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