ksm.c 52.7 KB
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/*
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 * Memory merging support.
 *
 * This code enables dynamic sharing of identical pages found in different
 * memory areas, even if they are not shared by fork()
 *
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 * Copyright (C) 2008-2009 Red Hat, Inc.
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 * Authors:
 *	Izik Eidus
 *	Andrea Arcangeli
 *	Chris Wright
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 *	Hugh Dickins
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 *
 * This work is licensed under the terms of the GNU GPL, version 2.
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 */

#include <linux/errno.h>
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#include <linux/mm.h>
#include <linux/fs.h>
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#include <linux/mman.h>
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#include <linux/sched.h>
#include <linux/rwsem.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/spinlock.h>
#include <linux/jhash.h>
#include <linux/delay.h>
#include <linux/kthread.h>
#include <linux/wait.h>
#include <linux/slab.h>
#include <linux/rbtree.h>
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#include <linux/memory.h>
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#include <linux/mmu_notifier.h>
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#include <linux/swap.h>
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#include <linux/ksm.h>

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#include <asm/tlbflush.h>
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#include "internal.h"
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/*
 * A few notes about the KSM scanning process,
 * to make it easier to understand the data structures below:
 *
 * In order to reduce excessive scanning, KSM sorts the memory pages by their
 * contents into a data structure that holds pointers to the pages' locations.
 *
 * Since the contents of the pages may change at any moment, KSM cannot just
 * insert the pages into a normal sorted tree and expect it to find anything.
 * Therefore KSM uses two data structures - the stable and the unstable tree.
 *
 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
 * by their contents.  Because each such page is write-protected, searching on
 * this tree is fully assured to be working (except when pages are unmapped),
 * and therefore this tree is called the stable tree.
 *
 * In addition to the stable tree, KSM uses a second data structure called the
 * unstable tree: this tree holds pointers to pages which have been found to
 * be "unchanged for a period of time".  The unstable tree sorts these pages
 * by their contents, but since they are not write-protected, KSM cannot rely
 * upon the unstable tree to work correctly - the unstable tree is liable to
 * be corrupted as its contents are modified, and so it is called unstable.
 *
 * KSM solves this problem by several techniques:
 *
 * 1) The unstable tree is flushed every time KSM completes scanning all
 *    memory areas, and then the tree is rebuilt again from the beginning.
 * 2) KSM will only insert into the unstable tree, pages whose hash value
 *    has not changed since the previous scan of all memory areas.
 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
 *    colors of the nodes and not on their contents, assuring that even when
 *    the tree gets "corrupted" it won't get out of balance, so scanning time
 *    remains the same (also, searching and inserting nodes in an rbtree uses
 *    the same algorithm, so we have no overhead when we flush and rebuild).
 * 4) KSM never flushes the stable tree, which means that even if it were to
 *    take 10 attempts to find a page in the unstable tree, once it is found,
 *    it is secured in the stable tree.  (When we scan a new page, we first
 *    compare it against the stable tree, and then against the unstable tree.)
 */

/**
 * struct mm_slot - ksm information per mm that is being scanned
 * @link: link to the mm_slots hash list
 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
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 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
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 * @mm: the mm that this information is valid for
 */
struct mm_slot {
	struct hlist_node link;
	struct list_head mm_list;
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	struct rmap_item *rmap_list;
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	struct mm_struct *mm;
};

/**
 * struct ksm_scan - cursor for scanning
 * @mm_slot: the current mm_slot we are scanning
 * @address: the next address inside that to be scanned
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 * @rmap_list: link to the next rmap to be scanned in the rmap_list
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 * @seqnr: count of completed full scans (needed when removing unstable node)
 *
 * There is only the one ksm_scan instance of this cursor structure.
 */
struct ksm_scan {
	struct mm_slot *mm_slot;
	unsigned long address;
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	struct rmap_item **rmap_list;
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	unsigned long seqnr;
};

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/**
 * struct stable_node - node of the stable rbtree
 * @node: rb node of this ksm page in the stable tree
 * @hlist: hlist head of rmap_items using this ksm page
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 * @kpfn: page frame number of this ksm page
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 */
struct stable_node {
	struct rb_node node;
	struct hlist_head hlist;
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	unsigned long kpfn;
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};

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/**
 * struct rmap_item - reverse mapping item for virtual addresses
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 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
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 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
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 * @mm: the memory structure this rmap_item is pointing into
 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
 * @oldchecksum: previous checksum of the page at that virtual address
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 * @node: rb node of this rmap_item in the unstable tree
 * @head: pointer to stable_node heading this list in the stable tree
 * @hlist: link into hlist of rmap_items hanging off that stable_node
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 */
struct rmap_item {
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	struct rmap_item *rmap_list;
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	struct anon_vma *anon_vma;	/* when stable */
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	struct mm_struct *mm;
	unsigned long address;		/* + low bits used for flags below */
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	unsigned int oldchecksum;	/* when unstable */
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	union {
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		struct rb_node node;	/* when node of unstable tree */
		struct {		/* when listed from stable tree */
			struct stable_node *head;
			struct hlist_node hlist;
		};
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	};
};

#define SEQNR_MASK	0x0ff	/* low bits of unstable tree seqnr */
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#define UNSTABLE_FLAG	0x100	/* is a node of the unstable tree */
#define STABLE_FLAG	0x200	/* is listed from the stable tree */
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/* The stable and unstable tree heads */
static struct rb_root root_stable_tree = RB_ROOT;
static struct rb_root root_unstable_tree = RB_ROOT;

#define MM_SLOTS_HASH_HEADS 1024
static struct hlist_head *mm_slots_hash;

static struct mm_slot ksm_mm_head = {
	.mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
};
static struct ksm_scan ksm_scan = {
	.mm_slot = &ksm_mm_head,
};

static struct kmem_cache *rmap_item_cache;
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static struct kmem_cache *stable_node_cache;
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static struct kmem_cache *mm_slot_cache;

/* The number of nodes in the stable tree */
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static unsigned long ksm_pages_shared;
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/* The number of page slots additionally sharing those nodes */
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static unsigned long ksm_pages_sharing;
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/* The number of nodes in the unstable tree */
static unsigned long ksm_pages_unshared;

/* The number of rmap_items in use: to calculate pages_volatile */
static unsigned long ksm_rmap_items;

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/* Number of pages ksmd should scan in one batch */
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static unsigned int ksm_thread_pages_to_scan = 100;
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/* Milliseconds ksmd should sleep between batches */
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static unsigned int ksm_thread_sleep_millisecs = 20;
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#define KSM_RUN_STOP	0
#define KSM_RUN_MERGE	1
#define KSM_RUN_UNMERGE	2
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static unsigned int ksm_run = KSM_RUN_STOP;
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static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
static DEFINE_MUTEX(ksm_thread_mutex);
static DEFINE_SPINLOCK(ksm_mmlist_lock);

#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
		sizeof(struct __struct), __alignof__(struct __struct),\
		(__flags), NULL)

static int __init ksm_slab_init(void)
{
	rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
	if (!rmap_item_cache)
		goto out;

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	stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
	if (!stable_node_cache)
		goto out_free1;

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	mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
	if (!mm_slot_cache)
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		goto out_free2;
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	return 0;

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out_free2:
	kmem_cache_destroy(stable_node_cache);
out_free1:
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	kmem_cache_destroy(rmap_item_cache);
out:
	return -ENOMEM;
}

static void __init ksm_slab_free(void)
{
	kmem_cache_destroy(mm_slot_cache);
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	kmem_cache_destroy(stable_node_cache);
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	kmem_cache_destroy(rmap_item_cache);
	mm_slot_cache = NULL;
}

static inline struct rmap_item *alloc_rmap_item(void)
{
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	struct rmap_item *rmap_item;

	rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
	if (rmap_item)
		ksm_rmap_items++;
	return rmap_item;
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}

static inline void free_rmap_item(struct rmap_item *rmap_item)
{
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	ksm_rmap_items--;
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	rmap_item->mm = NULL;	/* debug safety */
	kmem_cache_free(rmap_item_cache, rmap_item);
}

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static inline struct stable_node *alloc_stable_node(void)
{
	return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
}

static inline void free_stable_node(struct stable_node *stable_node)
{
	kmem_cache_free(stable_node_cache, stable_node);
}

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static inline struct mm_slot *alloc_mm_slot(void)
{
	if (!mm_slot_cache)	/* initialization failed */
		return NULL;
	return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
}

static inline void free_mm_slot(struct mm_slot *mm_slot)
{
	kmem_cache_free(mm_slot_cache, mm_slot);
}

static int __init mm_slots_hash_init(void)
{
	mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
				GFP_KERNEL);
	if (!mm_slots_hash)
		return -ENOMEM;
	return 0;
}

static void __init mm_slots_hash_free(void)
{
	kfree(mm_slots_hash);
}

static struct mm_slot *get_mm_slot(struct mm_struct *mm)
{
	struct mm_slot *mm_slot;
	struct hlist_head *bucket;
	struct hlist_node *node;

	bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
				% MM_SLOTS_HASH_HEADS];
	hlist_for_each_entry(mm_slot, node, bucket, link) {
		if (mm == mm_slot->mm)
			return mm_slot;
	}
	return NULL;
}

static void insert_to_mm_slots_hash(struct mm_struct *mm,
				    struct mm_slot *mm_slot)
{
	struct hlist_head *bucket;

	bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
				% MM_SLOTS_HASH_HEADS];
	mm_slot->mm = mm;
	hlist_add_head(&mm_slot->link, bucket);
}

static inline int in_stable_tree(struct rmap_item *rmap_item)
{
	return rmap_item->address & STABLE_FLAG;
}

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static void hold_anon_vma(struct rmap_item *rmap_item,
			  struct anon_vma *anon_vma)
{
	rmap_item->anon_vma = anon_vma;
	atomic_inc(&anon_vma->ksm_refcount);
}

static void drop_anon_vma(struct rmap_item *rmap_item)
{
	struct anon_vma *anon_vma = rmap_item->anon_vma;

	if (atomic_dec_and_lock(&anon_vma->ksm_refcount, &anon_vma->lock)) {
		int empty = list_empty(&anon_vma->head);
		spin_unlock(&anon_vma->lock);
		if (empty)
			anon_vma_free(anon_vma);
	}
}

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/*
 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
 * page tables after it has passed through ksm_exit() - which, if necessary,
 * takes mmap_sem briefly to serialize against them.  ksm_exit() does not set
 * a special flag: they can just back out as soon as mm_users goes to zero.
 * ksm_test_exit() is used throughout to make this test for exit: in some
 * places for correctness, in some places just to avoid unnecessary work.
 */
static inline bool ksm_test_exit(struct mm_struct *mm)
{
	return atomic_read(&mm->mm_users) == 0;
}

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/*
 * We use break_ksm to break COW on a ksm page: it's a stripped down
 *
 *	if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
 *		put_page(page);
 *
 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
 * in case the application has unmapped and remapped mm,addr meanwhile.
 * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
 */
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static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
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{
	struct page *page;
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	int ret = 0;
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	do {
		cond_resched();
		page = follow_page(vma, addr, FOLL_GET);
		if (!page)
			break;
		if (PageKsm(page))
			ret = handle_mm_fault(vma->vm_mm, vma, addr,
							FAULT_FLAG_WRITE);
		else
			ret = VM_FAULT_WRITE;
		put_page(page);
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	} while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
	/*
	 * We must loop because handle_mm_fault() may back out if there's
	 * any difficulty e.g. if pte accessed bit gets updated concurrently.
	 *
	 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
	 * COW has been broken, even if the vma does not permit VM_WRITE;
	 * but note that a concurrent fault might break PageKsm for us.
	 *
	 * VM_FAULT_SIGBUS could occur if we race with truncation of the
	 * backing file, which also invalidates anonymous pages: that's
	 * okay, that truncation will have unmapped the PageKsm for us.
	 *
	 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
	 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
	 * current task has TIF_MEMDIE set, and will be OOM killed on return
	 * to user; and ksmd, having no mm, would never be chosen for that.
	 *
	 * But if the mm is in a limited mem_cgroup, then the fault may fail
	 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
	 * even ksmd can fail in this way - though it's usually breaking ksm
	 * just to undo a merge it made a moment before, so unlikely to oom.
	 *
	 * That's a pity: we might therefore have more kernel pages allocated
	 * than we're counting as nodes in the stable tree; but ksm_do_scan
	 * will retry to break_cow on each pass, so should recover the page
	 * in due course.  The important thing is to not let VM_MERGEABLE
	 * be cleared while any such pages might remain in the area.
	 */
	return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
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}

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static void break_cow(struct rmap_item *rmap_item)
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{
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	struct mm_struct *mm = rmap_item->mm;
	unsigned long addr = rmap_item->address;
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	struct vm_area_struct *vma;

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	/*
	 * It is not an accident that whenever we want to break COW
	 * to undo, we also need to drop a reference to the anon_vma.
	 */
	drop_anon_vma(rmap_item);

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	down_read(&mm->mmap_sem);
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	if (ksm_test_exit(mm))
		goto out;
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	vma = find_vma(mm, addr);
	if (!vma || vma->vm_start > addr)
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		goto out;
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	if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
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		goto out;
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	break_ksm(vma, addr);
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out:
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	up_read(&mm->mmap_sem);
}

static struct page *get_mergeable_page(struct rmap_item *rmap_item)
{
	struct mm_struct *mm = rmap_item->mm;
	unsigned long addr = rmap_item->address;
	struct vm_area_struct *vma;
	struct page *page;

	down_read(&mm->mmap_sem);
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	if (ksm_test_exit(mm))
		goto out;
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	vma = find_vma(mm, addr);
	if (!vma || vma->vm_start > addr)
		goto out;
	if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
		goto out;

	page = follow_page(vma, addr, FOLL_GET);
	if (!page)
		goto out;
	if (PageAnon(page)) {
		flush_anon_page(vma, page, addr);
		flush_dcache_page(page);
	} else {
		put_page(page);
out:		page = NULL;
	}
	up_read(&mm->mmap_sem);
	return page;
}

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static void remove_node_from_stable_tree(struct stable_node *stable_node)
{
	struct rmap_item *rmap_item;
	struct hlist_node *hlist;

	hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
		if (rmap_item->hlist.next)
			ksm_pages_sharing--;
		else
			ksm_pages_shared--;
		drop_anon_vma(rmap_item);
		rmap_item->address &= PAGE_MASK;
		cond_resched();
	}

	rb_erase(&stable_node->node, &root_stable_tree);
	free_stable_node(stable_node);
}

/*
 * get_ksm_page: checks if the page indicated by the stable node
 * is still its ksm page, despite having held no reference to it.
 * In which case we can trust the content of the page, and it
 * returns the gotten page; but if the page has now been zapped,
 * remove the stale node from the stable tree and return NULL.
 *
 * You would expect the stable_node to hold a reference to the ksm page.
 * But if it increments the page's count, swapping out has to wait for
 * ksmd to come around again before it can free the page, which may take
 * seconds or even minutes: much too unresponsive.  So instead we use a
 * "keyhole reference": access to the ksm page from the stable node peeps
 * out through its keyhole to see if that page still holds the right key,
 * pointing back to this stable node.  This relies on freeing a PageAnon
 * page to reset its page->mapping to NULL, and relies on no other use of
 * a page to put something that might look like our key in page->mapping.
 *
 * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
 * but this is different - made simpler by ksm_thread_mutex being held, but
 * interesting for assuming that no other use of the struct page could ever
 * put our expected_mapping into page->mapping (or a field of the union which
 * coincides with page->mapping).  The RCU calls are not for KSM at all, but
 * to keep the page_count protocol described with page_cache_get_speculative.
 *
 * Note: it is possible that get_ksm_page() will return NULL one moment,
 * then page the next, if the page is in between page_freeze_refs() and
 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
 * is on its way to being freed; but it is an anomaly to bear in mind.
 */
static struct page *get_ksm_page(struct stable_node *stable_node)
{
	struct page *page;
	void *expected_mapping;

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	page = pfn_to_page(stable_node->kpfn);
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	expected_mapping = (void *)stable_node +
				(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
	rcu_read_lock();
	if (page->mapping != expected_mapping)
		goto stale;
	if (!get_page_unless_zero(page))
		goto stale;
	if (page->mapping != expected_mapping) {
		put_page(page);
		goto stale;
	}
	rcu_read_unlock();
	return page;
stale:
	rcu_read_unlock();
	remove_node_from_stable_tree(stable_node);
	return NULL;
}

I
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536 537 538 539 540 541
/*
 * Removing rmap_item from stable or unstable tree.
 * This function will clean the information from the stable/unstable tree.
 */
static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
{
H
Hugh Dickins 已提交
542 543
	if (rmap_item->address & STABLE_FLAG) {
		struct stable_node *stable_node;
H
Hugh Dickins 已提交
544
		struct page *page;
I
Izik Eidus 已提交
545

H
Hugh Dickins 已提交
546
		stable_node = rmap_item->head;
H
Hugh Dickins 已提交
547 548 549
		page = get_ksm_page(stable_node);
		if (!page)
			goto out;
H
Hugh Dickins 已提交
550

H
Hugh Dickins 已提交
551
		lock_page(page);
H
Hugh Dickins 已提交
552
		hlist_del(&rmap_item->hlist);
H
Hugh Dickins 已提交
553 554
		unlock_page(page);
		put_page(page);
555

H
Hugh Dickins 已提交
556 557 558
		if (stable_node->hlist.first)
			ksm_pages_sharing--;
		else
H
Hugh Dickins 已提交
559
			ksm_pages_shared--;
I
Izik Eidus 已提交
560

H
Hugh Dickins 已提交
561
		drop_anon_vma(rmap_item);
562
		rmap_item->address &= PAGE_MASK;
I
Izik Eidus 已提交
563

H
Hugh Dickins 已提交
564
	} else if (rmap_item->address & UNSTABLE_FLAG) {
I
Izik Eidus 已提交
565 566
		unsigned char age;
		/*
H
Hugh Dickins 已提交
567
		 * Usually ksmd can and must skip the rb_erase, because
I
Izik Eidus 已提交
568
		 * root_unstable_tree was already reset to RB_ROOT.
H
Hugh Dickins 已提交
569 570 571
		 * But be careful when an mm is exiting: do the rb_erase
		 * if this rmap_item was inserted by this scan, rather
		 * than left over from before.
I
Izik Eidus 已提交
572 573
		 */
		age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
574
		BUG_ON(age > 1);
I
Izik Eidus 已提交
575 576
		if (!age)
			rb_erase(&rmap_item->node, &root_unstable_tree);
577

578
		ksm_pages_unshared--;
579
		rmap_item->address &= PAGE_MASK;
I
Izik Eidus 已提交
580
	}
H
Hugh Dickins 已提交
581
out:
I
Izik Eidus 已提交
582 583 584 585
	cond_resched();		/* we're called from many long loops */
}

static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
H
Hugh Dickins 已提交
586
				       struct rmap_item **rmap_list)
I
Izik Eidus 已提交
587
{
H
Hugh Dickins 已提交
588 589 590
	while (*rmap_list) {
		struct rmap_item *rmap_item = *rmap_list;
		*rmap_list = rmap_item->rmap_list;
I
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591 592 593 594 595 596 597 598 599 600 601 602
		remove_rmap_item_from_tree(rmap_item);
		free_rmap_item(rmap_item);
	}
}

/*
 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
 * than check every pte of a given vma, the locking doesn't quite work for
 * that - an rmap_item is assigned to the stable tree after inserting ksm
 * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
 * rmap_items from parent to child at fork time (so as not to waste time
 * if exit comes before the next scan reaches it).
H
Hugh Dickins 已提交
603 604 605 606 607
 *
 * Similarly, although we'd like to remove rmap_items (so updating counts
 * and freeing memory) when unmerging an area, it's easier to leave that
 * to the next pass of ksmd - consider, for example, how ksmd might be
 * in cmp_and_merge_page on one of the rmap_items we would be removing.
I
Izik Eidus 已提交
608
 */
H
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609 610
static int unmerge_ksm_pages(struct vm_area_struct *vma,
			     unsigned long start, unsigned long end)
I
Izik Eidus 已提交
611 612
{
	unsigned long addr;
H
Hugh Dickins 已提交
613
	int err = 0;
I
Izik Eidus 已提交
614

H
Hugh Dickins 已提交
615
	for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
H
Hugh Dickins 已提交
616 617
		if (ksm_test_exit(vma->vm_mm))
			break;
H
Hugh Dickins 已提交
618 619 620 621 622 623
		if (signal_pending(current))
			err = -ERESTARTSYS;
		else
			err = break_ksm(vma, addr);
	}
	return err;
I
Izik Eidus 已提交
624 625
}

H
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626 627 628 629
#ifdef CONFIG_SYSFS
/*
 * Only called through the sysfs control interface:
 */
H
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630
static int unmerge_and_remove_all_rmap_items(void)
I
Izik Eidus 已提交
631 632 633 634
{
	struct mm_slot *mm_slot;
	struct mm_struct *mm;
	struct vm_area_struct *vma;
H
Hugh Dickins 已提交
635 636 637
	int err = 0;

	spin_lock(&ksm_mmlist_lock);
H
Hugh Dickins 已提交
638
	ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
H
Hugh Dickins 已提交
639 640
						struct mm_slot, mm_list);
	spin_unlock(&ksm_mmlist_lock);
I
Izik Eidus 已提交
641

H
Hugh Dickins 已提交
642 643
	for (mm_slot = ksm_scan.mm_slot;
			mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
I
Izik Eidus 已提交
644 645 646
		mm = mm_slot->mm;
		down_read(&mm->mmap_sem);
		for (vma = mm->mmap; vma; vma = vma->vm_next) {
H
Hugh Dickins 已提交
647 648
			if (ksm_test_exit(mm))
				break;
I
Izik Eidus 已提交
649 650
			if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
				continue;
H
Hugh Dickins 已提交
651 652
			err = unmerge_ksm_pages(vma,
						vma->vm_start, vma->vm_end);
H
Hugh Dickins 已提交
653 654
			if (err)
				goto error;
I
Izik Eidus 已提交
655
		}
H
Hugh Dickins 已提交
656

H
Hugh Dickins 已提交
657
		remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
H
Hugh Dickins 已提交
658 659

		spin_lock(&ksm_mmlist_lock);
H
Hugh Dickins 已提交
660
		ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
H
Hugh Dickins 已提交
661
						struct mm_slot, mm_list);
H
Hugh Dickins 已提交
662 663 664 665 666 667 668 669 670 671 672 673 674
		if (ksm_test_exit(mm)) {
			hlist_del(&mm_slot->link);
			list_del(&mm_slot->mm_list);
			spin_unlock(&ksm_mmlist_lock);

			free_mm_slot(mm_slot);
			clear_bit(MMF_VM_MERGEABLE, &mm->flags);
			up_read(&mm->mmap_sem);
			mmdrop(mm);
		} else {
			spin_unlock(&ksm_mmlist_lock);
			up_read(&mm->mmap_sem);
		}
I
Izik Eidus 已提交
675 676
	}

H
Hugh Dickins 已提交
677
	ksm_scan.seqnr = 0;
H
Hugh Dickins 已提交
678 679 680 681
	return 0;

error:
	up_read(&mm->mmap_sem);
I
Izik Eidus 已提交
682
	spin_lock(&ksm_mmlist_lock);
H
Hugh Dickins 已提交
683
	ksm_scan.mm_slot = &ksm_mm_head;
I
Izik Eidus 已提交
684
	spin_unlock(&ksm_mmlist_lock);
H
Hugh Dickins 已提交
685
	return err;
I
Izik Eidus 已提交
686
}
H
Hugh Dickins 已提交
687
#endif /* CONFIG_SYSFS */
I
Izik Eidus 已提交
688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752

static u32 calc_checksum(struct page *page)
{
	u32 checksum;
	void *addr = kmap_atomic(page, KM_USER0);
	checksum = jhash2(addr, PAGE_SIZE / 4, 17);
	kunmap_atomic(addr, KM_USER0);
	return checksum;
}

static int memcmp_pages(struct page *page1, struct page *page2)
{
	char *addr1, *addr2;
	int ret;

	addr1 = kmap_atomic(page1, KM_USER0);
	addr2 = kmap_atomic(page2, KM_USER1);
	ret = memcmp(addr1, addr2, PAGE_SIZE);
	kunmap_atomic(addr2, KM_USER1);
	kunmap_atomic(addr1, KM_USER0);
	return ret;
}

static inline int pages_identical(struct page *page1, struct page *page2)
{
	return !memcmp_pages(page1, page2);
}

static int write_protect_page(struct vm_area_struct *vma, struct page *page,
			      pte_t *orig_pte)
{
	struct mm_struct *mm = vma->vm_mm;
	unsigned long addr;
	pte_t *ptep;
	spinlock_t *ptl;
	int swapped;
	int err = -EFAULT;

	addr = page_address_in_vma(page, vma);
	if (addr == -EFAULT)
		goto out;

	ptep = page_check_address(page, mm, addr, &ptl, 0);
	if (!ptep)
		goto out;

	if (pte_write(*ptep)) {
		pte_t entry;

		swapped = PageSwapCache(page);
		flush_cache_page(vma, addr, page_to_pfn(page));
		/*
		 * Ok this is tricky, when get_user_pages_fast() run it doesnt
		 * take any lock, therefore the check that we are going to make
		 * with the pagecount against the mapcount is racey and
		 * O_DIRECT can happen right after the check.
		 * So we clear the pte and flush the tlb before the check
		 * this assure us that no O_DIRECT can happen after the check
		 * or in the middle of the check.
		 */
		entry = ptep_clear_flush(vma, addr, ptep);
		/*
		 * Check that no O_DIRECT or similar I/O is in progress on the
		 * page
		 */
753
		if (page_mapcount(page) + 1 + swapped != page_count(page)) {
I
Izik Eidus 已提交
754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770
			set_pte_at_notify(mm, addr, ptep, entry);
			goto out_unlock;
		}
		entry = pte_wrprotect(entry);
		set_pte_at_notify(mm, addr, ptep, entry);
	}
	*orig_pte = *ptep;
	err = 0;

out_unlock:
	pte_unmap_unlock(ptep, ptl);
out:
	return err;
}

/**
 * replace_page - replace page in vma by new ksm page
771 772 773
 * @vma:      vma that holds the pte pointing to page
 * @page:     the page we are replacing by kpage
 * @kpage:    the ksm page we replace page by
I
Izik Eidus 已提交
774 775 776 777
 * @orig_pte: the original value of the pte
 *
 * Returns 0 on success, -EFAULT on failure.
 */
778 779
static int replace_page(struct vm_area_struct *vma, struct page *page,
			struct page *kpage, pte_t orig_pte)
I
Izik Eidus 已提交
780 781 782 783 784 785 786 787 788 789
{
	struct mm_struct *mm = vma->vm_mm;
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *ptep;
	spinlock_t *ptl;
	unsigned long addr;
	int err = -EFAULT;

790
	addr = page_address_in_vma(page, vma);
I
Izik Eidus 已提交
791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811
	if (addr == -EFAULT)
		goto out;

	pgd = pgd_offset(mm, addr);
	if (!pgd_present(*pgd))
		goto out;

	pud = pud_offset(pgd, addr);
	if (!pud_present(*pud))
		goto out;

	pmd = pmd_offset(pud, addr);
	if (!pmd_present(*pmd))
		goto out;

	ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
	if (!pte_same(*ptep, orig_pte)) {
		pte_unmap_unlock(ptep, ptl);
		goto out;
	}

812
	get_page(kpage);
H
Hugh Dickins 已提交
813
	page_add_anon_rmap(kpage, vma, addr);
I
Izik Eidus 已提交
814 815 816

	flush_cache_page(vma, addr, pte_pfn(*ptep));
	ptep_clear_flush(vma, addr, ptep);
817
	set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
I
Izik Eidus 已提交
818

819 820
	page_remove_rmap(page);
	put_page(page);
I
Izik Eidus 已提交
821 822 823 824 825 826 827 828 829

	pte_unmap_unlock(ptep, ptl);
	err = 0;
out:
	return err;
}

/*
 * try_to_merge_one_page - take two pages and merge them into one
830 831
 * @vma: the vma that holds the pte pointing to page
 * @page: the PageAnon page that we want to replace with kpage
832 833
 * @kpage: the PageKsm page that we want to map instead of page,
 *         or NULL the first time when we want to use page as kpage.
I
Izik Eidus 已提交
834 835 836 837
 *
 * This function returns 0 if the pages were merged, -EFAULT otherwise.
 */
static int try_to_merge_one_page(struct vm_area_struct *vma,
838
				 struct page *page, struct page *kpage)
I
Izik Eidus 已提交
839 840 841 842
{
	pte_t orig_pte = __pte(0);
	int err = -EFAULT;

H
Hugh Dickins 已提交
843 844 845
	if (page == kpage)			/* ksm page forked */
		return 0;

I
Izik Eidus 已提交
846 847
	if (!(vma->vm_flags & VM_MERGEABLE))
		goto out;
848
	if (!PageAnon(page))
I
Izik Eidus 已提交
849 850 851 852 853 854 855 856 857
		goto out;

	/*
	 * We need the page lock to read a stable PageSwapCache in
	 * write_protect_page().  We use trylock_page() instead of
	 * lock_page() because we don't want to wait here - we
	 * prefer to continue scanning and merging different pages,
	 * then come back to this page when it is unlocked.
	 */
858
	if (!trylock_page(page))
859
		goto out;
I
Izik Eidus 已提交
860 861 862 863 864 865
	/*
	 * If this anonymous page is mapped only here, its pte may need
	 * to be write-protected.  If it's mapped elsewhere, all of its
	 * ptes are necessarily already write-protected.  But in either
	 * case, we need to lock and check page_count is not raised.
	 */
866 867 868 869 870 871 872 873 874 875 876 877 878
	if (write_protect_page(vma, page, &orig_pte) == 0) {
		if (!kpage) {
			/*
			 * While we hold page lock, upgrade page from
			 * PageAnon+anon_vma to PageKsm+NULL stable_node:
			 * stable_tree_insert() will update stable_node.
			 */
			set_page_stable_node(page, NULL);
			mark_page_accessed(page);
			err = 0;
		} else if (pages_identical(page, kpage))
			err = replace_page(vma, page, kpage, orig_pte);
	}
I
Izik Eidus 已提交
879

880
	if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
H
Hugh Dickins 已提交
881
		munlock_vma_page(page);
H
Hugh Dickins 已提交
882 883 884 885 886 887 888
		if (!PageMlocked(kpage)) {
			unlock_page(page);
			lock_page(kpage);
			mlock_vma_page(kpage);
			page = kpage;		/* for final unlock */
		}
	}
H
Hugh Dickins 已提交
889

890
	unlock_page(page);
I
Izik Eidus 已提交
891 892 893 894
out:
	return err;
}

H
Hugh Dickins 已提交
895 896 897
/*
 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
 * but no new kernel page is allocated: kpage must already be a ksm page.
898 899
 *
 * This function returns 0 if the pages were merged, -EFAULT otherwise.
H
Hugh Dickins 已提交
900
 */
901 902
static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
				      struct page *page, struct page *kpage)
H
Hugh Dickins 已提交
903
{
904
	struct mm_struct *mm = rmap_item->mm;
H
Hugh Dickins 已提交
905 906 907
	struct vm_area_struct *vma;
	int err = -EFAULT;

908 909
	down_read(&mm->mmap_sem);
	if (ksm_test_exit(mm))
H
Hugh Dickins 已提交
910
		goto out;
911 912
	vma = find_vma(mm, rmap_item->address);
	if (!vma || vma->vm_start > rmap_item->address)
H
Hugh Dickins 已提交
913 914
		goto out;

915
	err = try_to_merge_one_page(vma, page, kpage);
H
Hugh Dickins 已提交
916 917 918 919 920
	if (err)
		goto out;

	/* Must get reference to anon_vma while still holding mmap_sem */
	hold_anon_vma(rmap_item, vma->anon_vma);
H
Hugh Dickins 已提交
921
out:
922
	up_read(&mm->mmap_sem);
H
Hugh Dickins 已提交
923 924 925
	return err;
}

I
Izik Eidus 已提交
926 927 928 929
/*
 * try_to_merge_two_pages - take two identical pages and prepare them
 * to be merged into one page.
 *
930 931
 * This function returns the kpage if we successfully merged two identical
 * pages into one ksm page, NULL otherwise.
I
Izik Eidus 已提交
932
 *
933
 * Note that this function upgrades page to ksm page: if one of the pages
I
Izik Eidus 已提交
934 935
 * is already a ksm page, try_to_merge_with_ksm_page should be used.
 */
936 937 938 939
static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
					   struct page *page,
					   struct rmap_item *tree_rmap_item,
					   struct page *tree_page)
I
Izik Eidus 已提交
940
{
941
	int err;
I
Izik Eidus 已提交
942

943
	err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
I
Izik Eidus 已提交
944
	if (!err) {
945
		err = try_to_merge_with_ksm_page(tree_rmap_item,
946
							tree_page, page);
I
Izik Eidus 已提交
947
		/*
H
Hugh Dickins 已提交
948 949
		 * If that fails, we have a ksm page with only one pte
		 * pointing to it: so break it.
I
Izik Eidus 已提交
950
		 */
H
Hugh Dickins 已提交
951
		if (err)
952
			break_cow(rmap_item);
I
Izik Eidus 已提交
953
	}
954
	return err ? NULL : page;
I
Izik Eidus 已提交
955 956 957
}

/*
958
 * stable_tree_search - search for page inside the stable tree
I
Izik Eidus 已提交
959 960 961 962
 *
 * This function checks if there is a page inside the stable tree
 * with identical content to the page that we are scanning right now.
 *
H
Hugh Dickins 已提交
963
 * This function returns the stable tree node of identical content if found,
I
Izik Eidus 已提交
964 965
 * NULL otherwise.
 */
966
static struct page *stable_tree_search(struct page *page)
I
Izik Eidus 已提交
967 968
{
	struct rb_node *node = root_stable_tree.rb_node;
H
Hugh Dickins 已提交
969
	struct stable_node *stable_node;
I
Izik Eidus 已提交
970

971 972 973
	stable_node = page_stable_node(page);
	if (stable_node) {			/* ksm page forked */
		get_page(page);
974
		return page;
975 976
	}

I
Izik Eidus 已提交
977
	while (node) {
H
Hugh Dickins 已提交
978
		struct page *tree_page;
I
Izik Eidus 已提交
979 980
		int ret;

981
		cond_resched();
H
Hugh Dickins 已提交
982
		stable_node = rb_entry(node, struct stable_node, node);
H
Hugh Dickins 已提交
983 984 985
		tree_page = get_ksm_page(stable_node);
		if (!tree_page)
			return NULL;
I
Izik Eidus 已提交
986

H
Hugh Dickins 已提交
987
		ret = memcmp_pages(page, tree_page);
I
Izik Eidus 已提交
988

H
Hugh Dickins 已提交
989 990
		if (ret < 0) {
			put_page(tree_page);
I
Izik Eidus 已提交
991
			node = node->rb_left;
H
Hugh Dickins 已提交
992 993
		} else if (ret > 0) {
			put_page(tree_page);
I
Izik Eidus 已提交
994
			node = node->rb_right;
H
Hugh Dickins 已提交
995
		} else
996
			return tree_page;
I
Izik Eidus 已提交
997 998 999 1000 1001 1002 1003 1004 1005
	}

	return NULL;
}

/*
 * stable_tree_insert - insert rmap_item pointing to new ksm page
 * into the stable tree.
 *
H
Hugh Dickins 已提交
1006 1007
 * This function returns the stable tree node just allocated on success,
 * NULL otherwise.
I
Izik Eidus 已提交
1008
 */
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static struct stable_node *stable_tree_insert(struct page *kpage)
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1010 1011 1012
{
	struct rb_node **new = &root_stable_tree.rb_node;
	struct rb_node *parent = NULL;
H
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	struct stable_node *stable_node;
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1014 1015

	while (*new) {
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1016
		struct page *tree_page;
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1017 1018
		int ret;

1019
		cond_resched();
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1020
		stable_node = rb_entry(*new, struct stable_node, node);
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1021 1022 1023
		tree_page = get_ksm_page(stable_node);
		if (!tree_page)
			return NULL;
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1024

H
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1025 1026
		ret = memcmp_pages(kpage, tree_page);
		put_page(tree_page);
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1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042

		parent = *new;
		if (ret < 0)
			new = &parent->rb_left;
		else if (ret > 0)
			new = &parent->rb_right;
		else {
			/*
			 * It is not a bug that stable_tree_search() didn't
			 * find this node: because at that time our page was
			 * not yet write-protected, so may have changed since.
			 */
			return NULL;
		}
	}

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1043 1044 1045
	stable_node = alloc_stable_node();
	if (!stable_node)
		return NULL;
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1046

H
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1047 1048 1049 1050 1051
	rb_link_node(&stable_node->node, parent, new);
	rb_insert_color(&stable_node->node, &root_stable_tree);

	INIT_HLIST_HEAD(&stable_node->hlist);

1052
	stable_node->kpfn = page_to_pfn(kpage);
1053 1054
	set_page_stable_node(kpage, stable_node);

H
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1055
	return stable_node;
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1056 1057 1058
}

/*
1059 1060
 * unstable_tree_search_insert - search for identical page,
 * else insert rmap_item into the unstable tree.
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1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071
 *
 * This function searches for a page in the unstable tree identical to the
 * page currently being scanned; and if no identical page is found in the
 * tree, we insert rmap_item as a new object into the unstable tree.
 *
 * This function returns pointer to rmap_item found to be identical
 * to the currently scanned page, NULL otherwise.
 *
 * This function does both searching and inserting, because they share
 * the same walking algorithm in an rbtree.
 */
1072 1073 1074 1075 1076
static
struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
					      struct page *page,
					      struct page **tree_pagep)

I
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1077 1078 1079 1080 1081 1082
{
	struct rb_node **new = &root_unstable_tree.rb_node;
	struct rb_node *parent = NULL;

	while (*new) {
		struct rmap_item *tree_rmap_item;
1083
		struct page *tree_page;
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1084 1085
		int ret;

H
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1086
		cond_resched();
I
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1087
		tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1088 1089
		tree_page = get_mergeable_page(tree_rmap_item);
		if (!tree_page)
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1090 1091 1092
			return NULL;

		/*
1093
		 * Don't substitute a ksm page for a forked page.
I
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1094
		 */
1095 1096
		if (page == tree_page) {
			put_page(tree_page);
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1097 1098 1099
			return NULL;
		}

1100
		ret = memcmp_pages(page, tree_page);
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1101 1102 1103

		parent = *new;
		if (ret < 0) {
1104
			put_page(tree_page);
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1105 1106
			new = &parent->rb_left;
		} else if (ret > 0) {
1107
			put_page(tree_page);
I
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1108 1109
			new = &parent->rb_right;
		} else {
1110
			*tree_pagep = tree_page;
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1111 1112 1113 1114
			return tree_rmap_item;
		}
	}

H
Hugh Dickins 已提交
1115
	rmap_item->address |= UNSTABLE_FLAG;
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1116 1117 1118 1119
	rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
	rb_link_node(&rmap_item->node, parent, new);
	rb_insert_color(&rmap_item->node, &root_unstable_tree);

1120
	ksm_pages_unshared++;
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1121 1122 1123 1124 1125 1126 1127 1128 1129
	return NULL;
}

/*
 * stable_tree_append - add another rmap_item to the linked list of
 * rmap_items hanging off a given node of the stable tree, all sharing
 * the same ksm page.
 */
static void stable_tree_append(struct rmap_item *rmap_item,
H
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1130
			       struct stable_node *stable_node)
I
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1131
{
H
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1132
	rmap_item->head = stable_node;
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1133
	rmap_item->address |= STABLE_FLAG;
H
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	hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
H
Hugh Dickins 已提交
1135

H
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	if (rmap_item->hlist.next)
		ksm_pages_sharing++;
	else
		ksm_pages_shared++;
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1140 1141 1142
}

/*
H
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 * cmp_and_merge_page - first see if page can be merged into the stable tree;
 * if not, compare checksum to previous and if it's the same, see if page can
 * be inserted into the unstable tree, or merged with a page already there and
 * both transferred to the stable tree.
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1147 1148 1149 1150 1151 1152 1153
 *
 * @page: the page that we are searching identical page to.
 * @rmap_item: the reverse mapping into the virtual address of this page
 */
static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
{
	struct rmap_item *tree_rmap_item;
1154
	struct page *tree_page = NULL;
H
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1155
	struct stable_node *stable_node;
1156
	struct page *kpage;
I
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1157 1158 1159
	unsigned int checksum;
	int err;

1160
	remove_rmap_item_from_tree(rmap_item);
I
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1161 1162

	/* We first start with searching the page inside the stable tree */
1163 1164
	kpage = stable_tree_search(page);
	if (kpage) {
1165
		err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
I
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1166 1167 1168 1169 1170
		if (!err) {
			/*
			 * The page was successfully merged:
			 * add its rmap_item to the stable tree.
			 */
H
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			lock_page(kpage);
1172
			stable_tree_append(rmap_item, page_stable_node(kpage));
H
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			unlock_page(kpage);
I
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1174
		}
1175
		put_page(kpage);
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1176 1177 1178 1179
		return;
	}

	/*
H
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	 * If the hash value of the page has changed from the last time
	 * we calculated it, this page is changing frequently: therefore we
	 * don't want to insert it in the unstable tree, and we don't want
	 * to waste our time searching for something identical to it there.
I
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1184 1185 1186 1187 1188 1189 1190
	 */
	checksum = calc_checksum(page);
	if (rmap_item->oldchecksum != checksum) {
		rmap_item->oldchecksum = checksum;
		return;
	}

1191 1192
	tree_rmap_item =
		unstable_tree_search_insert(rmap_item, page, &tree_page);
I
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1193
	if (tree_rmap_item) {
1194 1195 1196
		kpage = try_to_merge_two_pages(rmap_item, page,
						tree_rmap_item, tree_page);
		put_page(tree_page);
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1197 1198 1199 1200 1201
		/*
		 * As soon as we merge this page, we want to remove the
		 * rmap_item of the page we have merged with from the unstable
		 * tree, and insert it instead as new node in the stable tree.
		 */
1202
		if (kpage) {
1203
			remove_rmap_item_from_tree(tree_rmap_item);
1204

H
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1205
			lock_page(kpage);
H
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1206 1207 1208 1209 1210
			stable_node = stable_tree_insert(kpage);
			if (stable_node) {
				stable_tree_append(tree_rmap_item, stable_node);
				stable_tree_append(rmap_item, stable_node);
			}
H
Hugh Dickins 已提交
1211
			unlock_page(kpage);
H
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1212

I
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1213 1214 1215 1216 1217 1218
			/*
			 * If we fail to insert the page into the stable tree,
			 * we will have 2 virtual addresses that are pointing
			 * to a ksm page left outside the stable tree,
			 * in which case we need to break_cow on both.
			 */
H
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1219
			if (!stable_node) {
1220 1221
				break_cow(tree_rmap_item);
				break_cow(rmap_item);
I
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1222 1223 1224 1225 1226 1227
			}
		}
	}
}

static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
H
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1228
					    struct rmap_item **rmap_list,
I
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1229 1230 1231 1232
					    unsigned long addr)
{
	struct rmap_item *rmap_item;

H
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1233 1234
	while (*rmap_list) {
		rmap_item = *rmap_list;
1235
		if ((rmap_item->address & PAGE_MASK) == addr)
I
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1236 1237 1238
			return rmap_item;
		if (rmap_item->address > addr)
			break;
H
Hugh Dickins 已提交
1239
		*rmap_list = rmap_item->rmap_list;
I
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1240 1241 1242 1243 1244 1245 1246 1247 1248
		remove_rmap_item_from_tree(rmap_item);
		free_rmap_item(rmap_item);
	}

	rmap_item = alloc_rmap_item();
	if (rmap_item) {
		/* It has already been zeroed */
		rmap_item->mm = mm_slot->mm;
		rmap_item->address = addr;
H
Hugh Dickins 已提交
1249 1250
		rmap_item->rmap_list = *rmap_list;
		*rmap_list = rmap_item;
I
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1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274
	}
	return rmap_item;
}

static struct rmap_item *scan_get_next_rmap_item(struct page **page)
{
	struct mm_struct *mm;
	struct mm_slot *slot;
	struct vm_area_struct *vma;
	struct rmap_item *rmap_item;

	if (list_empty(&ksm_mm_head.mm_list))
		return NULL;

	slot = ksm_scan.mm_slot;
	if (slot == &ksm_mm_head) {
		root_unstable_tree = RB_ROOT;

		spin_lock(&ksm_mmlist_lock);
		slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
		ksm_scan.mm_slot = slot;
		spin_unlock(&ksm_mmlist_lock);
next_mm:
		ksm_scan.address = 0;
H
Hugh Dickins 已提交
1275
		ksm_scan.rmap_list = &slot->rmap_list;
I
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1276 1277 1278 1279
	}

	mm = slot->mm;
	down_read(&mm->mmap_sem);
H
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1280 1281 1282 1283 1284 1285
	if (ksm_test_exit(mm))
		vma = NULL;
	else
		vma = find_vma(mm, ksm_scan.address);

	for (; vma; vma = vma->vm_next) {
I
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1286 1287 1288 1289 1290 1291 1292 1293
		if (!(vma->vm_flags & VM_MERGEABLE))
			continue;
		if (ksm_scan.address < vma->vm_start)
			ksm_scan.address = vma->vm_start;
		if (!vma->anon_vma)
			ksm_scan.address = vma->vm_end;

		while (ksm_scan.address < vma->vm_end) {
H
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1294 1295
			if (ksm_test_exit(mm))
				break;
I
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1296 1297 1298 1299 1300
			*page = follow_page(vma, ksm_scan.address, FOLL_GET);
			if (*page && PageAnon(*page)) {
				flush_anon_page(vma, *page, ksm_scan.address);
				flush_dcache_page(*page);
				rmap_item = get_next_rmap_item(slot,
H
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1301
					ksm_scan.rmap_list, ksm_scan.address);
I
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1302
				if (rmap_item) {
H
Hugh Dickins 已提交
1303 1304
					ksm_scan.rmap_list =
							&rmap_item->rmap_list;
I
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1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317
					ksm_scan.address += PAGE_SIZE;
				} else
					put_page(*page);
				up_read(&mm->mmap_sem);
				return rmap_item;
			}
			if (*page)
				put_page(*page);
			ksm_scan.address += PAGE_SIZE;
			cond_resched();
		}
	}

H
Hugh Dickins 已提交
1318 1319
	if (ksm_test_exit(mm)) {
		ksm_scan.address = 0;
H
Hugh Dickins 已提交
1320
		ksm_scan.rmap_list = &slot->rmap_list;
H
Hugh Dickins 已提交
1321
	}
I
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1322 1323 1324 1325
	/*
	 * Nuke all the rmap_items that are above this current rmap:
	 * because there were no VM_MERGEABLE vmas with such addresses.
	 */
H
Hugh Dickins 已提交
1326
	remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
I
Izik Eidus 已提交
1327 1328

	spin_lock(&ksm_mmlist_lock);
1329 1330 1331 1332 1333 1334 1335
	ksm_scan.mm_slot = list_entry(slot->mm_list.next,
						struct mm_slot, mm_list);
	if (ksm_scan.address == 0) {
		/*
		 * We've completed a full scan of all vmas, holding mmap_sem
		 * throughout, and found no VM_MERGEABLE: so do the same as
		 * __ksm_exit does to remove this mm from all our lists now.
H
Hugh Dickins 已提交
1336 1337 1338 1339
		 * This applies either when cleaning up after __ksm_exit
		 * (but beware: we can reach here even before __ksm_exit),
		 * or when all VM_MERGEABLE areas have been unmapped (and
		 * mmap_sem then protects against race with MADV_MERGEABLE).
1340 1341 1342
		 */
		hlist_del(&slot->link);
		list_del(&slot->mm_list);
H
Hugh Dickins 已提交
1343 1344
		spin_unlock(&ksm_mmlist_lock);

1345 1346
		free_mm_slot(slot);
		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
H
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1347 1348 1349 1350 1351
		up_read(&mm->mmap_sem);
		mmdrop(mm);
	} else {
		spin_unlock(&ksm_mmlist_lock);
		up_read(&mm->mmap_sem);
1352
	}
I
Izik Eidus 已提交
1353 1354

	/* Repeat until we've completed scanning the whole list */
1355
	slot = ksm_scan.mm_slot;
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1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382
	if (slot != &ksm_mm_head)
		goto next_mm;

	ksm_scan.seqnr++;
	return NULL;
}

/**
 * ksm_do_scan  - the ksm scanner main worker function.
 * @scan_npages - number of pages we want to scan before we return.
 */
static void ksm_do_scan(unsigned int scan_npages)
{
	struct rmap_item *rmap_item;
	struct page *page;

	while (scan_npages--) {
		cond_resched();
		rmap_item = scan_get_next_rmap_item(&page);
		if (!rmap_item)
			return;
		if (!PageKsm(page) || !in_stable_tree(rmap_item))
			cmp_and_merge_page(page, rmap_item);
		put_page(page);
	}
}

H
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1383 1384 1385 1386 1387
static int ksmd_should_run(void)
{
	return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
}

I
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1388 1389
static int ksm_scan_thread(void *nothing)
{
I
Izik Eidus 已提交
1390
	set_user_nice(current, 5);
I
Izik Eidus 已提交
1391 1392

	while (!kthread_should_stop()) {
H
Hugh Dickins 已提交
1393 1394
		mutex_lock(&ksm_thread_mutex);
		if (ksmd_should_run())
I
Izik Eidus 已提交
1395
			ksm_do_scan(ksm_thread_pages_to_scan);
H
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1396 1397 1398
		mutex_unlock(&ksm_thread_mutex);

		if (ksmd_should_run()) {
I
Izik Eidus 已提交
1399 1400 1401 1402
			schedule_timeout_interruptible(
				msecs_to_jiffies(ksm_thread_sleep_millisecs));
		} else {
			wait_event_interruptible(ksm_thread_wait,
H
Hugh Dickins 已提交
1403
				ksmd_should_run() || kthread_should_stop());
I
Izik Eidus 已提交
1404 1405 1406 1407 1408
		}
	}
	return 0;
}

H
Hugh Dickins 已提交
1409 1410 1411 1412
int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
		unsigned long end, int advice, unsigned long *vm_flags)
{
	struct mm_struct *mm = vma->vm_mm;
H
Hugh Dickins 已提交
1413
	int err;
H
Hugh Dickins 已提交
1414 1415 1416 1417 1418 1419 1420 1421 1422

	switch (advice) {
	case MADV_MERGEABLE:
		/*
		 * Be somewhat over-protective for now!
		 */
		if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
				 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
				 VM_RESERVED  | VM_HUGETLB | VM_INSERTPAGE |
H
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1423
				 VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
H
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1424 1425
			return 0;		/* just ignore the advice */

H
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1426 1427 1428 1429 1430
		if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
			err = __ksm_enter(mm);
			if (err)
				return err;
		}
H
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1431 1432 1433 1434 1435 1436 1437 1438

		*vm_flags |= VM_MERGEABLE;
		break;

	case MADV_UNMERGEABLE:
		if (!(*vm_flags & VM_MERGEABLE))
			return 0;		/* just ignore the advice */

H
Hugh Dickins 已提交
1439 1440 1441 1442 1443
		if (vma->anon_vma) {
			err = unmerge_ksm_pages(vma, start, end);
			if (err)
				return err;
		}
H
Hugh Dickins 已提交
1444 1445 1446 1447 1448 1449 1450 1451 1452 1453

		*vm_flags &= ~VM_MERGEABLE;
		break;
	}

	return 0;
}

int __ksm_enter(struct mm_struct *mm)
{
H
Hugh Dickins 已提交
1454 1455 1456 1457
	struct mm_slot *mm_slot;
	int needs_wakeup;

	mm_slot = alloc_mm_slot();
I
Izik Eidus 已提交
1458 1459 1460
	if (!mm_slot)
		return -ENOMEM;

H
Hugh Dickins 已提交
1461 1462 1463
	/* Check ksm_run too?  Would need tighter locking */
	needs_wakeup = list_empty(&ksm_mm_head.mm_list);

I
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1464 1465 1466 1467 1468 1469 1470 1471 1472 1473
	spin_lock(&ksm_mmlist_lock);
	insert_to_mm_slots_hash(mm, mm_slot);
	/*
	 * Insert just behind the scanning cursor, to let the area settle
	 * down a little; when fork is followed by immediate exec, we don't
	 * want ksmd to waste time setting up and tearing down an rmap_list.
	 */
	list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
	spin_unlock(&ksm_mmlist_lock);

H
Hugh Dickins 已提交
1474
	set_bit(MMF_VM_MERGEABLE, &mm->flags);
H
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1475
	atomic_inc(&mm->mm_count);
H
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1476 1477 1478 1479

	if (needs_wakeup)
		wake_up_interruptible(&ksm_thread_wait);

H
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1480 1481 1482
	return 0;
}

1483
void __ksm_exit(struct mm_struct *mm)
H
Hugh Dickins 已提交
1484
{
1485
	struct mm_slot *mm_slot;
H
Hugh Dickins 已提交
1486
	int easy_to_free = 0;
1487

I
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1488
	/*
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	 * This process is exiting: if it's straightforward (as is the
	 * case when ksmd was never running), free mm_slot immediately.
	 * But if it's at the cursor or has rmap_items linked to it, use
	 * mmap_sem to synchronize with any break_cows before pagetables
	 * are freed, and leave the mm_slot on the list for ksmd to free.
	 * Beware: ksm may already have noticed it exiting and freed the slot.
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	 */
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1497 1498
	spin_lock(&ksm_mmlist_lock);
	mm_slot = get_mm_slot(mm);
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	if (mm_slot && ksm_scan.mm_slot != mm_slot) {
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		if (!mm_slot->rmap_list) {
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			hlist_del(&mm_slot->link);
			list_del(&mm_slot->mm_list);
			easy_to_free = 1;
		} else {
			list_move(&mm_slot->mm_list,
				  &ksm_scan.mm_slot->mm_list);
		}
1508 1509 1510
	}
	spin_unlock(&ksm_mmlist_lock);

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	if (easy_to_free) {
		free_mm_slot(mm_slot);
		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
		mmdrop(mm);
	} else if (mm_slot) {
		down_write(&mm->mmap_sem);
		up_write(&mm->mmap_sem);
	}
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}

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struct page *ksm_does_need_to_copy(struct page *page,
			struct vm_area_struct *vma, unsigned long address)
{
	struct page *new_page;

	unlock_page(page);	/* any racers will COW it, not modify it */

	new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
	if (new_page) {
		copy_user_highpage(new_page, page, address, vma);

		SetPageDirty(new_page);
		__SetPageUptodate(new_page);
		SetPageSwapBacked(new_page);
		__set_page_locked(new_page);

		if (page_evictable(new_page, vma))
			lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
		else
			add_page_to_unevictable_list(new_page);
	}

	page_cache_release(page);
	return new_page;
}

int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
			unsigned long *vm_flags)
{
	struct stable_node *stable_node;
	struct rmap_item *rmap_item;
	struct hlist_node *hlist;
	unsigned int mapcount = page_mapcount(page);
	int referenced = 0;
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	int search_new_forks = 0;
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	VM_BUG_ON(!PageKsm(page));
	VM_BUG_ON(!PageLocked(page));

	stable_node = page_stable_node(page);
	if (!stable_node)
		return 0;
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again:
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	hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
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		struct anon_vma *anon_vma = rmap_item->anon_vma;
		struct vm_area_struct *vma;
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		spin_lock(&anon_vma->lock);
		list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
			if (rmap_item->address < vma->vm_start ||
			    rmap_item->address >= vma->vm_end)
				continue;
			/*
			 * Initially we examine only the vma which covers this
			 * rmap_item; but later, if there is still work to do,
			 * we examine covering vmas in other mms: in case they
			 * were forked from the original since ksmd passed.
			 */
			if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
				continue;

			if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
				continue;
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			referenced += page_referenced_one(page, vma,
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				rmap_item->address, &mapcount, vm_flags);
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			if (!search_new_forks || !mapcount)
				break;
		}
		spin_unlock(&anon_vma->lock);
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		if (!mapcount)
			goto out;
	}
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	if (!search_new_forks++)
		goto again;
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out:
	return referenced;
}

int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
{
	struct stable_node *stable_node;
	struct hlist_node *hlist;
	struct rmap_item *rmap_item;
	int ret = SWAP_AGAIN;
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	int search_new_forks = 0;
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	VM_BUG_ON(!PageKsm(page));
	VM_BUG_ON(!PageLocked(page));

	stable_node = page_stable_node(page);
	if (!stable_node)
		return SWAP_FAIL;
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again:
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	hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
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		struct anon_vma *anon_vma = rmap_item->anon_vma;
		struct vm_area_struct *vma;
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		spin_lock(&anon_vma->lock);
		list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
			if (rmap_item->address < vma->vm_start ||
			    rmap_item->address >= vma->vm_end)
				continue;
			/*
			 * Initially we examine only the vma which covers this
			 * rmap_item; but later, if there is still work to do,
			 * we examine covering vmas in other mms: in case they
			 * were forked from the original since ksmd passed.
			 */
			if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
				continue;

			ret = try_to_unmap_one(page, vma,
					rmap_item->address, flags);
			if (ret != SWAP_AGAIN || !page_mapped(page)) {
				spin_unlock(&anon_vma->lock);
				goto out;
			}
		}
		spin_unlock(&anon_vma->lock);
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	}
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	if (!search_new_forks++)
		goto again;
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out:
	return ret;
}

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#ifdef CONFIG_MIGRATION
int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
		  struct vm_area_struct *, unsigned long, void *), void *arg)
{
	struct stable_node *stable_node;
	struct hlist_node *hlist;
	struct rmap_item *rmap_item;
	int ret = SWAP_AGAIN;
	int search_new_forks = 0;

	VM_BUG_ON(!PageKsm(page));
	VM_BUG_ON(!PageLocked(page));

	stable_node = page_stable_node(page);
	if (!stable_node)
		return ret;
again:
	hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
		struct anon_vma *anon_vma = rmap_item->anon_vma;
		struct vm_area_struct *vma;

		spin_lock(&anon_vma->lock);
		list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
			if (rmap_item->address < vma->vm_start ||
			    rmap_item->address >= vma->vm_end)
				continue;
			/*
			 * Initially we examine only the vma which covers this
			 * rmap_item; but later, if there is still work to do,
			 * we examine covering vmas in other mms: in case they
			 * were forked from the original since ksmd passed.
			 */
			if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
				continue;

			ret = rmap_one(page, vma, rmap_item->address, arg);
			if (ret != SWAP_AGAIN) {
				spin_unlock(&anon_vma->lock);
				goto out;
			}
		}
		spin_unlock(&anon_vma->lock);
	}
	if (!search_new_forks++)
		goto again;
out:
	return ret;
}

void ksm_migrate_page(struct page *newpage, struct page *oldpage)
{
	struct stable_node *stable_node;

	VM_BUG_ON(!PageLocked(oldpage));
	VM_BUG_ON(!PageLocked(newpage));
	VM_BUG_ON(newpage->mapping != oldpage->mapping);

	stable_node = page_stable_node(newpage);
	if (stable_node) {
1707 1708
		VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
		stable_node->kpfn = page_to_pfn(newpage);
1709 1710 1711 1712
	}
}
#endif /* CONFIG_MIGRATION */

1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763
#ifdef CONFIG_MEMORY_HOTREMOVE
static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
						 unsigned long end_pfn)
{
	struct rb_node *node;

	for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
		struct stable_node *stable_node;

		stable_node = rb_entry(node, struct stable_node, node);
		if (stable_node->kpfn >= start_pfn &&
		    stable_node->kpfn < end_pfn)
			return stable_node;
	}
	return NULL;
}

static int ksm_memory_callback(struct notifier_block *self,
			       unsigned long action, void *arg)
{
	struct memory_notify *mn = arg;
	struct stable_node *stable_node;

	switch (action) {
	case MEM_GOING_OFFLINE:
		/*
		 * Keep it very simple for now: just lock out ksmd and
		 * MADV_UNMERGEABLE while any memory is going offline.
		 */
		mutex_lock(&ksm_thread_mutex);
		break;

	case MEM_OFFLINE:
		/*
		 * Most of the work is done by page migration; but there might
		 * be a few stable_nodes left over, still pointing to struct
		 * pages which have been offlined: prune those from the tree.
		 */
		while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
					mn->start_pfn + mn->nr_pages)) != NULL)
			remove_node_from_stable_tree(stable_node);
		/* fallthrough */

	case MEM_CANCEL_OFFLINE:
		mutex_unlock(&ksm_thread_mutex);
		break;
	}
	return NOTIFY_OK;
}
#endif /* CONFIG_MEMORY_HOTREMOVE */

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#ifdef CONFIG_SYSFS
/*
 * This all compiles without CONFIG_SYSFS, but is a waste of space.
 */

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#define KSM_ATTR_RO(_name) \
	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
#define KSM_ATTR(_name) \
	static struct kobj_attribute _name##_attr = \
		__ATTR(_name, 0644, _name##_show, _name##_store)

static ssize_t sleep_millisecs_show(struct kobject *kobj,
				    struct kobj_attribute *attr, char *buf)
{
	return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
}

static ssize_t sleep_millisecs_store(struct kobject *kobj,
				     struct kobj_attribute *attr,
				     const char *buf, size_t count)
{
	unsigned long msecs;
	int err;

	err = strict_strtoul(buf, 10, &msecs);
	if (err || msecs > UINT_MAX)
		return -EINVAL;

	ksm_thread_sleep_millisecs = msecs;

	return count;
}
KSM_ATTR(sleep_millisecs);

static ssize_t pages_to_scan_show(struct kobject *kobj,
				  struct kobj_attribute *attr, char *buf)
{
	return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
}

static ssize_t pages_to_scan_store(struct kobject *kobj,
				   struct kobj_attribute *attr,
				   const char *buf, size_t count)
{
	int err;
	unsigned long nr_pages;

	err = strict_strtoul(buf, 10, &nr_pages);
	if (err || nr_pages > UINT_MAX)
		return -EINVAL;

	ksm_thread_pages_to_scan = nr_pages;

	return count;
}
KSM_ATTR(pages_to_scan);

static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
			char *buf)
{
	return sprintf(buf, "%u\n", ksm_run);
}

static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
			 const char *buf, size_t count)
{
	int err;
	unsigned long flags;

	err = strict_strtoul(buf, 10, &flags);
	if (err || flags > UINT_MAX)
		return -EINVAL;
	if (flags > KSM_RUN_UNMERGE)
		return -EINVAL;

	/*
	 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
	 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1842 1843
	 * breaking COW to free the pages_shared (but leaves mm_slots
	 * on the list for when ksmd may be set running again).
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1844 1845 1846 1847 1848
	 */

	mutex_lock(&ksm_thread_mutex);
	if (ksm_run != flags) {
		ksm_run = flags;
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		if (flags & KSM_RUN_UNMERGE) {
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			current->flags |= PF_OOM_ORIGIN;
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1851
			err = unmerge_and_remove_all_rmap_items();
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			current->flags &= ~PF_OOM_ORIGIN;
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			if (err) {
				ksm_run = KSM_RUN_STOP;
				count = err;
			}
		}
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	}
	mutex_unlock(&ksm_thread_mutex);

	if (flags & KSM_RUN_MERGE)
		wake_up_interruptible(&ksm_thread_wait);

	return count;
}
KSM_ATTR(run);

1868 1869 1870 1871 1872 1873 1874 1875 1876 1877
static ssize_t pages_shared_show(struct kobject *kobj,
				 struct kobj_attribute *attr, char *buf)
{
	return sprintf(buf, "%lu\n", ksm_pages_shared);
}
KSM_ATTR_RO(pages_shared);

static ssize_t pages_sharing_show(struct kobject *kobj,
				  struct kobj_attribute *attr, char *buf)
{
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	return sprintf(buf, "%lu\n", ksm_pages_sharing);
1879 1880 1881
}
KSM_ATTR_RO(pages_sharing);

1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912
static ssize_t pages_unshared_show(struct kobject *kobj,
				   struct kobj_attribute *attr, char *buf)
{
	return sprintf(buf, "%lu\n", ksm_pages_unshared);
}
KSM_ATTR_RO(pages_unshared);

static ssize_t pages_volatile_show(struct kobject *kobj,
				   struct kobj_attribute *attr, char *buf)
{
	long ksm_pages_volatile;

	ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
				- ksm_pages_sharing - ksm_pages_unshared;
	/*
	 * It was not worth any locking to calculate that statistic,
	 * but it might therefore sometimes be negative: conceal that.
	 */
	if (ksm_pages_volatile < 0)
		ksm_pages_volatile = 0;
	return sprintf(buf, "%ld\n", ksm_pages_volatile);
}
KSM_ATTR_RO(pages_volatile);

static ssize_t full_scans_show(struct kobject *kobj,
			       struct kobj_attribute *attr, char *buf)
{
	return sprintf(buf, "%lu\n", ksm_scan.seqnr);
}
KSM_ATTR_RO(full_scans);

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static struct attribute *ksm_attrs[] = {
	&sleep_millisecs_attr.attr,
	&pages_to_scan_attr.attr,
	&run_attr.attr,
1917 1918
	&pages_shared_attr.attr,
	&pages_sharing_attr.attr,
1919 1920 1921
	&pages_unshared_attr.attr,
	&pages_volatile_attr.attr,
	&full_scans_attr.attr,
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	NULL,
};

static struct attribute_group ksm_attr_group = {
	.attrs = ksm_attrs,
	.name = "ksm",
};
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#endif /* CONFIG_SYSFS */
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static int __init ksm_init(void)
{
	struct task_struct *ksm_thread;
	int err;

	err = ksm_slab_init();
	if (err)
		goto out;

	err = mm_slots_hash_init();
	if (err)
		goto out_free1;

	ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
	if (IS_ERR(ksm_thread)) {
		printk(KERN_ERR "ksm: creating kthread failed\n");
		err = PTR_ERR(ksm_thread);
		goto out_free2;
	}

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#ifdef CONFIG_SYSFS
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	err = sysfs_create_group(mm_kobj, &ksm_attr_group);
	if (err) {
		printk(KERN_ERR "ksm: register sysfs failed\n");
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		kthread_stop(ksm_thread);
		goto out_free2;
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1957
	}
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#else
	ksm_run = KSM_RUN_MERGE;	/* no way for user to start it */

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#endif /* CONFIG_SYSFS */
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1962

1963 1964 1965 1966 1967 1968 1969
#ifdef CONFIG_MEMORY_HOTREMOVE
	/*
	 * Choose a high priority since the callback takes ksm_thread_mutex:
	 * later callbacks could only be taking locks which nest within that.
	 */
	hotplug_memory_notifier(ksm_memory_callback, 100);
#endif
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	return 0;

out_free2:
	mm_slots_hash_free();
out_free1:
	ksm_slab_free();
out:
	return err;
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}
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module_init(ksm_init)