ksm.c 54.7 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 <linux/hash.h>
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#include <linux/freezer.h>
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#include <linux/oom.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;

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#define MM_SLOTS_HASH_SHIFT 10
#define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT)
static struct hlist_head mm_slots_hash[MM_SLOTS_HASH_HEADS];
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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 struct mm_slot *get_mm_slot(struct mm_struct *mm)
{
	struct mm_slot *mm_slot;
	struct hlist_head *bucket;
	struct hlist_node *node;

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	bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
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	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;

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	bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
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	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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/*
 * 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);
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		if (IS_ERR_OR_NULL(page))
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			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 struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
		unsigned long addr)
{
	struct vm_area_struct *vma;
	if (ksm_test_exit(mm))
		return NULL;
	vma = find_vma(mm, addr);
	if (!vma || vma->vm_start > addr)
		return NULL;
	if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
		return NULL;
	return vma;
}

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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.
	 */
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	put_anon_vma(rmap_item->anon_vma);
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	down_read(&mm->mmap_sem);
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	vma = find_mergeable_vma(mm, addr);
	if (vma)
		break_ksm(vma, addr);
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	up_read(&mm->mmap_sem);
}

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static struct page *page_trans_compound_anon(struct page *page)
{
	if (PageTransCompound(page)) {
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		struct page *head = compound_trans_head(page);
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		/*
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		 * head may actually be splitted and freed from under
		 * us but it's ok here.
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		 */
		if (PageAnon(head))
			return head;
	}
	return NULL;
}

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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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	vma = find_mergeable_vma(mm, addr);
	if (!vma)
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		goto out;

	page = follow_page(vma, addr, FOLL_GET);
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	if (IS_ERR_OR_NULL(page))
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		goto out;
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	if (PageAnon(page) || page_trans_compound_anon(page)) {
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		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--;
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		put_anon_vma(rmap_item->anon_vma);
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		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
Izik Eidus 已提交
523 524 525 526 527 528
/*
 * 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
529 530
	if (rmap_item->address & STABLE_FLAG) {
		struct stable_node *stable_node;
H
Hugh Dickins 已提交
531
		struct page *page;
I
Izik Eidus 已提交
532

H
Hugh Dickins 已提交
533
		stable_node = rmap_item->head;
H
Hugh Dickins 已提交
534 535 536
		page = get_ksm_page(stable_node);
		if (!page)
			goto out;
H
Hugh Dickins 已提交
537

H
Hugh Dickins 已提交
538
		lock_page(page);
H
Hugh Dickins 已提交
539
		hlist_del(&rmap_item->hlist);
H
Hugh Dickins 已提交
540 541
		unlock_page(page);
		put_page(page);
542

H
Hugh Dickins 已提交
543 544 545
		if (stable_node->hlist.first)
			ksm_pages_sharing--;
		else
H
Hugh Dickins 已提交
546
			ksm_pages_shared--;
I
Izik Eidus 已提交
547

548
		put_anon_vma(rmap_item->anon_vma);
549
		rmap_item->address &= PAGE_MASK;
I
Izik Eidus 已提交
550

H
Hugh Dickins 已提交
551
	} else if (rmap_item->address & UNSTABLE_FLAG) {
I
Izik Eidus 已提交
552 553
		unsigned char age;
		/*
H
Hugh Dickins 已提交
554
		 * Usually ksmd can and must skip the rb_erase, because
I
Izik Eidus 已提交
555
		 * root_unstable_tree was already reset to RB_ROOT.
H
Hugh Dickins 已提交
556 557 558
		 * 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
559 560
		 */
		age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
561
		BUG_ON(age > 1);
I
Izik Eidus 已提交
562 563
		if (!age)
			rb_erase(&rmap_item->node, &root_unstable_tree);
564

565
		ksm_pages_unshared--;
566
		rmap_item->address &= PAGE_MASK;
I
Izik Eidus 已提交
567
	}
H
Hugh Dickins 已提交
568
out:
I
Izik Eidus 已提交
569 570 571 572
	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
573
				       struct rmap_item **rmap_list)
I
Izik Eidus 已提交
574
{
H
Hugh Dickins 已提交
575 576 577
	while (*rmap_list) {
		struct rmap_item *rmap_item = *rmap_list;
		*rmap_list = rmap_item->rmap_list;
I
Izik Eidus 已提交
578 579 580 581 582 583 584 585 586 587 588 589
		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
590 591 592 593 594
 *
 * 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
595
 */
H
Hugh Dickins 已提交
596 597
static int unmerge_ksm_pages(struct vm_area_struct *vma,
			     unsigned long start, unsigned long end)
I
Izik Eidus 已提交
598 599
{
	unsigned long addr;
H
Hugh Dickins 已提交
600
	int err = 0;
I
Izik Eidus 已提交
601

H
Hugh Dickins 已提交
602
	for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
H
Hugh Dickins 已提交
603 604
		if (ksm_test_exit(vma->vm_mm))
			break;
H
Hugh Dickins 已提交
605 606 607 608 609 610
		if (signal_pending(current))
			err = -ERESTARTSYS;
		else
			err = break_ksm(vma, addr);
	}
	return err;
I
Izik Eidus 已提交
611 612
}

H
Hugh Dickins 已提交
613 614 615 616
#ifdef CONFIG_SYSFS
/*
 * Only called through the sysfs control interface:
 */
H
Hugh Dickins 已提交
617
static int unmerge_and_remove_all_rmap_items(void)
I
Izik Eidus 已提交
618 619 620 621
{
	struct mm_slot *mm_slot;
	struct mm_struct *mm;
	struct vm_area_struct *vma;
H
Hugh Dickins 已提交
622 623 624
	int err = 0;

	spin_lock(&ksm_mmlist_lock);
H
Hugh Dickins 已提交
625
	ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
H
Hugh Dickins 已提交
626 627
						struct mm_slot, mm_list);
	spin_unlock(&ksm_mmlist_lock);
I
Izik Eidus 已提交
628

H
Hugh Dickins 已提交
629 630
	for (mm_slot = ksm_scan.mm_slot;
			mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
I
Izik Eidus 已提交
631 632 633
		mm = mm_slot->mm;
		down_read(&mm->mmap_sem);
		for (vma = mm->mmap; vma; vma = vma->vm_next) {
H
Hugh Dickins 已提交
634 635
			if (ksm_test_exit(mm))
				break;
I
Izik Eidus 已提交
636 637
			if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
				continue;
H
Hugh Dickins 已提交
638 639
			err = unmerge_ksm_pages(vma,
						vma->vm_start, vma->vm_end);
H
Hugh Dickins 已提交
640 641
			if (err)
				goto error;
I
Izik Eidus 已提交
642
		}
H
Hugh Dickins 已提交
643

H
Hugh Dickins 已提交
644
		remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
H
Hugh Dickins 已提交
645 646

		spin_lock(&ksm_mmlist_lock);
H
Hugh Dickins 已提交
647
		ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
H
Hugh Dickins 已提交
648
						struct mm_slot, mm_list);
H
Hugh Dickins 已提交
649 650 651 652 653 654 655 656 657 658 659 660 661
		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
662 663
	}

H
Hugh Dickins 已提交
664
	ksm_scan.seqnr = 0;
H
Hugh Dickins 已提交
665 666 667 668
	return 0;

error:
	up_read(&mm->mmap_sem);
I
Izik Eidus 已提交
669
	spin_lock(&ksm_mmlist_lock);
H
Hugh Dickins 已提交
670
	ksm_scan.mm_slot = &ksm_mm_head;
I
Izik Eidus 已提交
671
	spin_unlock(&ksm_mmlist_lock);
H
Hugh Dickins 已提交
672
	return err;
I
Izik Eidus 已提交
673
}
H
Hugh Dickins 已提交
674
#endif /* CONFIG_SYSFS */
I
Izik Eidus 已提交
675 676 677 678

static u32 calc_checksum(struct page *page)
{
	u32 checksum;
679
	void *addr = kmap_atomic(page);
I
Izik Eidus 已提交
680
	checksum = jhash2(addr, PAGE_SIZE / 4, 17);
681
	kunmap_atomic(addr);
I
Izik Eidus 已提交
682 683 684 685 686 687 688 689
	return checksum;
}

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

690 691
	addr1 = kmap_atomic(page1);
	addr2 = kmap_atomic(page2);
I
Izik Eidus 已提交
692
	ret = memcmp(addr1, addr2, PAGE_SIZE);
693 694
	kunmap_atomic(addr2);
	kunmap_atomic(addr1);
I
Izik Eidus 已提交
695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716
	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;

A
Andrea Arcangeli 已提交
717
	BUG_ON(PageTransCompound(page));
I
Izik Eidus 已提交
718 719 720 721
	ptep = page_check_address(page, mm, addr, &ptl, 0);
	if (!ptep)
		goto out;

722
	if (pte_write(*ptep) || pte_dirty(*ptep)) {
I
Izik Eidus 已提交
723 724 725 726 727
		pte_t entry;

		swapped = PageSwapCache(page);
		flush_cache_page(vma, addr, page_to_pfn(page));
		/*
L
Lucas De Marchi 已提交
728
		 * Ok this is tricky, when get_user_pages_fast() run it doesn't
I
Izik Eidus 已提交
729 730 731 732 733 734 735 736 737 738 739 740
		 * 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
		 */
741
		if (page_mapcount(page) + 1 + swapped != page_count(page)) {
742
			set_pte_at(mm, addr, ptep, entry);
I
Izik Eidus 已提交
743 744
			goto out_unlock;
		}
745 746 747
		if (pte_dirty(entry))
			set_page_dirty(page);
		entry = pte_mkclean(pte_wrprotect(entry));
I
Izik Eidus 已提交
748 749 750 751 752 753 754 755 756 757 758 759 760
		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
761 762 763
 * @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
764 765 766 767
 * @orig_pte: the original value of the pte
 *
 * Returns 0 on success, -EFAULT on failure.
 */
768 769
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
770 771 772 773 774 775 776 777 778 779
{
	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;

780
	addr = page_address_in_vma(page, vma);
I
Izik Eidus 已提交
781 782 783 784 785 786 787 788 789 790 791 792
	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);
A
Andrea Arcangeli 已提交
793
	BUG_ON(pmd_trans_huge(*pmd));
I
Izik Eidus 已提交
794 795 796 797 798 799 800 801 802
	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;
	}

803
	get_page(kpage);
H
Hugh Dickins 已提交
804
	page_add_anon_rmap(kpage, vma, addr);
I
Izik Eidus 已提交
805 806 807

	flush_cache_page(vma, addr, pte_pfn(*ptep));
	ptep_clear_flush(vma, addr, ptep);
808
	set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
I
Izik Eidus 已提交
809

810
	page_remove_rmap(page);
811 812
	if (!page_mapped(page))
		try_to_free_swap(page);
813
	put_page(page);
I
Izik Eidus 已提交
814 815 816 817 818 819 820

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

A
Andrea Arcangeli 已提交
821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847
static int page_trans_compound_anon_split(struct page *page)
{
	int ret = 0;
	struct page *transhuge_head = page_trans_compound_anon(page);
	if (transhuge_head) {
		/* Get the reference on the head to split it. */
		if (get_page_unless_zero(transhuge_head)) {
			/*
			 * Recheck we got the reference while the head
			 * was still anonymous.
			 */
			if (PageAnon(transhuge_head))
				ret = split_huge_page(transhuge_head);
			else
				/*
				 * Retry later if split_huge_page run
				 * from under us.
				 */
				ret = 1;
			put_page(transhuge_head);
		} else
			/* Retry later if split_huge_page run from under us. */
			ret = 1;
	}
	return ret;
}

I
Izik Eidus 已提交
848 849
/*
 * try_to_merge_one_page - take two pages and merge them into one
850 851
 * @vma: the vma that holds the pte pointing to page
 * @page: the PageAnon page that we want to replace with kpage
852 853
 * @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
854 855 856 857
 *
 * This function returns 0 if the pages were merged, -EFAULT otherwise.
 */
static int try_to_merge_one_page(struct vm_area_struct *vma,
858
				 struct page *page, struct page *kpage)
I
Izik Eidus 已提交
859 860 861 862
{
	pte_t orig_pte = __pte(0);
	int err = -EFAULT;

H
Hugh Dickins 已提交
863 864 865
	if (page == kpage)			/* ksm page forked */
		return 0;

I
Izik Eidus 已提交
866 867
	if (!(vma->vm_flags & VM_MERGEABLE))
		goto out;
A
Andrea Arcangeli 已提交
868 869 870
	if (PageTransCompound(page) && page_trans_compound_anon_split(page))
		goto out;
	BUG_ON(PageTransCompound(page));
871
	if (!PageAnon(page))
I
Izik Eidus 已提交
872 873 874 875 876 877 878 879 880
		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.
	 */
881
	if (!trylock_page(page))
882
		goto out;
I
Izik Eidus 已提交
883 884 885 886 887 888
	/*
	 * 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.
	 */
889 890 891 892 893 894 895 896 897 898 899 900 901
	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
902

903
	if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
H
Hugh Dickins 已提交
904
		munlock_vma_page(page);
H
Hugh Dickins 已提交
905 906 907 908 909 910 911
		if (!PageMlocked(kpage)) {
			unlock_page(page);
			lock_page(kpage);
			mlock_vma_page(kpage);
			page = kpage;		/* for final unlock */
		}
	}
H
Hugh Dickins 已提交
912

913
	unlock_page(page);
I
Izik Eidus 已提交
914 915 916 917
out:
	return err;
}

H
Hugh Dickins 已提交
918 919 920
/*
 * 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.
921 922
 *
 * This function returns 0 if the pages were merged, -EFAULT otherwise.
H
Hugh Dickins 已提交
923
 */
924 925
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
926
{
927
	struct mm_struct *mm = rmap_item->mm;
H
Hugh Dickins 已提交
928 929 930
	struct vm_area_struct *vma;
	int err = -EFAULT;

931 932
	down_read(&mm->mmap_sem);
	if (ksm_test_exit(mm))
H
Hugh Dickins 已提交
933
		goto out;
934 935
	vma = find_vma(mm, rmap_item->address);
	if (!vma || vma->vm_start > rmap_item->address)
H
Hugh Dickins 已提交
936 937
		goto out;

938
	err = try_to_merge_one_page(vma, page, kpage);
H
Hugh Dickins 已提交
939 940 941 942
	if (err)
		goto out;

	/* Must get reference to anon_vma while still holding mmap_sem */
943 944
	rmap_item->anon_vma = vma->anon_vma;
	get_anon_vma(vma->anon_vma);
H
Hugh Dickins 已提交
945
out:
946
	up_read(&mm->mmap_sem);
H
Hugh Dickins 已提交
947 948 949
	return err;
}

I
Izik Eidus 已提交
950 951 952 953
/*
 * try_to_merge_two_pages - take two identical pages and prepare them
 * to be merged into one page.
 *
954 955
 * This function returns the kpage if we successfully merged two identical
 * pages into one ksm page, NULL otherwise.
I
Izik Eidus 已提交
956
 *
957
 * Note that this function upgrades page to ksm page: if one of the pages
I
Izik Eidus 已提交
958 959
 * is already a ksm page, try_to_merge_with_ksm_page should be used.
 */
960 961 962 963
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
964
{
965
	int err;
I
Izik Eidus 已提交
966

967
	err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
I
Izik Eidus 已提交
968
	if (!err) {
969
		err = try_to_merge_with_ksm_page(tree_rmap_item,
970
							tree_page, page);
I
Izik Eidus 已提交
971
		/*
H
Hugh Dickins 已提交
972 973
		 * If that fails, we have a ksm page with only one pte
		 * pointing to it: so break it.
I
Izik Eidus 已提交
974
		 */
H
Hugh Dickins 已提交
975
		if (err)
976
			break_cow(rmap_item);
I
Izik Eidus 已提交
977
	}
978
	return err ? NULL : page;
I
Izik Eidus 已提交
979 980 981
}

/*
982
 * stable_tree_search - search for page inside the stable tree
I
Izik Eidus 已提交
983 984 985 986
 *
 * 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
987
 * This function returns the stable tree node of identical content if found,
I
Izik Eidus 已提交
988 989
 * NULL otherwise.
 */
990
static struct page *stable_tree_search(struct page *page)
I
Izik Eidus 已提交
991 992
{
	struct rb_node *node = root_stable_tree.rb_node;
H
Hugh Dickins 已提交
993
	struct stable_node *stable_node;
I
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994

995 996 997
	stable_node = page_stable_node(page);
	if (stable_node) {			/* ksm page forked */
		get_page(page);
998
		return page;
999 1000
	}

I
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1001
	while (node) {
H
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1002
		struct page *tree_page;
I
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1003 1004
		int ret;

1005
		cond_resched();
H
Hugh Dickins 已提交
1006
		stable_node = rb_entry(node, struct stable_node, node);
H
Hugh Dickins 已提交
1007 1008 1009
		tree_page = get_ksm_page(stable_node);
		if (!tree_page)
			return NULL;
I
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1010

H
Hugh Dickins 已提交
1011
		ret = memcmp_pages(page, tree_page);
I
Izik Eidus 已提交
1012

H
Hugh Dickins 已提交
1013 1014
		if (ret < 0) {
			put_page(tree_page);
I
Izik Eidus 已提交
1015
			node = node->rb_left;
H
Hugh Dickins 已提交
1016 1017
		} else if (ret > 0) {
			put_page(tree_page);
I
Izik Eidus 已提交
1018
			node = node->rb_right;
H
Hugh Dickins 已提交
1019
		} else
1020
			return tree_page;
I
Izik Eidus 已提交
1021 1022 1023 1024 1025 1026 1027 1028 1029
	}

	return NULL;
}

/*
 * stable_tree_insert - insert rmap_item pointing to new ksm page
 * into the stable tree.
 *
H
Hugh Dickins 已提交
1030 1031
 * This function returns the stable tree node just allocated on success,
 * NULL otherwise.
I
Izik Eidus 已提交
1032
 */
H
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1033
static struct stable_node *stable_tree_insert(struct page *kpage)
I
Izik Eidus 已提交
1034 1035 1036
{
	struct rb_node **new = &root_stable_tree.rb_node;
	struct rb_node *parent = NULL;
H
Hugh Dickins 已提交
1037
	struct stable_node *stable_node;
I
Izik Eidus 已提交
1038 1039

	while (*new) {
H
Hugh Dickins 已提交
1040
		struct page *tree_page;
I
Izik Eidus 已提交
1041 1042
		int ret;

1043
		cond_resched();
H
Hugh Dickins 已提交
1044
		stable_node = rb_entry(*new, struct stable_node, node);
H
Hugh Dickins 已提交
1045 1046 1047
		tree_page = get_ksm_page(stable_node);
		if (!tree_page)
			return NULL;
I
Izik Eidus 已提交
1048

H
Hugh Dickins 已提交
1049 1050
		ret = memcmp_pages(kpage, tree_page);
		put_page(tree_page);
I
Izik Eidus 已提交
1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066

		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;
		}
	}

H
Hugh Dickins 已提交
1067 1068 1069
	stable_node = alloc_stable_node();
	if (!stable_node)
		return NULL;
I
Izik Eidus 已提交
1070

H
Hugh Dickins 已提交
1071 1072 1073 1074 1075
	rb_link_node(&stable_node->node, parent, new);
	rb_insert_color(&stable_node->node, &root_stable_tree);

	INIT_HLIST_HEAD(&stable_node->hlist);

1076
	stable_node->kpfn = page_to_pfn(kpage);
1077 1078
	set_page_stable_node(kpage, stable_node);

H
Hugh Dickins 已提交
1079
	return stable_node;
I
Izik Eidus 已提交
1080 1081 1082
}

/*
1083 1084
 * unstable_tree_search_insert - search for identical page,
 * else insert rmap_item into the unstable tree.
I
Izik Eidus 已提交
1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095
 *
 * 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.
 */
1096 1097 1098 1099 1100
static
struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
					      struct page *page,
					      struct page **tree_pagep)

I
Izik Eidus 已提交
1101 1102 1103 1104 1105 1106
{
	struct rb_node **new = &root_unstable_tree.rb_node;
	struct rb_node *parent = NULL;

	while (*new) {
		struct rmap_item *tree_rmap_item;
1107
		struct page *tree_page;
I
Izik Eidus 已提交
1108 1109
		int ret;

H
Hugh Dickins 已提交
1110
		cond_resched();
I
Izik Eidus 已提交
1111
		tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1112
		tree_page = get_mergeable_page(tree_rmap_item);
1113
		if (IS_ERR_OR_NULL(tree_page))
I
Izik Eidus 已提交
1114 1115 1116
			return NULL;

		/*
1117
		 * Don't substitute a ksm page for a forked page.
I
Izik Eidus 已提交
1118
		 */
1119 1120
		if (page == tree_page) {
			put_page(tree_page);
I
Izik Eidus 已提交
1121 1122 1123
			return NULL;
		}

1124
		ret = memcmp_pages(page, tree_page);
I
Izik Eidus 已提交
1125 1126 1127

		parent = *new;
		if (ret < 0) {
1128
			put_page(tree_page);
I
Izik Eidus 已提交
1129 1130
			new = &parent->rb_left;
		} else if (ret > 0) {
1131
			put_page(tree_page);
I
Izik Eidus 已提交
1132 1133
			new = &parent->rb_right;
		} else {
1134
			*tree_pagep = tree_page;
I
Izik Eidus 已提交
1135 1136 1137 1138
			return tree_rmap_item;
		}
	}

H
Hugh Dickins 已提交
1139
	rmap_item->address |= UNSTABLE_FLAG;
I
Izik Eidus 已提交
1140 1141 1142 1143
	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);

1144
	ksm_pages_unshared++;
I
Izik Eidus 已提交
1145 1146 1147 1148 1149 1150 1151 1152 1153
	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
1154
			       struct stable_node *stable_node)
I
Izik Eidus 已提交
1155
{
H
Hugh Dickins 已提交
1156
	rmap_item->head = stable_node;
I
Izik Eidus 已提交
1157
	rmap_item->address |= STABLE_FLAG;
H
Hugh Dickins 已提交
1158
	hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
H
Hugh Dickins 已提交
1159

H
Hugh Dickins 已提交
1160 1161 1162 1163
	if (rmap_item->hlist.next)
		ksm_pages_sharing++;
	else
		ksm_pages_shared++;
I
Izik Eidus 已提交
1164 1165 1166
}

/*
H
Hugh Dickins 已提交
1167 1168 1169 1170
 * 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
Izik Eidus 已提交
1171 1172 1173 1174 1175 1176 1177
 *
 * @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;
1178
	struct page *tree_page = NULL;
H
Hugh Dickins 已提交
1179
	struct stable_node *stable_node;
1180
	struct page *kpage;
I
Izik Eidus 已提交
1181 1182 1183
	unsigned int checksum;
	int err;

1184
	remove_rmap_item_from_tree(rmap_item);
I
Izik Eidus 已提交
1185 1186

	/* We first start with searching the page inside the stable tree */
1187 1188
	kpage = stable_tree_search(page);
	if (kpage) {
1189
		err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
I
Izik Eidus 已提交
1190 1191 1192 1193 1194
		if (!err) {
			/*
			 * The page was successfully merged:
			 * add its rmap_item to the stable tree.
			 */
H
Hugh Dickins 已提交
1195
			lock_page(kpage);
1196
			stable_tree_append(rmap_item, page_stable_node(kpage));
H
Hugh Dickins 已提交
1197
			unlock_page(kpage);
I
Izik Eidus 已提交
1198
		}
1199
		put_page(kpage);
I
Izik Eidus 已提交
1200 1201 1202 1203
		return;
	}

	/*
H
Hugh Dickins 已提交
1204 1205 1206 1207
	 * 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
Izik Eidus 已提交
1208 1209 1210 1211 1212 1213 1214
	 */
	checksum = calc_checksum(page);
	if (rmap_item->oldchecksum != checksum) {
		rmap_item->oldchecksum = checksum;
		return;
	}

1215 1216
	tree_rmap_item =
		unstable_tree_search_insert(rmap_item, page, &tree_page);
I
Izik Eidus 已提交
1217
	if (tree_rmap_item) {
1218 1219 1220
		kpage = try_to_merge_two_pages(rmap_item, page,
						tree_rmap_item, tree_page);
		put_page(tree_page);
I
Izik Eidus 已提交
1221 1222 1223 1224 1225
		/*
		 * 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.
		 */
1226
		if (kpage) {
1227
			remove_rmap_item_from_tree(tree_rmap_item);
1228

H
Hugh Dickins 已提交
1229
			lock_page(kpage);
H
Hugh Dickins 已提交
1230 1231 1232 1233 1234
			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
1235
			unlock_page(kpage);
H
Hugh Dickins 已提交
1236

I
Izik Eidus 已提交
1237 1238 1239 1240 1241 1242
			/*
			 * 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
1243
			if (!stable_node) {
1244 1245
				break_cow(tree_rmap_item);
				break_cow(rmap_item);
I
Izik Eidus 已提交
1246 1247 1248 1249 1250 1251
			}
		}
	}
}

static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
H
Hugh Dickins 已提交
1252
					    struct rmap_item **rmap_list,
I
Izik Eidus 已提交
1253 1254 1255 1256
					    unsigned long addr)
{
	struct rmap_item *rmap_item;

H
Hugh Dickins 已提交
1257 1258
	while (*rmap_list) {
		rmap_item = *rmap_list;
1259
		if ((rmap_item->address & PAGE_MASK) == addr)
I
Izik Eidus 已提交
1260 1261 1262
			return rmap_item;
		if (rmap_item->address > addr)
			break;
H
Hugh Dickins 已提交
1263
		*rmap_list = rmap_item->rmap_list;
I
Izik Eidus 已提交
1264 1265 1266 1267 1268 1269 1270 1271 1272
		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
1273 1274
		rmap_item->rmap_list = *rmap_list;
		*rmap_list = rmap_item;
I
Izik Eidus 已提交
1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290
	}
	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) {
H
Hugh Dickins 已提交
1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302
		/*
		 * A number of pages can hang around indefinitely on per-cpu
		 * pagevecs, raised page count preventing write_protect_page
		 * from merging them.  Though it doesn't really matter much,
		 * it is puzzling to see some stuck in pages_volatile until
		 * other activity jostles them out, and they also prevented
		 * LTP's KSM test from succeeding deterministically; so drain
		 * them here (here rather than on entry to ksm_do_scan(),
		 * so we don't IPI too often when pages_to_scan is set low).
		 */
		lru_add_drain_all();

I
Izik Eidus 已提交
1303 1304 1305 1306 1307 1308
		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);
1309 1310 1311 1312 1313 1314
		/*
		 * Although we tested list_empty() above, a racing __ksm_exit
		 * of the last mm on the list may have removed it since then.
		 */
		if (slot == &ksm_mm_head)
			return NULL;
I
Izik Eidus 已提交
1315 1316
next_mm:
		ksm_scan.address = 0;
H
Hugh Dickins 已提交
1317
		ksm_scan.rmap_list = &slot->rmap_list;
I
Izik Eidus 已提交
1318 1319 1320 1321
	}

	mm = slot->mm;
	down_read(&mm->mmap_sem);
H
Hugh Dickins 已提交
1322 1323 1324 1325 1326 1327
	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
1328 1329 1330 1331 1332 1333 1334 1335
		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
1336 1337
			if (ksm_test_exit(mm))
				break;
I
Izik Eidus 已提交
1338
			*page = follow_page(vma, ksm_scan.address, FOLL_GET);
1339 1340 1341 1342 1343
			if (IS_ERR_OR_NULL(*page)) {
				ksm_scan.address += PAGE_SIZE;
				cond_resched();
				continue;
			}
A
Andrea Arcangeli 已提交
1344 1345
			if (PageAnon(*page) ||
			    page_trans_compound_anon(*page)) {
I
Izik Eidus 已提交
1346 1347 1348
				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
1349
					ksm_scan.rmap_list, ksm_scan.address);
I
Izik Eidus 已提交
1350
				if (rmap_item) {
H
Hugh Dickins 已提交
1351 1352
					ksm_scan.rmap_list =
							&rmap_item->rmap_list;
I
Izik Eidus 已提交
1353 1354 1355 1356 1357 1358
					ksm_scan.address += PAGE_SIZE;
				} else
					put_page(*page);
				up_read(&mm->mmap_sem);
				return rmap_item;
			}
1359
			put_page(*page);
I
Izik Eidus 已提交
1360 1361 1362 1363 1364
			ksm_scan.address += PAGE_SIZE;
			cond_resched();
		}
	}

H
Hugh Dickins 已提交
1365 1366
	if (ksm_test_exit(mm)) {
		ksm_scan.address = 0;
H
Hugh Dickins 已提交
1367
		ksm_scan.rmap_list = &slot->rmap_list;
H
Hugh Dickins 已提交
1368
	}
I
Izik Eidus 已提交
1369 1370 1371 1372
	/*
	 * 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
1373
	remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
I
Izik Eidus 已提交
1374 1375

	spin_lock(&ksm_mmlist_lock);
1376 1377 1378 1379 1380 1381 1382
	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
1383 1384 1385 1386
		 * 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).
1387 1388 1389
		 */
		hlist_del(&slot->link);
		list_del(&slot->mm_list);
H
Hugh Dickins 已提交
1390 1391
		spin_unlock(&ksm_mmlist_lock);

1392 1393
		free_mm_slot(slot);
		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
H
Hugh Dickins 已提交
1394 1395 1396 1397 1398
		up_read(&mm->mmap_sem);
		mmdrop(mm);
	} else {
		spin_unlock(&ksm_mmlist_lock);
		up_read(&mm->mmap_sem);
1399
	}
I
Izik Eidus 已提交
1400 1401

	/* Repeat until we've completed scanning the whole list */
1402
	slot = ksm_scan.mm_slot;
I
Izik Eidus 已提交
1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416
	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;
1417
	struct page *uninitialized_var(page);
I
Izik Eidus 已提交
1418

1419
	while (scan_npages-- && likely(!freezing(current))) {
I
Izik Eidus 已提交
1420 1421 1422 1423 1424 1425 1426 1427 1428 1429
		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
Hugh Dickins 已提交
1430 1431 1432 1433 1434
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
1435 1436
static int ksm_scan_thread(void *nothing)
{
1437
	set_freezable();
I
Izik Eidus 已提交
1438
	set_user_nice(current, 5);
I
Izik Eidus 已提交
1439 1440

	while (!kthread_should_stop()) {
H
Hugh Dickins 已提交
1441 1442
		mutex_lock(&ksm_thread_mutex);
		if (ksmd_should_run())
I
Izik Eidus 已提交
1443
			ksm_do_scan(ksm_thread_pages_to_scan);
H
Hugh Dickins 已提交
1444 1445
		mutex_unlock(&ksm_thread_mutex);

1446 1447
		try_to_freeze();

H
Hugh Dickins 已提交
1448
		if (ksmd_should_run()) {
I
Izik Eidus 已提交
1449 1450 1451
			schedule_timeout_interruptible(
				msecs_to_jiffies(ksm_thread_sleep_millisecs));
		} else {
1452
			wait_event_freezable(ksm_thread_wait,
H
Hugh Dickins 已提交
1453
				ksmd_should_run() || kthread_should_stop());
I
Izik Eidus 已提交
1454 1455 1456 1457 1458
		}
	}
	return 0;
}

H
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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
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	int err;
H
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1464 1465 1466 1467 1468 1469 1470 1471

	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 |
1472
				 VM_HUGETLB | VM_NONLINEAR | VM_MIXEDMAP))
H
Hugh Dickins 已提交
1473 1474
			return 0;		/* just ignore the advice */

1475 1476 1477 1478 1479
#ifdef VM_SAO
		if (*vm_flags & VM_SAO)
			return 0;
#endif

H
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1480 1481 1482 1483 1484
		if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
			err = __ksm_enter(mm);
			if (err)
				return err;
		}
H
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1485 1486 1487 1488 1489 1490 1491 1492

		*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
1493 1494 1495 1496 1497
		if (vma->anon_vma) {
			err = unmerge_ksm_pages(vma, start, end);
			if (err)
				return err;
		}
H
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1498 1499 1500 1501 1502 1503 1504 1505 1506 1507

		*vm_flags &= ~VM_MERGEABLE;
		break;
	}

	return 0;
}

int __ksm_enter(struct mm_struct *mm)
{
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	struct mm_slot *mm_slot;
	int needs_wakeup;

	mm_slot = alloc_mm_slot();
I
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1512 1513 1514
	if (!mm_slot)
		return -ENOMEM;

H
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1515 1516 1517
	/* Check ksm_run too?  Would need tighter locking */
	needs_wakeup = list_empty(&ksm_mm_head.mm_list);

I
Izik Eidus 已提交
1518 1519 1520 1521 1522 1523 1524 1525 1526 1527
	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
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	set_bit(MMF_VM_MERGEABLE, &mm->flags);
H
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1529
	atomic_inc(&mm->mm_count);
H
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1530 1531 1532 1533

	if (needs_wakeup)
		wake_up_interruptible(&ksm_thread_wait);

H
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1534 1535 1536
	return 0;
}

1537
void __ksm_exit(struct mm_struct *mm)
H
Hugh Dickins 已提交
1538
{
1539
	struct mm_slot *mm_slot;
H
Hugh Dickins 已提交
1540
	int easy_to_free = 0;
1541

I
Izik Eidus 已提交
1542
	/*
H
Hugh Dickins 已提交
1543 1544 1545 1546 1547 1548
	 * 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.
I
Izik Eidus 已提交
1549
	 */
H
Hugh Dickins 已提交
1550

1551 1552
	spin_lock(&ksm_mmlist_lock);
	mm_slot = get_mm_slot(mm);
H
Hugh Dickins 已提交
1553
	if (mm_slot && ksm_scan.mm_slot != mm_slot) {
H
Hugh Dickins 已提交
1554
		if (!mm_slot->rmap_list) {
H
Hugh Dickins 已提交
1555 1556 1557 1558 1559 1560 1561
			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);
		}
1562 1563 1564
	}
	spin_unlock(&ksm_mmlist_lock);

H
Hugh Dickins 已提交
1565 1566 1567 1568 1569 1570 1571 1572
	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);
	}
I
Izik Eidus 已提交
1573 1574
}

H
Hugh Dickins 已提交
1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605
struct page *ksm_does_need_to_copy(struct page *page,
			struct vm_area_struct *vma, unsigned long address)
{
	struct page *new_page;

	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);
	}

	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;
H
Hugh Dickins 已提交
1606
	int search_new_forks = 0;
H
Hugh Dickins 已提交
1607 1608 1609 1610 1611 1612 1613

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

	stable_node = page_stable_node(page);
	if (!stable_node)
		return 0;
H
Hugh Dickins 已提交
1614
again:
H
Hugh Dickins 已提交
1615
	hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
H
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1616
		struct anon_vma *anon_vma = rmap_item->anon_vma;
1617
		struct anon_vma_chain *vmac;
H
Hugh Dickins 已提交
1618
		struct vm_area_struct *vma;
H
Hugh Dickins 已提交
1619

1620
		anon_vma_lock(anon_vma);
1621 1622
		list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
			vma = vmac->vma;
H
Hugh Dickins 已提交
1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636
			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;
H
Hugh Dickins 已提交
1637

H
Hugh Dickins 已提交
1638
			referenced += page_referenced_one(page, vma,
H
Hugh Dickins 已提交
1639
				rmap_item->address, &mapcount, vm_flags);
H
Hugh Dickins 已提交
1640 1641 1642
			if (!search_new_forks || !mapcount)
				break;
		}
1643
		anon_vma_unlock(anon_vma);
H
Hugh Dickins 已提交
1644 1645 1646
		if (!mapcount)
			goto out;
	}
H
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1647 1648
	if (!search_new_forks++)
		goto again;
H
Hugh Dickins 已提交
1649 1650 1651 1652 1653 1654 1655 1656 1657 1658
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;
H
Hugh Dickins 已提交
1659
	int search_new_forks = 0;
H
Hugh Dickins 已提交
1660 1661 1662 1663 1664 1665 1666

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

	stable_node = page_stable_node(page);
	if (!stable_node)
		return SWAP_FAIL;
H
Hugh Dickins 已提交
1667
again:
H
Hugh Dickins 已提交
1668
	hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
H
Hugh Dickins 已提交
1669
		struct anon_vma *anon_vma = rmap_item->anon_vma;
1670
		struct anon_vma_chain *vmac;
H
Hugh Dickins 已提交
1671
		struct vm_area_struct *vma;
H
Hugh Dickins 已提交
1672

1673
		anon_vma_lock(anon_vma);
1674 1675
		list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
			vma = vmac->vma;
H
Hugh Dickins 已提交
1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690
			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)) {
1691
				anon_vma_unlock(anon_vma);
H
Hugh Dickins 已提交
1692 1693 1694
				goto out;
			}
		}
1695
		anon_vma_unlock(anon_vma);
H
Hugh Dickins 已提交
1696
	}
H
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1697 1698
	if (!search_new_forks++)
		goto again;
H
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1699 1700 1701 1702
out:
	return ret;
}

1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721
#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;
1722
		struct anon_vma_chain *vmac;
1723 1724
		struct vm_area_struct *vma;

1725
		anon_vma_lock(anon_vma);
1726 1727
		list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
			vma = vmac->vma;
1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741
			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) {
1742
				anon_vma_unlock(anon_vma);
1743 1744 1745
				goto out;
			}
		}
1746
		anon_vma_unlock(anon_vma);
1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763
	}
	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) {
1764 1765
		VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
		stable_node->kpfn = page_to_pfn(newpage);
1766 1767 1768 1769
	}
}
#endif /* CONFIG_MIGRATION */

1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797
#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.
1798 1799 1800 1801 1802
		 * mutex_lock_nested() is necessary because lockdep was alarmed
		 * that here we take ksm_thread_mutex inside notifier chain
		 * mutex, and later take notifier chain mutex inside
		 * ksm_thread_mutex to unlock it.   But that's safe because both
		 * are inside mem_hotplug_mutex.
1803
		 */
1804
		mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825
		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 */

H
Hugh Dickins 已提交
1826 1827 1828 1829 1830
#ifdef CONFIG_SYSFS
/*
 * This all compiles without CONFIG_SYSFS, but is a waste of space.
 */

I
Izik Eidus 已提交
1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873 1874 1875 1876 1877 1878 1879 1880 1881 1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903
#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,
1904 1905
	 * breaking COW to free the pages_shared (but leaves mm_slots
	 * on the list for when ksmd may be set running again).
I
Izik Eidus 已提交
1906 1907 1908 1909 1910
	 */

	mutex_lock(&ksm_thread_mutex);
	if (ksm_run != flags) {
		ksm_run = flags;
H
Hugh Dickins 已提交
1911
		if (flags & KSM_RUN_UNMERGE) {
1912 1913 1914
			int oom_score_adj;

			oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
H
Hugh Dickins 已提交
1915
			err = unmerge_and_remove_all_rmap_items();
1916 1917
			compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX,
								oom_score_adj);
H
Hugh Dickins 已提交
1918 1919 1920 1921 1922
			if (err) {
				ksm_run = KSM_RUN_STOP;
				count = err;
			}
		}
I
Izik Eidus 已提交
1923 1924 1925 1926 1927 1928 1929 1930 1931 1932
	}
	mutex_unlock(&ksm_thread_mutex);

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

	return count;
}
KSM_ATTR(run);

1933 1934 1935 1936 1937 1938 1939 1940 1941 1942
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)
{
H
Hugh Dickins 已提交
1943
	return sprintf(buf, "%lu\n", ksm_pages_sharing);
1944 1945 1946
}
KSM_ATTR_RO(pages_sharing);

1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977
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);

I
Izik Eidus 已提交
1978 1979 1980 1981
static struct attribute *ksm_attrs[] = {
	&sleep_millisecs_attr.attr,
	&pages_to_scan_attr.attr,
	&run_attr.attr,
1982 1983
	&pages_shared_attr.attr,
	&pages_sharing_attr.attr,
1984 1985 1986
	&pages_unshared_attr.attr,
	&pages_volatile_attr.attr,
	&full_scans_attr.attr,
I
Izik Eidus 已提交
1987 1988 1989 1990 1991 1992 1993
	NULL,
};

static struct attribute_group ksm_attr_group = {
	.attrs = ksm_attrs,
	.name = "ksm",
};
H
Hugh Dickins 已提交
1994
#endif /* CONFIG_SYSFS */
I
Izik Eidus 已提交
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

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

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

	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);
L
Lai Jiangshan 已提交
2009
		goto out_free;
I
Izik Eidus 已提交
2010 2011
	}

H
Hugh Dickins 已提交
2012
#ifdef CONFIG_SYSFS
I
Izik Eidus 已提交
2013 2014 2015
	err = sysfs_create_group(mm_kobj, &ksm_attr_group);
	if (err) {
		printk(KERN_ERR "ksm: register sysfs failed\n");
H
Hugh Dickins 已提交
2016
		kthread_stop(ksm_thread);
L
Lai Jiangshan 已提交
2017
		goto out_free;
I
Izik Eidus 已提交
2018
	}
H
Hugh Dickins 已提交
2019 2020 2021
#else
	ksm_run = KSM_RUN_MERGE;	/* no way for user to start it */

H
Hugh Dickins 已提交
2022
#endif /* CONFIG_SYSFS */
I
Izik Eidus 已提交
2023

2024 2025 2026 2027 2028 2029 2030
#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
I
Izik Eidus 已提交
2031 2032
	return 0;

L
Lai Jiangshan 已提交
2033
out_free:
I
Izik Eidus 已提交
2034 2035 2036
	ksm_slab_free();
out:
	return err;
H
Hugh Dickins 已提交
2037
}
I
Izik Eidus 已提交
2038
module_init(ksm_init)