ksm.c 50.3 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>
#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
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 * @page: pointer to struct page of the ksm page
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 * @node: rb node of this ksm page in the stable tree
 * @hlist: hlist head of rmap_items using this ksm page
 */
struct stable_node {
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	struct page *page;
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	struct rb_node node;
	struct hlist_head hlist;
};

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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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/* Limit on the number of unswappable pages used */
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static unsigned long ksm_max_kernel_pages;
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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;

	page = stable_node->page;
	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
Izik Eidus 已提交
538 539 540 541 542 543
/*
 * 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
544 545
	if (rmap_item->address & STABLE_FLAG) {
		struct stable_node *stable_node;
H
Hugh Dickins 已提交
546
		struct page *page;
I
Izik Eidus 已提交
547

H
Hugh Dickins 已提交
548
		stable_node = rmap_item->head;
H
Hugh Dickins 已提交
549 550 551
		page = get_ksm_page(stable_node);
		if (!page)
			goto out;
H
Hugh Dickins 已提交
552

H
Hugh Dickins 已提交
553
		lock_page(page);
H
Hugh Dickins 已提交
554
		hlist_del(&rmap_item->hlist);
H
Hugh Dickins 已提交
555 556
		unlock_page(page);
		put_page(page);
557

H
Hugh Dickins 已提交
558 559 560
		if (stable_node->hlist.first)
			ksm_pages_sharing--;
		else
H
Hugh Dickins 已提交
561
			ksm_pages_shared--;
I
Izik Eidus 已提交
562

H
Hugh Dickins 已提交
563
		drop_anon_vma(rmap_item);
564
		rmap_item->address &= PAGE_MASK;
I
Izik Eidus 已提交
565

H
Hugh Dickins 已提交
566
	} else if (rmap_item->address & UNSTABLE_FLAG) {
I
Izik Eidus 已提交
567 568
		unsigned char age;
		/*
H
Hugh Dickins 已提交
569
		 * Usually ksmd can and must skip the rb_erase, because
I
Izik Eidus 已提交
570
		 * root_unstable_tree was already reset to RB_ROOT.
H
Hugh Dickins 已提交
571 572 573
		 * 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
574 575
		 */
		age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
576
		BUG_ON(age > 1);
I
Izik Eidus 已提交
577 578
		if (!age)
			rb_erase(&rmap_item->node, &root_unstable_tree);
579

580
		ksm_pages_unshared--;
581
		rmap_item->address &= PAGE_MASK;
I
Izik Eidus 已提交
582
	}
H
Hugh Dickins 已提交
583
out:
I
Izik Eidus 已提交
584 585 586 587
	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
588
				       struct rmap_item **rmap_list)
I
Izik Eidus 已提交
589
{
H
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590 591 592
	while (*rmap_list) {
		struct rmap_item *rmap_item = *rmap_list;
		*rmap_list = rmap_item->rmap_list;
I
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593 594 595 596 597 598 599 600 601 602 603 604
		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
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605 606 607 608 609
 *
 * 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
610
 */
H
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611 612
static int unmerge_ksm_pages(struct vm_area_struct *vma,
			     unsigned long start, unsigned long end)
I
Izik Eidus 已提交
613 614
{
	unsigned long addr;
H
Hugh Dickins 已提交
615
	int err = 0;
I
Izik Eidus 已提交
616

H
Hugh Dickins 已提交
617
	for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
H
Hugh Dickins 已提交
618 619
		if (ksm_test_exit(vma->vm_mm))
			break;
H
Hugh Dickins 已提交
620 621 622 623 624 625
		if (signal_pending(current))
			err = -ERESTARTSYS;
		else
			err = break_ksm(vma, addr);
	}
	return err;
I
Izik Eidus 已提交
626 627
}

H
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628 629 630 631
#ifdef CONFIG_SYSFS
/*
 * Only called through the sysfs control interface:
 */
H
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632
static int unmerge_and_remove_all_rmap_items(void)
I
Izik Eidus 已提交
633 634 635 636
{
	struct mm_slot *mm_slot;
	struct mm_struct *mm;
	struct vm_area_struct *vma;
H
Hugh Dickins 已提交
637 638 639
	int err = 0;

	spin_lock(&ksm_mmlist_lock);
H
Hugh Dickins 已提交
640
	ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
H
Hugh Dickins 已提交
641 642
						struct mm_slot, mm_list);
	spin_unlock(&ksm_mmlist_lock);
I
Izik Eidus 已提交
643

H
Hugh Dickins 已提交
644 645
	for (mm_slot = ksm_scan.mm_slot;
			mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
I
Izik Eidus 已提交
646 647 648
		mm = mm_slot->mm;
		down_read(&mm->mmap_sem);
		for (vma = mm->mmap; vma; vma = vma->vm_next) {
H
Hugh Dickins 已提交
649 650
			if (ksm_test_exit(mm))
				break;
I
Izik Eidus 已提交
651 652
			if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
				continue;
H
Hugh Dickins 已提交
653 654
			err = unmerge_ksm_pages(vma,
						vma->vm_start, vma->vm_end);
H
Hugh Dickins 已提交
655 656
			if (err)
				goto error;
I
Izik Eidus 已提交
657
		}
H
Hugh Dickins 已提交
658

H
Hugh Dickins 已提交
659
		remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
H
Hugh Dickins 已提交
660 661

		spin_lock(&ksm_mmlist_lock);
H
Hugh Dickins 已提交
662
		ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
H
Hugh Dickins 已提交
663
						struct mm_slot, mm_list);
H
Hugh Dickins 已提交
664 665 666 667 668 669 670 671 672 673 674 675 676
		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
677 678
	}

H
Hugh Dickins 已提交
679
	ksm_scan.seqnr = 0;
H
Hugh Dickins 已提交
680 681 682 683
	return 0;

error:
	up_read(&mm->mmap_sem);
I
Izik Eidus 已提交
684
	spin_lock(&ksm_mmlist_lock);
H
Hugh Dickins 已提交
685
	ksm_scan.mm_slot = &ksm_mm_head;
I
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686
	spin_unlock(&ksm_mmlist_lock);
H
Hugh Dickins 已提交
687
	return err;
I
Izik Eidus 已提交
688
}
H
Hugh Dickins 已提交
689
#endif /* CONFIG_SYSFS */
I
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690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754

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
		 */
755
		if (page_mapcount(page) + 1 + swapped != page_count(page)) {
I
Izik Eidus 已提交
756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772
			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
773 774 775
 * @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
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776 777 778 779
 * @orig_pte: the original value of the pte
 *
 * Returns 0 on success, -EFAULT on failure.
 */
780 781
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
782 783 784 785 786 787 788 789 790 791
{
	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;

792
	addr = page_address_in_vma(page, vma);
I
Izik Eidus 已提交
793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813
	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;
	}

814
	get_page(kpage);
H
Hugh Dickins 已提交
815
	page_add_anon_rmap(kpage, vma, addr);
I
Izik Eidus 已提交
816 817 818

	flush_cache_page(vma, addr, pte_pfn(*ptep));
	ptep_clear_flush(vma, addr, ptep);
819
	set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
I
Izik Eidus 已提交
820

821 822
	page_remove_rmap(page);
	put_page(page);
I
Izik Eidus 已提交
823 824 825 826 827 828 829 830 831

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

/*
 * try_to_merge_one_page - take two pages and merge them into one
832 833
 * @vma: the vma that holds the pte pointing to page
 * @page: the PageAnon page that we want to replace with kpage
834 835
 * @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
836 837 838 839
 *
 * This function returns 0 if the pages were merged, -EFAULT otherwise.
 */
static int try_to_merge_one_page(struct vm_area_struct *vma,
840
				 struct page *page, struct page *kpage)
I
Izik Eidus 已提交
841 842 843 844
{
	pte_t orig_pte = __pte(0);
	int err = -EFAULT;

H
Hugh Dickins 已提交
845 846 847
	if (page == kpage)			/* ksm page forked */
		return 0;

I
Izik Eidus 已提交
848 849
	if (!(vma->vm_flags & VM_MERGEABLE))
		goto out;
850
	if (!PageAnon(page))
I
Izik Eidus 已提交
851 852 853 854 855 856 857 858 859
		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.
	 */
860
	if (!trylock_page(page))
861
		goto out;
I
Izik Eidus 已提交
862 863 864 865 866 867
	/*
	 * 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.
	 */
868 869 870 871 872 873 874 875 876 877 878 879 880
	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
881

882
	if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
H
Hugh Dickins 已提交
883
		munlock_vma_page(page);
H
Hugh Dickins 已提交
884 885 886 887 888 889 890
		if (!PageMlocked(kpage)) {
			unlock_page(page);
			lock_page(kpage);
			mlock_vma_page(kpage);
			page = kpage;		/* for final unlock */
		}
	}
H
Hugh Dickins 已提交
891

892
	unlock_page(page);
I
Izik Eidus 已提交
893 894 895 896
out:
	return err;
}

H
Hugh Dickins 已提交
897 898 899
/*
 * 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.
900 901
 *
 * This function returns 0 if the pages were merged, -EFAULT otherwise.
H
Hugh Dickins 已提交
902
 */
903 904
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
905
{
906
	struct mm_struct *mm = rmap_item->mm;
H
Hugh Dickins 已提交
907 908 909
	struct vm_area_struct *vma;
	int err = -EFAULT;

910 911
	down_read(&mm->mmap_sem);
	if (ksm_test_exit(mm))
H
Hugh Dickins 已提交
912
		goto out;
913 914
	vma = find_vma(mm, rmap_item->address);
	if (!vma || vma->vm_start > rmap_item->address)
H
Hugh Dickins 已提交
915 916
		goto out;

917
	err = try_to_merge_one_page(vma, page, kpage);
H
Hugh Dickins 已提交
918 919 920 921 922
	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
923
out:
924
	up_read(&mm->mmap_sem);
H
Hugh Dickins 已提交
925 926 927
	return err;
}

I
Izik Eidus 已提交
928 929 930 931
/*
 * try_to_merge_two_pages - take two identical pages and prepare them
 * to be merged into one page.
 *
932 933
 * This function returns the kpage if we successfully merged two identical
 * pages into one ksm page, NULL otherwise.
I
Izik Eidus 已提交
934
 *
935
 * Note that this function upgrades page to ksm page: if one of the pages
I
Izik Eidus 已提交
936 937
 * is already a ksm page, try_to_merge_with_ksm_page should be used.
 */
938 939 940 941
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
942
{
943
	int err;
I
Izik Eidus 已提交
944 945 946 947 948 949

	/*
	 * The number of nodes in the stable tree
	 * is the number of kernel pages that we hold.
	 */
	if (ksm_max_kernel_pages &&
950
	    ksm_max_kernel_pages <= ksm_pages_shared)
951
		return NULL;
I
Izik Eidus 已提交
952

953
	err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
I
Izik Eidus 已提交
954
	if (!err) {
955
		err = try_to_merge_with_ksm_page(tree_rmap_item,
956
							tree_page, page);
I
Izik Eidus 已提交
957
		/*
H
Hugh Dickins 已提交
958 959
		 * If that fails, we have a ksm page with only one pte
		 * pointing to it: so break it.
I
Izik Eidus 已提交
960
		 */
H
Hugh Dickins 已提交
961
		if (err)
962
			break_cow(rmap_item);
I
Izik Eidus 已提交
963
	}
964
	return err ? NULL : page;
I
Izik Eidus 已提交
965 966 967
}

/*
968
 * stable_tree_search - search for page inside the stable tree
I
Izik Eidus 已提交
969 970 971 972
 *
 * 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
973
 * This function returns the stable tree node of identical content if found,
I
Izik Eidus 已提交
974 975
 * NULL otherwise.
 */
976
static struct stable_node *stable_tree_search(struct page *page)
I
Izik Eidus 已提交
977 978
{
	struct rb_node *node = root_stable_tree.rb_node;
H
Hugh Dickins 已提交
979
	struct stable_node *stable_node;
I
Izik Eidus 已提交
980

981 982 983 984 985 986
	stable_node = page_stable_node(page);
	if (stable_node) {			/* ksm page forked */
		get_page(page);
		return stable_node;
	}

I
Izik Eidus 已提交
987
	while (node) {
H
Hugh Dickins 已提交
988
		struct page *tree_page;
I
Izik Eidus 已提交
989 990
		int ret;

991
		cond_resched();
H
Hugh Dickins 已提交
992
		stable_node = rb_entry(node, struct stable_node, node);
H
Hugh Dickins 已提交
993 994 995
		tree_page = get_ksm_page(stable_node);
		if (!tree_page)
			return NULL;
I
Izik Eidus 已提交
996

H
Hugh Dickins 已提交
997
		ret = memcmp_pages(page, tree_page);
I
Izik Eidus 已提交
998

H
Hugh Dickins 已提交
999 1000
		if (ret < 0) {
			put_page(tree_page);
I
Izik Eidus 已提交
1001
			node = node->rb_left;
H
Hugh Dickins 已提交
1002 1003
		} else if (ret > 0) {
			put_page(tree_page);
I
Izik Eidus 已提交
1004
			node = node->rb_right;
H
Hugh Dickins 已提交
1005
		} else
H
Hugh Dickins 已提交
1006
			return stable_node;
I
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	}

	return NULL;
}

/*
 * stable_tree_insert - insert rmap_item pointing to new ksm page
 * into the stable tree.
 *
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 * This function returns the stable tree node just allocated on success,
 * NULL otherwise.
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1018
 */
H
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1019
static struct stable_node *stable_tree_insert(struct page *kpage)
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1020 1021 1022
{
	struct rb_node **new = &root_stable_tree.rb_node;
	struct rb_node *parent = NULL;
H
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	struct stable_node *stable_node;
I
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1024 1025

	while (*new) {
H
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1026
		struct page *tree_page;
I
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1027 1028
		int ret;

1029
		cond_resched();
H
Hugh Dickins 已提交
1030
		stable_node = rb_entry(*new, struct stable_node, node);
H
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1031 1032 1033
		tree_page = get_ksm_page(stable_node);
		if (!tree_page)
			return NULL;
I
Izik Eidus 已提交
1034

H
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1035 1036
		ret = memcmp_pages(kpage, tree_page);
		put_page(tree_page);
I
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1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052

		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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1053 1054 1055
	stable_node = alloc_stable_node();
	if (!stable_node)
		return NULL;
I
Izik Eidus 已提交
1056

H
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1057 1058 1059 1060 1061
	rb_link_node(&stable_node->node, parent, new);
	rb_insert_color(&stable_node->node, &root_stable_tree);

	INIT_HLIST_HEAD(&stable_node->hlist);

1062 1063 1064
	stable_node->page = kpage;
	set_page_stable_node(kpage, stable_node);

H
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1065
	return stable_node;
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1066 1067 1068
}

/*
1069 1070
 * unstable_tree_search_insert - search for identical page,
 * else insert rmap_item into the unstable tree.
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1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081
 *
 * 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.
 */
1082 1083 1084 1085 1086
static
struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
					      struct page *page,
					      struct page **tree_pagep)

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1087 1088 1089 1090 1091 1092
{
	struct rb_node **new = &root_unstable_tree.rb_node;
	struct rb_node *parent = NULL;

	while (*new) {
		struct rmap_item *tree_rmap_item;
1093
		struct page *tree_page;
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1094 1095
		int ret;

H
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1096
		cond_resched();
I
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1097
		tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1098 1099
		tree_page = get_mergeable_page(tree_rmap_item);
		if (!tree_page)
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1100 1101 1102
			return NULL;

		/*
1103
		 * Don't substitute a ksm page for a forked page.
I
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1104
		 */
1105 1106
		if (page == tree_page) {
			put_page(tree_page);
I
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1107 1108 1109
			return NULL;
		}

1110
		ret = memcmp_pages(page, tree_page);
I
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1111 1112 1113

		parent = *new;
		if (ret < 0) {
1114
			put_page(tree_page);
I
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1115 1116
			new = &parent->rb_left;
		} else if (ret > 0) {
1117
			put_page(tree_page);
I
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1118 1119
			new = &parent->rb_right;
		} else {
1120
			*tree_pagep = tree_page;
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1121 1122 1123 1124
			return tree_rmap_item;
		}
	}

H
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1125
	rmap_item->address |= UNSTABLE_FLAG;
I
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1126 1127 1128 1129
	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);

1130
	ksm_pages_unshared++;
I
Izik Eidus 已提交
1131 1132 1133 1134 1135 1136 1137 1138 1139
	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
Hugh Dickins 已提交
1140
			       struct stable_node *stable_node)
I
Izik Eidus 已提交
1141
{
H
Hugh Dickins 已提交
1142
	rmap_item->head = stable_node;
I
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1143
	rmap_item->address |= STABLE_FLAG;
H
Hugh Dickins 已提交
1144
	hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
H
Hugh Dickins 已提交
1145

H
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1146 1147 1148 1149
	if (rmap_item->hlist.next)
		ksm_pages_sharing++;
	else
		ksm_pages_shared++;
I
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1150 1151 1152
}

/*
H
Hugh Dickins 已提交
1153 1154 1155 1156
 * 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.
I
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1157 1158 1159 1160 1161 1162 1163
 *
 * @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;
1164
	struct page *tree_page = NULL;
H
Hugh Dickins 已提交
1165
	struct stable_node *stable_node;
1166
	struct page *kpage;
I
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1167 1168 1169
	unsigned int checksum;
	int err;

1170
	remove_rmap_item_from_tree(rmap_item);
I
Izik Eidus 已提交
1171 1172

	/* We first start with searching the page inside the stable tree */
1173
	stable_node = stable_tree_search(page);
H
Hugh Dickins 已提交
1174
	if (stable_node) {
1175 1176
		kpage = stable_node->page;
		err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
I
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1177 1178 1179 1180 1181
		if (!err) {
			/*
			 * The page was successfully merged:
			 * add its rmap_item to the stable tree.
			 */
H
Hugh Dickins 已提交
1182
			lock_page(kpage);
H
Hugh Dickins 已提交
1183
			stable_tree_append(rmap_item, stable_node);
H
Hugh Dickins 已提交
1184
			unlock_page(kpage);
I
Izik Eidus 已提交
1185
		}
1186
		put_page(kpage);
I
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1187 1188 1189 1190
		return;
	}

	/*
H
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1191 1192 1193 1194
	 * 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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1195 1196 1197 1198 1199 1200 1201
	 */
	checksum = calc_checksum(page);
	if (rmap_item->oldchecksum != checksum) {
		rmap_item->oldchecksum = checksum;
		return;
	}

1202 1203
	tree_rmap_item =
		unstable_tree_search_insert(rmap_item, page, &tree_page);
I
Izik Eidus 已提交
1204
	if (tree_rmap_item) {
1205 1206 1207
		kpage = try_to_merge_two_pages(rmap_item, page,
						tree_rmap_item, tree_page);
		put_page(tree_page);
I
Izik Eidus 已提交
1208 1209 1210 1211 1212
		/*
		 * 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.
		 */
1213
		if (kpage) {
1214
			remove_rmap_item_from_tree(tree_rmap_item);
1215

H
Hugh Dickins 已提交
1216
			lock_page(kpage);
H
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1217 1218 1219 1220 1221
			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
1222
			unlock_page(kpage);
H
Hugh Dickins 已提交
1223

I
Izik Eidus 已提交
1224 1225 1226 1227 1228 1229
			/*
			 * 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
Hugh Dickins 已提交
1230
			if (!stable_node) {
1231 1232
				break_cow(tree_rmap_item);
				break_cow(rmap_item);
I
Izik Eidus 已提交
1233 1234 1235 1236 1237 1238
			}
		}
	}
}

static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
H
Hugh Dickins 已提交
1239
					    struct rmap_item **rmap_list,
I
Izik Eidus 已提交
1240 1241 1242 1243
					    unsigned long addr)
{
	struct rmap_item *rmap_item;

H
Hugh Dickins 已提交
1244 1245
	while (*rmap_list) {
		rmap_item = *rmap_list;
1246
		if ((rmap_item->address & PAGE_MASK) == addr)
I
Izik Eidus 已提交
1247 1248 1249
			return rmap_item;
		if (rmap_item->address > addr)
			break;
H
Hugh Dickins 已提交
1250
		*rmap_list = rmap_item->rmap_list;
I
Izik Eidus 已提交
1251 1252 1253 1254 1255 1256 1257 1258 1259
		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
1260 1261
		rmap_item->rmap_list = *rmap_list;
		*rmap_list = rmap_item;
I
Izik Eidus 已提交
1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285
	}
	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
1286
		ksm_scan.rmap_list = &slot->rmap_list;
I
Izik Eidus 已提交
1287 1288 1289 1290
	}

	mm = slot->mm;
	down_read(&mm->mmap_sem);
H
Hugh Dickins 已提交
1291 1292 1293 1294 1295 1296
	if (ksm_test_exit(mm))
		vma = NULL;
	else
		vma = find_vma(mm, ksm_scan.address);

	for (; vma; vma = vma->vm_next) {
I
Izik Eidus 已提交
1297 1298 1299 1300 1301 1302 1303 1304
		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
Hugh Dickins 已提交
1305 1306
			if (ksm_test_exit(mm))
				break;
I
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1307 1308 1309 1310 1311
			*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
Hugh Dickins 已提交
1312
					ksm_scan.rmap_list, ksm_scan.address);
I
Izik Eidus 已提交
1313
				if (rmap_item) {
H
Hugh Dickins 已提交
1314 1315
					ksm_scan.rmap_list =
							&rmap_item->rmap_list;
I
Izik Eidus 已提交
1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328
					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
1329 1330
	if (ksm_test_exit(mm)) {
		ksm_scan.address = 0;
H
Hugh Dickins 已提交
1331
		ksm_scan.rmap_list = &slot->rmap_list;
H
Hugh Dickins 已提交
1332
	}
I
Izik Eidus 已提交
1333 1334 1335 1336
	/*
	 * 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
1337
	remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
I
Izik Eidus 已提交
1338 1339

	spin_lock(&ksm_mmlist_lock);
1340 1341 1342 1343 1344 1345 1346
	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
1347 1348 1349 1350
		 * 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).
1351 1352 1353
		 */
		hlist_del(&slot->link);
		list_del(&slot->mm_list);
H
Hugh Dickins 已提交
1354 1355
		spin_unlock(&ksm_mmlist_lock);

1356 1357
		free_mm_slot(slot);
		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
H
Hugh Dickins 已提交
1358 1359 1360 1361 1362
		up_read(&mm->mmap_sem);
		mmdrop(mm);
	} else {
		spin_unlock(&ksm_mmlist_lock);
		up_read(&mm->mmap_sem);
1363
	}
I
Izik Eidus 已提交
1364 1365

	/* Repeat until we've completed scanning the whole list */
1366
	slot = ksm_scan.mm_slot;
I
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1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393
	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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1394 1395 1396 1397 1398
static int ksmd_should_run(void)
{
	return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
}

I
Izik Eidus 已提交
1399 1400
static int ksm_scan_thread(void *nothing)
{
I
Izik Eidus 已提交
1401
	set_user_nice(current, 5);
I
Izik Eidus 已提交
1402 1403

	while (!kthread_should_stop()) {
H
Hugh Dickins 已提交
1404 1405
		mutex_lock(&ksm_thread_mutex);
		if (ksmd_should_run())
I
Izik Eidus 已提交
1406
			ksm_do_scan(ksm_thread_pages_to_scan);
H
Hugh Dickins 已提交
1407 1408 1409
		mutex_unlock(&ksm_thread_mutex);

		if (ksmd_should_run()) {
I
Izik Eidus 已提交
1410 1411 1412 1413
			schedule_timeout_interruptible(
				msecs_to_jiffies(ksm_thread_sleep_millisecs));
		} else {
			wait_event_interruptible(ksm_thread_wait,
H
Hugh Dickins 已提交
1414
				ksmd_should_run() || kthread_should_stop());
I
Izik Eidus 已提交
1415 1416 1417 1418 1419
		}
	}
	return 0;
}

H
Hugh Dickins 已提交
1420 1421 1422 1423
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
1424
	int err;
H
Hugh Dickins 已提交
1425 1426 1427 1428 1429 1430 1431 1432 1433

	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
Hugh Dickins 已提交
1434
				 VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
H
Hugh Dickins 已提交
1435 1436
			return 0;		/* just ignore the advice */

H
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1437 1438 1439 1440 1441
		if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
			err = __ksm_enter(mm);
			if (err)
				return err;
		}
H
Hugh Dickins 已提交
1442 1443 1444 1445 1446 1447 1448 1449

		*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
1450 1451 1452 1453 1454
		if (vma->anon_vma) {
			err = unmerge_ksm_pages(vma, start, end);
			if (err)
				return err;
		}
H
Hugh Dickins 已提交
1455 1456 1457 1458 1459 1460 1461 1462 1463 1464

		*vm_flags &= ~VM_MERGEABLE;
		break;
	}

	return 0;
}

int __ksm_enter(struct mm_struct *mm)
{
H
Hugh Dickins 已提交
1465 1466 1467 1468
	struct mm_slot *mm_slot;
	int needs_wakeup;

	mm_slot = alloc_mm_slot();
I
Izik Eidus 已提交
1469 1470 1471
	if (!mm_slot)
		return -ENOMEM;

H
Hugh Dickins 已提交
1472 1473 1474
	/* Check ksm_run too?  Would need tighter locking */
	needs_wakeup = list_empty(&ksm_mm_head.mm_list);

I
Izik Eidus 已提交
1475 1476 1477 1478 1479 1480 1481 1482 1483 1484
	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
1485
	set_bit(MMF_VM_MERGEABLE, &mm->flags);
H
Hugh Dickins 已提交
1486
	atomic_inc(&mm->mm_count);
H
Hugh Dickins 已提交
1487 1488 1489 1490

	if (needs_wakeup)
		wake_up_interruptible(&ksm_thread_wait);

H
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	return 0;
}

1494
void __ksm_exit(struct mm_struct *mm)
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{
1496
	struct mm_slot *mm_slot;
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	int easy_to_free = 0;
1498

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	/*
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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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1508 1509
	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);
		}
1519 1520 1521
	}
	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_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,
1737
	 * breaking COW to free the unswappable pages_shared (but leaves
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1738 1739 1740 1741 1742 1743
	 * mm_slots on the list for when ksmd may be set running again).
	 */

	mutex_lock(&ksm_thread_mutex);
	if (ksm_run != flags) {
		ksm_run = flags;
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		if (flags & KSM_RUN_UNMERGE) {
H
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			current->flags |= PF_OOM_ORIGIN;
H
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1746
			err = unmerge_and_remove_all_rmap_items();
H
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1747
			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);

static ssize_t max_kernel_pages_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)
		return -EINVAL;

	ksm_max_kernel_pages = nr_pages;

	return count;
}

static ssize_t max_kernel_pages_show(struct kobject *kobj,
				     struct kobj_attribute *attr, char *buf)
{
	return sprintf(buf, "%lu\n", ksm_max_kernel_pages);
}
KSM_ATTR(max_kernel_pages);

1786 1787 1788 1789 1790 1791 1792 1793 1794 1795
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);
1797 1798 1799
}
KSM_ATTR_RO(pages_sharing);

1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830
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,
	&max_kernel_pages_attr.attr,
1836 1837
	&pages_shared_attr.attr,
	&pages_sharing_attr.attr,
1838 1839 1840
	&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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1849 1850 1851 1852 1853 1854

static int __init ksm_init(void)
{
	struct task_struct *ksm_thread;
	int err;

H
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1855
	ksm_max_kernel_pages = totalram_pages / 4;
1856

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1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871
	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
I
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1873 1874 1875
	err = sysfs_create_group(mm_kobj, &ksm_attr_group);
	if (err) {
		printk(KERN_ERR "ksm: register sysfs failed\n");
H
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1876 1877
		kthread_stop(ksm_thread);
		goto out_free2;
I
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1878
	}
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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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	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)