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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()
*
* Copyright (C) 2008-2009 Red Hat, Inc.
* Authors:
* Izik Eidus
* Andrea Arcangeli
* Chris Wright
* Hugh Dickins
*
* This work is licensed under the terms of the GNU GPL, version 2.
*/

#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/mman.h>
#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/memory.h>
#include <linux/mmu_notifier.h>
#include <linux/swap.h>
#include <linux/ksm.h>
#include <linux/hash.h>
#include <linux/freezer.h>
#include <linux/oom.h>

#include <asm/tlbflush.h>
#include "internal.h"

/*
* 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
* @rmap_list: head for this mm_slot's singly-linked list of rmap_items
* @mm: the mm that this information is valid for
*/
struct mm_slot {
struct hlist_node link;
struct list_head mm_list;
struct rmap_item *rmap_list;
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
* @rmap_list: link to the next rmap to be scanned in the rmap_list
* @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;
struct rmap_item **rmap_list;
unsigned long seqnr;
};

/**
* 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
* @kpfn: page frame number of this ksm page
*/
struct stable_node {
struct rb_node node;
struct hlist_head hlist;
unsigned long kpfn;
};

/**
* struct rmap_item - reverse mapping item for virtual addresses
* @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
* @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
* @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
* @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
*/
struct rmap_item {
struct rmap_item *rmap_list;
struct anon_vma *anon_vma; /* when stable */
struct mm_struct *mm;
unsigned long address; /* + low bits used for flags below */
unsigned int oldchecksum; /* when unstable */
union {
struct rb_node node; /* when node of unstable tree */
struct { /* when listed from stable tree */
struct stable_node *head;
struct hlist_node hlist;
};
};
};

#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
#define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
#define STABLE_FLAG 0x200 /* is listed from the stable tree */

/* 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_SHIFT 10
#define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT)
static struct hlist_head mm_slots_hash[MM_SLOTS_HASH_HEADS];

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

/* The number of nodes in the stable tree */
static unsigned long ksm_pages_shared;

/* The number of page slots additionally sharing those nodes */
static unsigned long ksm_pages_sharing;

/* 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;

/* Number of pages ksmd should scan in one batch */
static unsigned int ksm_thread_pages_to_scan = 100;

/* Milliseconds ksmd should sleep between batches */
static unsigned int ksm_thread_sleep_millisecs = 20;

#define KSM_RUN_STOP 0
#define KSM_RUN_MERGE 1
#define KSM_RUN_UNMERGE 2
static unsigned int ksm_run = KSM_RUN_STOP;

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;

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

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

return 0;

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

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

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

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

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

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);
}

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;

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

/*
* 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;
}

/*
* 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.
*/
static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
{
struct page *page;
int ret = 0;

do {
cond_resched();
page = follow_page(vma, addr, FOLL_GET);
if (IS_ERR_OR_NULL(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);
} 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;
}

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

/*
* 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.
*/
put_anon_vma(rmap_item->anon_vma);

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

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

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);
if (ksm_test_exit(mm))
goto out;
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 (IS_ERR_OR_NULL(page))
goto out;
if (PageAnon(page) || page_trans_compound_anon(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;
}

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--;
put_anon_vma(rmap_item->anon_vma);
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 = pfn_to_page(stable_node->kpfn);
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;
}

/*
* 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)
{
if (rmap_item->address & STABLE_FLAG) {
struct stable_node *stable_node;
struct page *page;

stable_node = rmap_item->head;
page = get_ksm_page(stable_node);
if (!page)
goto out;

lock_page(page);
hlist_del(&rmap_item->hlist);
unlock_page(page);
put_page(page);

if (stable_node->hlist.first)
ksm_pages_sharing--;
else
ksm_pages_shared--;

put_anon_vma(rmap_item->anon_vma);
rmap_item->address &= PAGE_MASK;

} else if (rmap_item->address & UNSTABLE_FLAG) {
unsigned char age;
/*
* Usually ksmd can and must skip the rb_erase, because
* root_unstable_tree was already reset to RB_ROOT.
* 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.
*/
age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
BUG_ON(age > 1);
if (!age)
rb_erase(&rmap_item->node, &root_unstable_tree);

ksm_pages_unshared--;
rmap_item->address &= PAGE_MASK;
}
out:
cond_resched(); /* we're called from many long loops */
}

static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
struct rmap_item **rmap_list)
{
while (*rmap_list) {
struct rmap_item *rmap_item = *rmap_list;
*rmap_list = rmap_item->rmap_list;
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).
*
* 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.
*/
static int unmerge_ksm_pages(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
unsigned long addr;
int err = 0;

for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
if (ksm_test_exit(vma->vm_mm))
break;
if (signal_pending(current))
err = -ERESTARTSYS;
else
err = break_ksm(vma, addr);
}
return err;
}

#ifdef CONFIG_SYSFS
/*
* Only called through the sysfs control interface:
*/
static int unmerge_and_remove_all_rmap_items(void)
{
struct mm_slot *mm_slot;
struct mm_struct *mm;
struct vm_area_struct *vma;
int err = 0;

spin_lock(&ksm_mmlist_lock);
ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
struct mm_slot, mm_list);
spin_unlock(&ksm_mmlist_lock);

for (mm_slot = ksm_scan.mm_slot;
mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
mm = mm_slot->mm;
down_read(&mm->mmap_sem);
for (vma = mm->mmap; vma; vma = vma->vm_next) {
if (ksm_test_exit(mm))
break;
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
continue;
err = unmerge_ksm_pages(vma,
vma->vm_start, vma->vm_end);
if (err)
goto error;
}

remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);

spin_lock(&ksm_mmlist_lock);
ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
struct mm_slot, mm_list);
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);
}
}

ksm_scan.seqnr = 0;
return 0;

error:
up_read(&mm->mmap_sem);
spin_lock(&ksm_mmlist_lock);
ksm_scan.mm_slot = &ksm_mm_head;
spin_unlock(&ksm_mmlist_lock);
return err;
}
#endif /* CONFIG_SYSFS */

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;

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

if (pte_write(*ptep) || pte_dirty(*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 doesn't
* 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
*/
if (page_mapcount(page) + 1 + swapped != page_count(page)) {
set_pte_at(mm, addr, ptep, entry);
goto out_unlock;
}
if (pte_dirty(entry))
set_page_dirty(page);
entry = pte_mkclean(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
* @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
* @orig_pte: the original value of the pte
*
* Returns 0 on success, -EFAULT on failure.
*/
static int replace_page(struct vm_area_struct *vma, struct page *page,
struct page *kpage, pte_t orig_pte)
{
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;

addr = page_address_in_vma(page, vma);
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);
BUG_ON(pmd_trans_huge(*pmd));
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;
}

get_page(kpage);
page_add_anon_rmap(kpage, vma, addr);

flush_cache_page(vma, addr, pte_pfn(*ptep));
ptep_clear_flush(vma, addr, ptep);
set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));

page_remove_rmap(page);
if (!page_mapped(page))
try_to_free_swap(page);
put_page(page);

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

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;
}

/*
* try_to_merge_one_page - take two pages and merge them into one
* @vma: the vma that holds the pte pointing to page
* @page: the PageAnon page that we want to replace with kpage
* @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.
*
* This function returns 0 if the pages were merged, -EFAULT otherwise.
*/
static int try_to_merge_one_page(struct vm_area_struct *vma,
struct page *page, struct page *kpage)
{
pte_t orig_pte = __pte(0);
int err = -EFAULT;

if (page == kpage) /* ksm page forked */
return 0;

if (!(vma->vm_flags & VM_MERGEABLE))
goto out;
if (PageTransCompound(page) && page_trans_compound_anon_split(page))
goto out;
BUG_ON(PageTransCompound(page));
if (!PageAnon(page))
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.
*/
if (!trylock_page(page))
goto out;
/*
* 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.
*/
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);
}

if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
munlock_vma_page(page);
if (!PageMlocked(kpage)) {
unlock_page(page);
lock_page(kpage);
mlock_vma_page(kpage);
page = kpage; /* for final unlock */
}
}

unlock_page(page);
out:
return err;
}

/*
* 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.
*
* This function returns 0 if the pages were merged, -EFAULT otherwise.
*/
static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
struct page *page, struct page *kpage)
{
struct mm_struct *mm = rmap_item->mm;
struct vm_area_struct *vma;
int err = -EFAULT;

down_read(&mm->mmap_sem);
if (ksm_test_exit(mm))
goto out;
vma = find_vma(mm, rmap_item->address);
if (!vma || vma->vm_start > rmap_item->address)
goto out;

err = try_to_merge_one_page(vma, page, kpage);
if (err)
goto out;

/* Must get reference to anon_vma while still holding mmap_sem */
rmap_item->anon_vma = vma->anon_vma;
get_anon_vma(vma->anon_vma);
out:
up_read(&mm->mmap_sem);
return err;
}

/*
* try_to_merge_two_pages - take two identical pages and prepare them
* to be merged into one page.
*
* This function returns the kpage if we successfully merged two identical
* pages into one ksm page, NULL otherwise.
*
* Note that this function upgrades page to ksm page: if one of the pages
* is already a ksm page, try_to_merge_with_ksm_page should be used.
*/
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)
{
int err;

err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
if (!err) {
err = try_to_merge_with_ksm_page(tree_rmap_item,
tree_page, page);
/*
* If that fails, we have a ksm page with only one pte
* pointing to it: so break it.
*/
if (err)
break_cow(rmap_item);
}
return err ? NULL : page;
}

/*
* stable_tree_search - search for page inside the stable tree
*
* This function checks if there is a page inside the stable tree
* with identical content to the page that we are scanning right now.
*
* This function returns the stable tree node of identical content if found,
* NULL otherwise.
*/
static struct page *stable_tree_search(struct page *page)
{
struct rb_node *node = root_stable_tree.rb_node;
struct stable_node *stable_node;

stable_node = page_stable_node(page);
if (stable_node) { /* ksm page forked */
get_page(page);
return page;
}

while (node) {
struct page *tree_page;
int ret;

cond_resched();
stable_node = rb_entry(node, struct stable_node, node);
tree_page = get_ksm_page(stable_node);
if (!tree_page)
return NULL;

ret = memcmp_pages(page, tree_page);

if (ret < 0) {
put_page(tree_page);
node = node->rb_left;
} else if (ret > 0) {
put_page(tree_page);
node = node->rb_right;
} else
return tree_page;
}

return NULL;
}

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

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

cond_resched();
stable_node = rb_entry(*new, struct stable_node, node);
tree_page = get_ksm_page(stable_node);
if (!tree_page)
return NULL;

ret = memcmp_pages(kpage, tree_page);
put_page(tree_page);

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;
}
}

stable_node = alloc_stable_node();
if (!stable_node)
return NULL;

rb_link_node(&stable_node->node, parent, new);
rb_insert_color(&stable_node->node, &root_stable_tree);

INIT_HLIST_HEAD(&stable_node->hlist);

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

return stable_node;
}

/*
* unstable_tree_search_insert - search for identical page,
* else insert rmap_item into the unstable tree.
*
* 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.
*/
static
struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
struct page *page,
struct page **tree_pagep)

{
struct rb_node **new = &root_unstable_tree.rb_node;
struct rb_node *parent = NULL;

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

cond_resched();
tree_rmap_item = rb_entry(*new, struct rmap_item, node);
tree_page = get_mergeable_page(tree_rmap_item);
if (IS_ERR_OR_NULL(tree_page))
return NULL;

/*
* Don't substitute a ksm page for a forked page.
*/
if (page == tree_page) {
put_page(tree_page);
return NULL;
}

ret = memcmp_pages(page, tree_page);

parent = *new;
if (ret < 0) {
put_page(tree_page);
new = &parent->rb_left;
} else if (ret > 0) {
put_page(tree_page);
new = &parent->rb_right;
} else {
*tree_pagep = tree_page;
return tree_rmap_item;
}
}

rmap_item->address |= UNSTABLE_FLAG;
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);

ksm_pages_unshared++;
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,
struct stable_node *stable_node)
{
rmap_item->head = stable_node;
rmap_item->address |= STABLE_FLAG;
hlist_add_head(&rmap_item->hlist, &stable_node->hlist);

if (rmap_item->hlist.next)
ksm_pages_sharing++;
else
ksm_pages_shared++;
}

/*
* 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.
*
* @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;
struct page *tree_page = NULL;
struct stable_node *stable_node;
struct page *kpage;
unsigned int checksum;
int err;

remove_rmap_item_from_tree(rmap_item);

/* We first start with searching the page inside the stable tree */
kpage = stable_tree_search(page);
if (kpage) {
err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
if (!err) {
/*
* The page was successfully merged:
* add its rmap_item to the stable tree.
*/
lock_page(kpage);
stable_tree_append(rmap_item, page_stable_node(kpage));
unlock_page(kpage);
}
put_page(kpage);
return;
}

/*
* 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.
*/
checksum = calc_checksum(page);
if (rmap_item->oldchecksum != checksum) {
rmap_item->oldchecksum = checksum;
return;
}

tree_rmap_item =
unstable_tree_search_insert(rmap_item, page, &tree_page);
if (tree_rmap_item) {
kpage = try_to_merge_two_pages(rmap_item, page,
tree_rmap_item, tree_page);
put_page(tree_page);
/*
* 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.
*/
if (kpage) {
remove_rmap_item_from_tree(tree_rmap_item);

lock_page(kpage);
stable_node = stable_tree_insert(kpage);
if (stable_node) {
stable_tree_append(tree_rmap_item, stable_node);
stable_tree_append(rmap_item, stable_node);
}
unlock_page(kpage);

/*
* 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.
*/
if (!stable_node) {
break_cow(tree_rmap_item);
break_cow(rmap_item);
}
}
}
}

static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
struct rmap_item **rmap_list,
unsigned long addr)
{
struct rmap_item *rmap_item;

while (*rmap_list) {
rmap_item = *rmap_list;
if ((rmap_item->address & PAGE_MASK) == addr)
return rmap_item;
if (rmap_item->address > addr)
break;
*rmap_list = rmap_item->rmap_list;
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;
rmap_item->rmap_list = *rmap_list;
*rmap_list = rmap_item;
}
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) {
/*
* 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();

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);
/*
* 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;
next_mm:
ksm_scan.address = 0;
ksm_scan.rmap_list = &slot->rmap_list;
}

mm = slot->mm;
down_read(&mm->mmap_sem);
if (ksm_test_exit(mm))
vma = NULL;
else
vma = find_vma(mm, ksm_scan.address);

for (; vma; vma = vma->vm_next) {
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) {
if (ksm_test_exit(mm))
break;
*page = follow_page(vma, ksm_scan.address, FOLL_GET);
if (IS_ERR_OR_NULL(*page)) {
ksm_scan.address += PAGE_SIZE;
cond_resched();
continue;
}
if (PageAnon(*page) ||
page_trans_compound_anon(*page)) {
flush_anon_page(vma, *page, ksm_scan.address);
flush_dcache_page(*page);
rmap_item = get_next_rmap_item(slot,
ksm_scan.rmap_list, ksm_scan.address);
if (rmap_item) {
ksm_scan.rmap_list =
&rmap_item->rmap_list;
ksm_scan.address += PAGE_SIZE;
} else
put_page(*page);
up_read(&mm->mmap_sem);
return rmap_item;
}
put_page(*page);
ksm_scan.address += PAGE_SIZE;
cond_resched();
}
}

if (ksm_test_exit(mm)) {
ksm_scan.address = 0;
ksm_scan.rmap_list = &slot->rmap_list;
}
/*
* Nuke all the rmap_items that are above this current rmap:
* because there were no VM_MERGEABLE vmas with such addresses.
*/
remove_trailing_rmap_items(slot, ksm_scan.rmap_list);

spin_lock(&ksm_mmlist_lock);
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.
* 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).
*/
hlist_del(&slot->link);
list_del(&slot->mm_list);
spin_unlock(&ksm_mmlist_lock);

free_mm_slot(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);
}

/* Repeat until we've completed scanning the whole list */
slot = ksm_scan.mm_slot;
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 *uninitialized_var(page);

while (scan_npages-- && likely(!freezing(current))) {
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);
}
}

static int ksmd_should_run(void)
{
return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
}

static int ksm_scan_thread(void *nothing)
{
set_freezable();
set_user_nice(current, 5);

while (!kthread_should_stop()) {
mutex_lock(&ksm_thread_mutex);
if (ksmd_should_run())
ksm_do_scan(ksm_thread_pages_to_scan);
mutex_unlock(&ksm_thread_mutex);

try_to_freeze();

if (ksmd_should_run()) {
schedule_timeout_interruptible(
msecs_to_jiffies(ksm_thread_sleep_millisecs));
} else {
wait_event_freezable(ksm_thread_wait,
ksmd_should_run() || kthread_should_stop());
}
}
return 0;
}

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;
int err;

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 |
VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
return 0; /* just ignore the advice */

if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
err = __ksm_enter(mm);
if (err)
return err;
}

*vm_flags |= VM_MERGEABLE;
break;

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

if (vma->anon_vma) {
err = unmerge_ksm_pages(vma, start, end);
if (err)
return err;
}

*vm_flags &= ~VM_MERGEABLE;
break;
}

return 0;
}

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

mm_slot = alloc_mm_slot();
if (!mm_slot)
return -ENOMEM;

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

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);

set_bit(MMF_VM_MERGEABLE, &mm->flags);
atomic_inc(&mm->mm_count);

if (needs_wakeup)
wake_up_interruptible(&ksm_thread_wait);

return 0;
}

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

/*
* 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.
*/

spin_lock(&ksm_mmlist_lock);
mm_slot = get_mm_slot(mm);
if (mm_slot && ksm_scan.mm_slot != mm_slot) {
if (!mm_slot->rmap_list) {
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);
}
}
spin_unlock(&ksm_mmlist_lock);

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);
}
}

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;
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 0;
again:
hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
struct anon_vma *anon_vma = rmap_item->anon_vma;
struct anon_vma_chain *vmac;
struct vm_area_struct *vma;

anon_vma_lock(anon_vma);
list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
vma = vmac->vma;
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;

referenced += page_referenced_one(page, vma,
rmap_item->address, &mapcount, vm_flags);
if (!search_new_forks || !mapcount)
break;
}
anon_vma_unlock(anon_vma);
if (!mapcount)
goto out;
}
if (!search_new_forks++)
goto again;
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;
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 SWAP_FAIL;
again:
hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
struct anon_vma *anon_vma = rmap_item->anon_vma;
struct anon_vma_chain *vmac;
struct vm_area_struct *vma;

anon_vma_lock(anon_vma);
list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
vma = vmac->vma;
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)) {
anon_vma_unlock(anon_vma);
goto out;
}
}
anon_vma_unlock(anon_vma);
}
if (!search_new_forks++)
goto again;
out:
return ret;
}

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

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

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

anon_vma_lock(anon_vma);
list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
vma = vmac->vma;
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) {
anon_vma_unlock(anon_vma);
goto out;
}
}
anon_vma_unlock(anon_vma);
}
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) {
VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
stable_node->kpfn = page_to_pfn(newpage);
}
}
#endif /* CONFIG_MIGRATION */

#ifdef CONFIG_MEMORY_HOTREMOVE
static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
unsigned long end_pfn)
{
struct rb_node *node;

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

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

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

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

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

#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,
* breaking COW to free the pages_shared (but leaves 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;
if (flags & KSM_RUN_UNMERGE) {
int oom_score_adj;

oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
err = unmerge_and_remove_all_rmap_items();
test_set_oom_score_adj(oom_score_adj);
if (err) {
ksm_run = KSM_RUN_STOP;
count = err;
}
}
}
mutex_unlock(&ksm_thread_mutex);

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

return count;
}
KSM_ATTR(run);

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)
{
return sprintf(buf, "%lu\n", ksm_pages_sharing);
}
KSM_ATTR_RO(pages_sharing);

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);

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

static struct attribute_group ksm_attr_group = {
.attrs = ksm_attrs,
.name = "ksm",
};
#endif /* CONFIG_SYSFS */

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);
goto out_free;
}

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

#endif /* CONFIG_SYSFS */

#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
return 0;

out_free:
ksm_slab_free();
out:
return err;
}
module_init(ksm_init)
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