3718static ssize_t full_scans_show(struct kobject *kobj,
3719			       struct kobj_attribute *attr, char *buf)
3720{
3721	return sysfs_emit(buf, "%lu\n", ksm_scan.seqnr);
3722}
3723KSM_ATTR_RO(full_scans);
3724
3725static ssize_t smart_scan_show(struct kobject *kobj,
3726			       struct kobj_attribute *attr, char *buf)
3727{
3728	return sysfs_emit(buf, "%u\n", ksm_smart_scan);
3729}
3730
3731static ssize_t smart_scan_store(struct kobject *kobj,
3732				struct kobj_attribute *attr,
3733				const char *buf, size_t count)
3734{
3735	int err;
3736	bool value;
3737
3738	err = kstrtobool(buf, &value);
3739	if (err)
3740		return -EINVAL;
3741
3742	ksm_smart_scan = value;
3743	return count;
3744}
3745KSM_ATTR(smart_scan);
3746
3747static ssize_t advisor_mode_show(struct kobject *kobj,
3748				 struct kobj_attribute *attr, char *buf)
3749{
3750	const char *output;
3751
3752	if (ksm_advisor == KSM_ADVISOR_NONE)
3753		output = "[none] scan-time";
3754	else if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
3755		output = "none [scan-time]";
3756
3757	return sysfs_emit(buf, "%s\n", output);
3758}
3759
3760static ssize_t advisor_mode_store(struct kobject *kobj,
3761				  struct kobj_attribute *attr, const char *buf,
3762				  size_t count)
3763{
3764	enum ksm_advisor_type curr_advisor = ksm_advisor;
3765
3766	if (sysfs_streq("scan-time", buf))
3767		ksm_advisor = KSM_ADVISOR_SCAN_TIME;
3768	else if (sysfs_streq("none", buf))
3769		ksm_advisor = KSM_ADVISOR_NONE;
3770	else
3771		return -EINVAL;
3772
3773	/* Set advisor default values */
3774	if (curr_advisor != ksm_advisor)
3775		set_advisor_defaults();
3776
3777	return count;
3778}
3779KSM_ATTR(advisor_mode);
3780
3781static ssize_t advisor_max_cpu_show(struct kobject *kobj,
3782				    struct kobj_attribute *attr, char *buf)
3783{
3784	return sysfs_emit(buf, "%u\n", ksm_advisor_max_cpu);
3785}
3786
3787static ssize_t advisor_max_cpu_store(struct kobject *kobj,
3788				     struct kobj_attribute *attr,
3789				     const char *buf, size_t count)
3790{
3791	int err;
3792	unsigned long value;
3793
3794	err = kstrtoul(buf, 10, &value);
3795	if (err)
3796		return -EINVAL;
3797
3798	ksm_advisor_max_cpu = value;
3799	return count;
3800}
3801KSM_ATTR(advisor_max_cpu);
3802
3803static ssize_t advisor_min_pages_to_scan_show(struct kobject *kobj,
3804					struct kobj_attribute *attr, char *buf)
3805{
3806	return sysfs_emit(buf, "%lu\n", ksm_advisor_min_pages_to_scan);
3807}
3808
3809static ssize_t advisor_min_pages_to_scan_store(struct kobject *kobj,
3810					struct kobj_attribute *attr,
3811					const char *buf, size_t count)
3812{
3813	int err;
3814	unsigned long value;
3815
3816	err = kstrtoul(buf, 10, &value);
3817	if (err)
3818		return -EINVAL;
3819
3820	ksm_advisor_min_pages_to_scan = value;
3821	return count;
3822}
3823KSM_ATTR(advisor_min_pages_to_scan);
3824
3825static ssize_t advisor_max_pages_to_scan_show(struct kobject *kobj,
3826					struct kobj_attribute *attr, char *buf)
3827{
3828	return sysfs_emit(buf, "%lu\n", ksm_advisor_max_pages_to_scan);
3829}
3830
3831static ssize_t advisor_max_pages_to_scan_store(struct kobject *kobj,
3832					struct kobj_attribute *attr,
3833					const char *buf, size_t count)
3834{
3835	int err;
3836	unsigned long value;
3837
3838	err = kstrtoul(buf, 10, &value);
3839	if (err)
3840		return -EINVAL;
3841
3842	ksm_advisor_max_pages_to_scan = value;
3843	return count;
3844}
3845KSM_ATTR(advisor_max_pages_to_scan);
3846
3847static ssize_t advisor_target_scan_time_show(struct kobject *kobj,
3848					     struct kobj_attribute *attr, char *buf)
3849{
3850	return sysfs_emit(buf, "%lu\n", ksm_advisor_target_scan_time);
3851}
3852
3853static ssize_t advisor_target_scan_time_store(struct kobject *kobj,
3854					      struct kobj_attribute *attr,
3855					      const char *buf, size_t count)
3856{
3857	int err;
3858	unsigned long value;
3859
3860	err = kstrtoul(buf, 10, &value);
3861	if (err)
3862		return -EINVAL;
3863	if (value < 1)
3864		return -EINVAL;
3865
3866	ksm_advisor_target_scan_time = value;
3867	return count;
3868}
3869KSM_ATTR(advisor_target_scan_time);
3870
3871static struct attribute *ksm_attrs[] = {
3872	&sleep_millisecs_attr.attr,
3873	&pages_to_scan_attr.attr,
3874	&run_attr.attr,
3875	&pages_scanned_attr.attr,
3876	&pages_shared_attr.attr,
3877	&pages_sharing_attr.attr,
3878	&pages_unshared_attr.attr,
3879	&pages_volatile_attr.attr,
3880	&pages_skipped_attr.attr,
3881	&ksm_zero_pages_attr.attr,
3882	&full_scans_attr.attr,
3883#ifdef CONFIG_NUMA
3884	&merge_across_nodes_attr.attr,
3885#endif
3886	&max_page_sharing_attr.attr,
3887	&stable_node_chains_attr.attr,
3888	&stable_node_dups_attr.attr,
3889	&stable_node_chains_prune_millisecs_attr.attr,
3890	&use_zero_pages_attr.attr,
3891	&general_profit_attr.attr,
3892	&smart_scan_attr.attr,
3893	&advisor_mode_attr.attr,
3894	&advisor_max_cpu_attr.attr,
3895	&advisor_min_pages_to_scan_attr.attr,
3896	&advisor_max_pages_to_scan_attr.attr,
3897	&advisor_target_scan_time_attr.attr,
3898	NULL,
3899};
3900
3901static const struct attribute_group ksm_attr_group = {
3902	.attrs = ksm_attrs,
3903	.name = "ksm",
3904};
3905#endif /* CONFIG_SYSFS */
3906
3907static int __init ksm_init(void)
3908{
3909	struct task_struct *ksm_thread;
3910	int err;
3911
3912	/* The correct value depends on page size and endianness */
3913	zero_checksum = calc_checksum(ZERO_PAGE(0));
3914	/* Default to false for backwards compatibility */
3915	ksm_use_zero_pages = false;
3916
3917	err = ksm_slab_init();
3918	if (err)
3919		goto out;
3920
3921	ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
3922	if (IS_ERR(ksm_thread)) {
3923		pr_err("ksm: creating kthread failed\n");
3924		err = PTR_ERR(ksm_thread);
3925		goto out_free;
3926	}
3927
3928#ifdef CONFIG_SYSFS
3929	err = sysfs_create_group(mm_kobj, &ksm_attr_group);
3930	if (err) {
3931		pr_err("ksm: register sysfs failed\n");
3932		kthread_stop(ksm_thread);
3933		goto out_free;
3934	}
3935#else
3936	ksm_run = KSM_RUN_MERGE;	/* no way for user to start it */
3937
3938#endif /* CONFIG_SYSFS */
3939
3940#ifdef CONFIG_MEMORY_HOTREMOVE
3941	/* There is no significance to this priority 100 */
3942	hotplug_memory_notifier(ksm_memory_callback, KSM_CALLBACK_PRI);
 
 
 
3943#endif
3944	return 0;
3945
3946out_free:
3947	ksm_slab_free();
3948out:
3949	return err;
3950}
3951subsys_initcall(ksm_init);