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)