linux/mm/ksm.c
Stefan Roesch e5a6899126 mm/ksm: add pages_skipped metric
This change adds the "pages skipped" metric.  To be able to evaluate how
successful smart page scanning is, the pages skipped metric can be
compared to the pages scanned metric.

The pages skipped metric is a cumulative counter.  The counter is stored
under /sys/kernel/mm/ksm/pages_skipped.

Link: https://lkml.kernel.org/r/20230926040939.516161-3-shr@devkernel.io
Signed-off-by: Stefan Roesch <shr@devkernel.io>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-10-16 15:44:39 -07:00

3642 lines
100 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* 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
*/
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/mm_inline.h>
#include <linux/fs.h>
#include <linux/mman.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/sched/coredump.h>
#include <linux/rwsem.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/spinlock.h>
#include <linux/xxhash.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/hashtable.h>
#include <linux/freezer.h>
#include <linux/oom.h>
#include <linux/numa.h>
#include <linux/pagewalk.h>
#include <asm/tlbflush.h>
#include "internal.h"
#include "mm_slot.h"
#define CREATE_TRACE_POINTS
#include <trace/events/ksm.h>
#ifdef CONFIG_NUMA
#define NUMA(x) (x)
#define DO_NUMA(x) do { (x); } while (0)
#else
#define NUMA(x) (0)
#define DO_NUMA(x) do { } while (0)
#endif
typedef u8 rmap_age_t;
/**
* DOC: Overview
*
* 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.
*
* The stable tree node includes information required for reverse
* mapping from a KSM page to virtual addresses that map this page.
*
* In order to avoid large latencies of the rmap walks on KSM pages,
* KSM maintains two types of nodes in the stable tree:
*
* * the regular nodes that keep the reverse mapping structures in a
* linked list
* * the "chains" that link nodes ("dups") that represent the same
* write protected memory content, but each "dup" corresponds to a
* different KSM page copy of that content
*
* Internally, the regular nodes, "dups" and "chains" are represented
* using the same struct ksm_stable_node structure.
*
* 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.)
*
* If the merge_across_nodes tunable is unset, then KSM maintains multiple
* stable trees and multiple unstable trees: one of each for each NUMA node.
*/
/**
* struct ksm_mm_slot - ksm information per mm that is being scanned
* @slot: hash lookup from mm to mm_slot
* @rmap_list: head for this mm_slot's singly-linked list of rmap_items
*/
struct ksm_mm_slot {
struct mm_slot slot;
struct ksm_rmap_item *rmap_list;
};
/**
* 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 ksm_mm_slot *mm_slot;
unsigned long address;
struct ksm_rmap_item **rmap_list;
unsigned long seqnr;
};
/**
* struct ksm_stable_node - node of the stable rbtree
* @node: rb node of this ksm page in the stable tree
* @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
* @hlist_dup: linked into the stable_node->hlist with a stable_node chain
* @list: linked into migrate_nodes, pending placement in the proper node tree
* @hlist: hlist head of rmap_items using this ksm page
* @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
* @chain_prune_time: time of the last full garbage collection
* @rmap_hlist_len: number of rmap_item entries in hlist or STABLE_NODE_CHAIN
* @nid: NUMA node id of stable tree in which linked (may not match kpfn)
*/
struct ksm_stable_node {
union {
struct rb_node node; /* when node of stable tree */
struct { /* when listed for migration */
struct list_head *head;
struct {
struct hlist_node hlist_dup;
struct list_head list;
};
};
};
struct hlist_head hlist;
union {
unsigned long kpfn;
unsigned long chain_prune_time;
};
/*
* STABLE_NODE_CHAIN can be any negative number in
* rmap_hlist_len negative range, but better not -1 to be able
* to reliably detect underflows.
*/
#define STABLE_NODE_CHAIN -1024
int rmap_hlist_len;
#ifdef CONFIG_NUMA
int nid;
#endif
};
/**
* struct ksm_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
* @nid: NUMA node id of unstable tree in which linked (may not match page)
* @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
* @age: number of scan iterations since creation
* @remaining_skips: how many scans to skip
*/
struct ksm_rmap_item {
struct ksm_rmap_item *rmap_list;
union {
struct anon_vma *anon_vma; /* when stable */
#ifdef CONFIG_NUMA
int nid; /* when node of unstable tree */
#endif
};
struct mm_struct *mm;
unsigned long address; /* + low bits used for flags below */
unsigned int oldchecksum; /* when unstable */
rmap_age_t age;
rmap_age_t remaining_skips;
union {
struct rb_node node; /* when node of unstable tree */
struct { /* when listed from stable tree */
struct ksm_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 one_stable_tree[1] = { RB_ROOT };
static struct rb_root one_unstable_tree[1] = { RB_ROOT };
static struct rb_root *root_stable_tree = one_stable_tree;
static struct rb_root *root_unstable_tree = one_unstable_tree;
/* Recently migrated nodes of stable tree, pending proper placement */
static LIST_HEAD(migrate_nodes);
#define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev)
#define MM_SLOTS_HASH_BITS 10
static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
static struct ksm_mm_slot ksm_mm_head = {
.slot.mm_node = LIST_HEAD_INIT(ksm_mm_head.slot.mm_node),
};
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 pages scanned */
static unsigned long ksm_pages_scanned;
/* 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;
/* The number of stable_node chains */
static unsigned long ksm_stable_node_chains;
/* The number of stable_node dups linked to the stable_node chains */
static unsigned long ksm_stable_node_dups;
/* Delay in pruning stale stable_node_dups in the stable_node_chains */
static unsigned int ksm_stable_node_chains_prune_millisecs = 2000;
/* Maximum number of page slots sharing a stable node */
static int ksm_max_page_sharing = 256;
/* 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;
/* Checksum of an empty (zeroed) page */
static unsigned int zero_checksum __read_mostly;
/* Whether to merge empty (zeroed) pages with actual zero pages */
static bool ksm_use_zero_pages __read_mostly;
/* Skip pages that couldn't be de-duplicated previously */
/* Default to true at least temporarily, for testing */
static bool ksm_smart_scan = true;
/* The number of zero pages which is placed by KSM */
unsigned long ksm_zero_pages;
/* The number of pages that have been skipped due to "smart scanning" */
static unsigned long ksm_pages_skipped;
#ifdef CONFIG_NUMA
/* Zeroed when merging across nodes is not allowed */
static unsigned int ksm_merge_across_nodes = 1;
static int ksm_nr_node_ids = 1;
#else
#define ksm_merge_across_nodes 1U
#define ksm_nr_node_ids 1
#endif
#define KSM_RUN_STOP 0
#define KSM_RUN_MERGE 1
#define KSM_RUN_UNMERGE 2
#define KSM_RUN_OFFLINE 4
static unsigned long ksm_run = KSM_RUN_STOP;
static void wait_while_offlining(void);
static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait);
static DEFINE_MUTEX(ksm_thread_mutex);
static DEFINE_SPINLOCK(ksm_mmlist_lock);
#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create(#__struct,\
sizeof(struct __struct), __alignof__(struct __struct),\
(__flags), NULL)
static int __init ksm_slab_init(void)
{
rmap_item_cache = KSM_KMEM_CACHE(ksm_rmap_item, 0);
if (!rmap_item_cache)
goto out;
stable_node_cache = KSM_KMEM_CACHE(ksm_stable_node, 0);
if (!stable_node_cache)
goto out_free1;
mm_slot_cache = KSM_KMEM_CACHE(ksm_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 __always_inline bool is_stable_node_chain(struct ksm_stable_node *chain)
{
return chain->rmap_hlist_len == STABLE_NODE_CHAIN;
}
static __always_inline bool is_stable_node_dup(struct ksm_stable_node *dup)
{
return dup->head == STABLE_NODE_DUP_HEAD;
}
static inline void stable_node_chain_add_dup(struct ksm_stable_node *dup,
struct ksm_stable_node *chain)
{
VM_BUG_ON(is_stable_node_dup(dup));
dup->head = STABLE_NODE_DUP_HEAD;
VM_BUG_ON(!is_stable_node_chain(chain));
hlist_add_head(&dup->hlist_dup, &chain->hlist);
ksm_stable_node_dups++;
}
static inline void __stable_node_dup_del(struct ksm_stable_node *dup)
{
VM_BUG_ON(!is_stable_node_dup(dup));
hlist_del(&dup->hlist_dup);
ksm_stable_node_dups--;
}
static inline void stable_node_dup_del(struct ksm_stable_node *dup)
{
VM_BUG_ON(is_stable_node_chain(dup));
if (is_stable_node_dup(dup))
__stable_node_dup_del(dup);
else
rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid));
#ifdef CONFIG_DEBUG_VM
dup->head = NULL;
#endif
}
static inline struct ksm_rmap_item *alloc_rmap_item(void)
{
struct ksm_rmap_item *rmap_item;
rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL |
__GFP_NORETRY | __GFP_NOWARN);
if (rmap_item)
ksm_rmap_items++;
return rmap_item;
}
static inline void free_rmap_item(struct ksm_rmap_item *rmap_item)
{
ksm_rmap_items--;
rmap_item->mm->ksm_rmap_items--;
rmap_item->mm = NULL; /* debug safety */
kmem_cache_free(rmap_item_cache, rmap_item);
}
static inline struct ksm_stable_node *alloc_stable_node(void)
{
/*
* The allocation can take too long with GFP_KERNEL when memory is under
* pressure, which may lead to hung task warnings. Adding __GFP_HIGH
* grants access to memory reserves, helping to avoid this problem.
*/
return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH);
}
static inline void free_stable_node(struct ksm_stable_node *stable_node)
{
VM_BUG_ON(stable_node->rmap_hlist_len &&
!is_stable_node_chain(stable_node));
kmem_cache_free(stable_node_cache, stable_node);
}
/*
* 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_lock 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;
}
static int break_ksm_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long next,
struct mm_walk *walk)
{
struct page *page = NULL;
spinlock_t *ptl;
pte_t *pte;
pte_t ptent;
int ret;
pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
if (!pte)
return 0;
ptent = ptep_get(pte);
if (pte_present(ptent)) {
page = vm_normal_page(walk->vma, addr, ptent);
} else if (!pte_none(ptent)) {
swp_entry_t entry = pte_to_swp_entry(ptent);
/*
* As KSM pages remain KSM pages until freed, no need to wait
* here for migration to end.
*/
if (is_migration_entry(entry))
page = pfn_swap_entry_to_page(entry);
}
/* return 1 if the page is an normal ksm page or KSM-placed zero page */
ret = (page && PageKsm(page)) || is_ksm_zero_pte(*pte);
pte_unmap_unlock(pte, ptl);
return ret;
}
static const struct mm_walk_ops break_ksm_ops = {
.pmd_entry = break_ksm_pmd_entry,
.walk_lock = PGWALK_RDLOCK,
};
static const struct mm_walk_ops break_ksm_lock_vma_ops = {
.pmd_entry = break_ksm_pmd_entry,
.walk_lock = PGWALK_WRLOCK,
};
/*
* We use break_ksm to break COW on a ksm page by triggering unsharing,
* such that the ksm page will get replaced by an exclusive anonymous page.
*
* We take 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, where we would not want to touch it.
*
* FAULT_FLAG_REMOTE/FOLL_REMOTE are because we do this outside the context
* of the process that owns 'vma'. We also do not want to enforce
* protection keys here anyway.
*/
static int break_ksm(struct vm_area_struct *vma, unsigned long addr, bool lock_vma)
{
vm_fault_t ret = 0;
const struct mm_walk_ops *ops = lock_vma ?
&break_ksm_lock_vma_ops : &break_ksm_ops;
do {
int ksm_page;
cond_resched();
ksm_page = walk_page_range_vma(vma, addr, addr + 1, ops, NULL);
if (WARN_ON_ONCE(ksm_page < 0))
return ksm_page;
if (!ksm_page)
return 0;
ret = handle_mm_fault(vma, addr,
FAULT_FLAG_UNSHARE | FAULT_FLAG_REMOTE,
NULL);
} while (!(ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
/*
* We must loop until we no longer find a KSM page because
* handle_mm_fault() may back out if there's any difficulty e.g. if
* pte accessed bit gets updated concurrently.
*
* 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 bool vma_ksm_compatible(struct vm_area_struct *vma)
{
if (vma->vm_flags & (VM_SHARED | VM_MAYSHARE | VM_PFNMAP |
VM_IO | VM_DONTEXPAND | VM_HUGETLB |
VM_MIXEDMAP))
return false; /* just ignore the advice */
if (vma_is_dax(vma))
return false;
#ifdef VM_SAO
if (vma->vm_flags & VM_SAO)
return false;
#endif
#ifdef VM_SPARC_ADI
if (vma->vm_flags & VM_SPARC_ADI)
return false;
#endif
return true;
}
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 = vma_lookup(mm, addr);
if (!vma || !(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
return NULL;
return vma;
}
static void break_cow(struct ksm_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);
mmap_read_lock(mm);
vma = find_mergeable_vma(mm, addr);
if (vma)
break_ksm(vma, addr, false);
mmap_read_unlock(mm);
}
static struct page *get_mergeable_page(struct ksm_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;
mmap_read_lock(mm);
vma = find_mergeable_vma(mm, addr);
if (!vma)
goto out;
page = follow_page(vma, addr, FOLL_GET);
if (IS_ERR_OR_NULL(page))
goto out;
if (is_zone_device_page(page))
goto out_putpage;
if (PageAnon(page)) {
flush_anon_page(vma, page, addr);
flush_dcache_page(page);
} else {
out_putpage:
put_page(page);
out:
page = NULL;
}
mmap_read_unlock(mm);
return page;
}
/*
* This helper is used for getting right index into array of tree roots.
* When merge_across_nodes knob is set to 1, there are only two rb-trees for
* stable and unstable pages from all nodes with roots in index 0. Otherwise,
* every node has its own stable and unstable tree.
*/
static inline int get_kpfn_nid(unsigned long kpfn)
{
return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
}
static struct ksm_stable_node *alloc_stable_node_chain(struct ksm_stable_node *dup,
struct rb_root *root)
{
struct ksm_stable_node *chain = alloc_stable_node();
VM_BUG_ON(is_stable_node_chain(dup));
if (likely(chain)) {
INIT_HLIST_HEAD(&chain->hlist);
chain->chain_prune_time = jiffies;
chain->rmap_hlist_len = STABLE_NODE_CHAIN;
#if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA)
chain->nid = NUMA_NO_NODE; /* debug */
#endif
ksm_stable_node_chains++;
/*
* Put the stable node chain in the first dimension of
* the stable tree and at the same time remove the old
* stable node.
*/
rb_replace_node(&dup->node, &chain->node, root);
/*
* Move the old stable node to the second dimension
* queued in the hlist_dup. The invariant is that all
* dup stable_nodes in the chain->hlist point to pages
* that are write protected and have the exact same
* content.
*/
stable_node_chain_add_dup(dup, chain);
}
return chain;
}
static inline void free_stable_node_chain(struct ksm_stable_node *chain,
struct rb_root *root)
{
rb_erase(&chain->node, root);
free_stable_node(chain);
ksm_stable_node_chains--;
}
static void remove_node_from_stable_tree(struct ksm_stable_node *stable_node)
{
struct ksm_rmap_item *rmap_item;
/* check it's not STABLE_NODE_CHAIN or negative */
BUG_ON(stable_node->rmap_hlist_len < 0);
hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
if (rmap_item->hlist.next) {
ksm_pages_sharing--;
trace_ksm_remove_rmap_item(stable_node->kpfn, rmap_item, rmap_item->mm);
} else {
ksm_pages_shared--;
}
rmap_item->mm->ksm_merging_pages--;
VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
stable_node->rmap_hlist_len--;
put_anon_vma(rmap_item->anon_vma);
rmap_item->address &= PAGE_MASK;
cond_resched();
}
/*
* We need the second aligned pointer of the migrate_nodes
* list_head to stay clear from the rb_parent_color union
* (aligned and different than any node) and also different
* from &migrate_nodes. This will verify that future list.h changes
* don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it.
*/
BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes);
BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1);
trace_ksm_remove_ksm_page(stable_node->kpfn);
if (stable_node->head == &migrate_nodes)
list_del(&stable_node->list);
else
stable_node_dup_del(stable_node);
free_stable_node(stable_node);
}
enum get_ksm_page_flags {
GET_KSM_PAGE_NOLOCK,
GET_KSM_PAGE_LOCK,
GET_KSM_PAGE_TRYLOCK
};
/*
* 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.
* But beware, the stable node's page might be being migrated.
*
* 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.
* is on its way to being freed; but it is an anomaly to bear in mind.
*/
static struct page *get_ksm_page(struct ksm_stable_node *stable_node,
enum get_ksm_page_flags flags)
{
struct page *page;
void *expected_mapping;
unsigned long kpfn;
expected_mapping = (void *)((unsigned long)stable_node |
PAGE_MAPPING_KSM);
again:
kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */
page = pfn_to_page(kpfn);
if (READ_ONCE(page->mapping) != expected_mapping)
goto stale;
/*
* We cannot do anything with the page while its refcount is 0.
* Usually 0 means free, or tail of a higher-order page: in which
* case this node is no longer referenced, and should be freed;
* however, it might mean that the page is under page_ref_freeze().
* The __remove_mapping() case is easy, again the node is now stale;
* the same is in reuse_ksm_page() case; but if page is swapcache
* in folio_migrate_mapping(), it might still be our page,
* in which case it's essential to keep the node.
*/
while (!get_page_unless_zero(page)) {
/*
* Another check for page->mapping != expected_mapping would
* work here too. We have chosen the !PageSwapCache test to
* optimize the common case, when the page is or is about to
* be freed: PageSwapCache is cleared (under spin_lock_irq)
* in the ref_freeze section of __remove_mapping(); but Anon
* page->mapping reset to NULL later, in free_pages_prepare().
*/
if (!PageSwapCache(page))
goto stale;
cpu_relax();
}
if (READ_ONCE(page->mapping) != expected_mapping) {
put_page(page);
goto stale;
}
if (flags == GET_KSM_PAGE_TRYLOCK) {
if (!trylock_page(page)) {
put_page(page);
return ERR_PTR(-EBUSY);
}
} else if (flags == GET_KSM_PAGE_LOCK)
lock_page(page);
if (flags != GET_KSM_PAGE_NOLOCK) {
if (READ_ONCE(page->mapping) != expected_mapping) {
unlock_page(page);
put_page(page);
goto stale;
}
}
return page;
stale:
/*
* We come here from above when page->mapping or !PageSwapCache
* suggests that the node is stale; but it might be under migration.
* We need smp_rmb(), matching the smp_wmb() in folio_migrate_ksm(),
* before checking whether node->kpfn has been changed.
*/
smp_rmb();
if (READ_ONCE(stable_node->kpfn) != kpfn)
goto again;
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 ksm_rmap_item *rmap_item)
{
if (rmap_item->address & STABLE_FLAG) {
struct ksm_stable_node *stable_node;
struct page *page;
stable_node = rmap_item->head;
page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
if (!page)
goto out;
hlist_del(&rmap_item->hlist);
unlock_page(page);
put_page(page);
if (!hlist_empty(&stable_node->hlist))
ksm_pages_sharing--;
else
ksm_pages_shared--;
rmap_item->mm->ksm_merging_pages--;
VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
stable_node->rmap_hlist_len--;
put_anon_vma(rmap_item->anon_vma);
rmap_item->head = NULL;
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 + NUMA(rmap_item->nid));
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 ksm_rmap_item **rmap_list)
{
while (*rmap_list) {
struct ksm_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 rmap_items from stable tree 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_lock. 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, bool lock_vma)
{
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, lock_vma);
}
return err;
}
static inline struct ksm_stable_node *folio_stable_node(struct folio *folio)
{
return folio_test_ksm(folio) ? folio_raw_mapping(folio) : NULL;
}
static inline struct ksm_stable_node *page_stable_node(struct page *page)
{
return folio_stable_node(page_folio(page));
}
static inline void set_page_stable_node(struct page *page,
struct ksm_stable_node *stable_node)
{
VM_BUG_ON_PAGE(PageAnon(page) && PageAnonExclusive(page), page);
page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM);
}
#ifdef CONFIG_SYSFS
/*
* Only called through the sysfs control interface:
*/
static int remove_stable_node(struct ksm_stable_node *stable_node)
{
struct page *page;
int err;
page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
if (!page) {
/*
* get_ksm_page did remove_node_from_stable_tree itself.
*/
return 0;
}
/*
* Page could be still mapped if this races with __mmput() running in
* between ksm_exit() and exit_mmap(). Just refuse to let
* merge_across_nodes/max_page_sharing be switched.
*/
err = -EBUSY;
if (!page_mapped(page)) {
/*
* The stable node did not yet appear stale to get_ksm_page(),
* since that allows for an unmapped ksm page to be recognized
* right up until it is freed; but the node is safe to remove.
* This page might be in an LRU cache waiting to be freed,
* or it might be PageSwapCache (perhaps under writeback),
* or it might have been removed from swapcache a moment ago.
*/
set_page_stable_node(page, NULL);
remove_node_from_stable_tree(stable_node);
err = 0;
}
unlock_page(page);
put_page(page);
return err;
}
static int remove_stable_node_chain(struct ksm_stable_node *stable_node,
struct rb_root *root)
{
struct ksm_stable_node *dup;
struct hlist_node *hlist_safe;
if (!is_stable_node_chain(stable_node)) {
VM_BUG_ON(is_stable_node_dup(stable_node));
if (remove_stable_node(stable_node))
return true;
else
return false;
}
hlist_for_each_entry_safe(dup, hlist_safe,
&stable_node->hlist, hlist_dup) {
VM_BUG_ON(!is_stable_node_dup(dup));
if (remove_stable_node(dup))
return true;
}
BUG_ON(!hlist_empty(&stable_node->hlist));
free_stable_node_chain(stable_node, root);
return false;
}
static int remove_all_stable_nodes(void)
{
struct ksm_stable_node *stable_node, *next;
int nid;
int err = 0;
for (nid = 0; nid < ksm_nr_node_ids; nid++) {
while (root_stable_tree[nid].rb_node) {
stable_node = rb_entry(root_stable_tree[nid].rb_node,
struct ksm_stable_node, node);
if (remove_stable_node_chain(stable_node,
root_stable_tree + nid)) {
err = -EBUSY;
break; /* proceed to next nid */
}
cond_resched();
}
}
list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
if (remove_stable_node(stable_node))
err = -EBUSY;
cond_resched();
}
return err;
}
static int unmerge_and_remove_all_rmap_items(void)
{
struct ksm_mm_slot *mm_slot;
struct mm_slot *slot;
struct mm_struct *mm;
struct vm_area_struct *vma;
int err = 0;
spin_lock(&ksm_mmlist_lock);
slot = list_entry(ksm_mm_head.slot.mm_node.next,
struct mm_slot, mm_node);
ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
spin_unlock(&ksm_mmlist_lock);
for (mm_slot = ksm_scan.mm_slot; mm_slot != &ksm_mm_head;
mm_slot = ksm_scan.mm_slot) {
VMA_ITERATOR(vmi, mm_slot->slot.mm, 0);
mm = mm_slot->slot.mm;
mmap_read_lock(mm);
/*
* Exit right away if mm is exiting to avoid lockdep issue in
* the maple tree
*/
if (ksm_test_exit(mm))
goto mm_exiting;
for_each_vma(vmi, vma) {
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
continue;
err = unmerge_ksm_pages(vma,
vma->vm_start, vma->vm_end, false);
if (err)
goto error;
}
mm_exiting:
remove_trailing_rmap_items(&mm_slot->rmap_list);
mmap_read_unlock(mm);
spin_lock(&ksm_mmlist_lock);
slot = list_entry(mm_slot->slot.mm_node.next,
struct mm_slot, mm_node);
ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
if (ksm_test_exit(mm)) {
hash_del(&mm_slot->slot.hash);
list_del(&mm_slot->slot.mm_node);
spin_unlock(&ksm_mmlist_lock);
mm_slot_free(mm_slot_cache, mm_slot);
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
mmdrop(mm);
} else
spin_unlock(&ksm_mmlist_lock);
}
/* Clean up stable nodes, but don't worry if some are still busy */
remove_all_stable_nodes();
ksm_scan.seqnr = 0;
return 0;
error:
mmap_read_unlock(mm);
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);
checksum = xxhash(addr, PAGE_SIZE, 0);
kunmap_atomic(addr);
return checksum;
}
static int write_protect_page(struct vm_area_struct *vma, struct page *page,
pte_t *orig_pte)
{
struct mm_struct *mm = vma->vm_mm;
DEFINE_PAGE_VMA_WALK(pvmw, page, vma, 0, 0);
int swapped;
int err = -EFAULT;
struct mmu_notifier_range range;
bool anon_exclusive;
pte_t entry;
pvmw.address = page_address_in_vma(page, vma);
if (pvmw.address == -EFAULT)
goto out;
BUG_ON(PageTransCompound(page));
mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, pvmw.address,
pvmw.address + PAGE_SIZE);
mmu_notifier_invalidate_range_start(&range);
if (!page_vma_mapped_walk(&pvmw))
goto out_mn;
if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?"))
goto out_unlock;
anon_exclusive = PageAnonExclusive(page);
entry = ptep_get(pvmw.pte);
if (pte_write(entry) || pte_dirty(entry) ||
anon_exclusive || mm_tlb_flush_pending(mm)) {
swapped = PageSwapCache(page);
flush_cache_page(vma, pvmw.address, 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 racy 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.
*
* No need to notify as we are downgrading page table to read
* only not changing it to point to a new page.
*
* See Documentation/mm/mmu_notifier.rst
*/
entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte);
/*
* 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, pvmw.address, pvmw.pte, entry);
goto out_unlock;
}
/* See page_try_share_anon_rmap(): clear PTE first. */
if (anon_exclusive && page_try_share_anon_rmap(page)) {
set_pte_at(mm, pvmw.address, pvmw.pte, entry);
goto out_unlock;
}
if (pte_dirty(entry))
set_page_dirty(page);
entry = pte_mkclean(entry);
if (pte_write(entry))
entry = pte_wrprotect(entry);
set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry);
}
*orig_pte = entry;
err = 0;
out_unlock:
page_vma_mapped_walk_done(&pvmw);
out_mn:
mmu_notifier_invalidate_range_end(&range);
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;
struct folio *folio;
pmd_t *pmd;
pmd_t pmde;
pte_t *ptep;
pte_t newpte;
spinlock_t *ptl;
unsigned long addr;
int err = -EFAULT;
struct mmu_notifier_range range;
addr = page_address_in_vma(page, vma);
if (addr == -EFAULT)
goto out;
pmd = mm_find_pmd(mm, addr);
if (!pmd)
goto out;
/*
* Some THP functions use the sequence pmdp_huge_clear_flush(), set_pmd_at()
* without holding anon_vma lock for write. So when looking for a
* genuine pmde (in which to find pte), test present and !THP together.
*/
pmde = pmdp_get_lockless(pmd);
if (!pmd_present(pmde) || pmd_trans_huge(pmde))
goto out;
mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, addr,
addr + PAGE_SIZE);
mmu_notifier_invalidate_range_start(&range);
ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
if (!ptep)
goto out_mn;
if (!pte_same(ptep_get(ptep), orig_pte)) {
pte_unmap_unlock(ptep, ptl);
goto out_mn;
}
VM_BUG_ON_PAGE(PageAnonExclusive(page), page);
VM_BUG_ON_PAGE(PageAnon(kpage) && PageAnonExclusive(kpage), kpage);
/*
* No need to check ksm_use_zero_pages here: we can only have a
* zero_page here if ksm_use_zero_pages was enabled already.
*/
if (!is_zero_pfn(page_to_pfn(kpage))) {
get_page(kpage);
page_add_anon_rmap(kpage, vma, addr, RMAP_NONE);
newpte = mk_pte(kpage, vma->vm_page_prot);
} else {
/*
* Use pte_mkdirty to mark the zero page mapped by KSM, and then
* we can easily track all KSM-placed zero pages by checking if
* the dirty bit in zero page's PTE is set.
*/
newpte = pte_mkdirty(pte_mkspecial(pfn_pte(page_to_pfn(kpage), vma->vm_page_prot)));
ksm_zero_pages++;
mm->ksm_zero_pages++;
/*
* We're replacing an anonymous page with a zero page, which is
* not anonymous. We need to do proper accounting otherwise we
* will get wrong values in /proc, and a BUG message in dmesg
* when tearing down the mm.
*/
dec_mm_counter(mm, MM_ANONPAGES);
}
flush_cache_page(vma, addr, pte_pfn(ptep_get(ptep)));
/*
* No need to notify as we are replacing a read only page with another
* read only page with the same content.
*
* See Documentation/mm/mmu_notifier.rst
*/
ptep_clear_flush(vma, addr, ptep);
set_pte_at_notify(mm, addr, ptep, newpte);
folio = page_folio(page);
page_remove_rmap(page, vma, false);
if (!folio_mapped(folio))
folio_free_swap(folio);
folio_put(folio);
pte_unmap_unlock(ptep, ptl);
err = 0;
out_mn:
mmu_notifier_invalidate_range_end(&range);
out:
return err;
}
/*
* 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 (!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 (PageTransCompound(page)) {
if (split_huge_page(page))
goto out_unlock;
}
/*
* 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);
/*
* Page reclaim just frees a clean page with no dirty
* ptes: make sure that the ksm page would be swapped.
*/
if (!PageDirty(page))
SetPageDirty(page);
err = 0;
} else if (pages_identical(page, kpage))
err = replace_page(vma, page, kpage, orig_pte);
}
out_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 ksm_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;
mmap_read_lock(mm);
vma = find_mergeable_vma(mm, rmap_item->address);
if (!vma)
goto out;
err = try_to_merge_one_page(vma, page, kpage);
if (err)
goto out;
/* Unstable nid is in union with stable anon_vma: remove first */
remove_rmap_item_from_tree(rmap_item);
/* Must get reference to anon_vma while still holding mmap_lock */
rmap_item->anon_vma = vma->anon_vma;
get_anon_vma(vma->anon_vma);
out:
mmap_read_unlock(mm);
trace_ksm_merge_with_ksm_page(kpage, page_to_pfn(kpage ? kpage : page),
rmap_item, mm, err);
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 ksm_rmap_item *rmap_item,
struct page *page,
struct ksm_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;
}
static __always_inline
bool __is_page_sharing_candidate(struct ksm_stable_node *stable_node, int offset)
{
VM_BUG_ON(stable_node->rmap_hlist_len < 0);
/*
* Check that at least one mapping still exists, otherwise
* there's no much point to merge and share with this
* stable_node, as the underlying tree_page of the other
* sharer is going to be freed soon.
*/
return stable_node->rmap_hlist_len &&
stable_node->rmap_hlist_len + offset < ksm_max_page_sharing;
}
static __always_inline
bool is_page_sharing_candidate(struct ksm_stable_node *stable_node)
{
return __is_page_sharing_candidate(stable_node, 0);
}
static struct page *stable_node_dup(struct ksm_stable_node **_stable_node_dup,
struct ksm_stable_node **_stable_node,
struct rb_root *root,
bool prune_stale_stable_nodes)
{
struct ksm_stable_node *dup, *found = NULL, *stable_node = *_stable_node;
struct hlist_node *hlist_safe;
struct page *_tree_page, *tree_page = NULL;
int nr = 0;
int found_rmap_hlist_len;
if (!prune_stale_stable_nodes ||
time_before(jiffies, stable_node->chain_prune_time +
msecs_to_jiffies(
ksm_stable_node_chains_prune_millisecs)))
prune_stale_stable_nodes = false;
else
stable_node->chain_prune_time = jiffies;
hlist_for_each_entry_safe(dup, hlist_safe,
&stable_node->hlist, hlist_dup) {
cond_resched();
/*
* We must walk all stable_node_dup to prune the stale
* stable nodes during lookup.
*
* get_ksm_page can drop the nodes from the
* stable_node->hlist if they point to freed pages
* (that's why we do a _safe walk). The "dup"
* stable_node parameter itself will be freed from
* under us if it returns NULL.
*/
_tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK);
if (!_tree_page)
continue;
nr += 1;
if (is_page_sharing_candidate(dup)) {
if (!found ||
dup->rmap_hlist_len > found_rmap_hlist_len) {
if (found)
put_page(tree_page);
found = dup;
found_rmap_hlist_len = found->rmap_hlist_len;
tree_page = _tree_page;
/* skip put_page for found dup */
if (!prune_stale_stable_nodes)
break;
continue;
}
}
put_page(_tree_page);
}
if (found) {
/*
* nr is counting all dups in the chain only if
* prune_stale_stable_nodes is true, otherwise we may
* break the loop at nr == 1 even if there are
* multiple entries.
*/
if (prune_stale_stable_nodes && nr == 1) {
/*
* If there's not just one entry it would
* corrupt memory, better BUG_ON. In KSM
* context with no lock held it's not even
* fatal.
*/
BUG_ON(stable_node->hlist.first->next);
/*
* There's just one entry and it is below the
* deduplication limit so drop the chain.
*/
rb_replace_node(&stable_node->node, &found->node,
root);
free_stable_node(stable_node);
ksm_stable_node_chains--;
ksm_stable_node_dups--;
/*
* NOTE: the caller depends on the stable_node
* to be equal to stable_node_dup if the chain
* was collapsed.
*/
*_stable_node = found;
/*
* Just for robustness, as stable_node is
* otherwise left as a stable pointer, the
* compiler shall optimize it away at build
* time.
*/
stable_node = NULL;
} else if (stable_node->hlist.first != &found->hlist_dup &&
__is_page_sharing_candidate(found, 1)) {
/*
* If the found stable_node dup can accept one
* more future merge (in addition to the one
* that is underway) and is not at the head of
* the chain, put it there so next search will
* be quicker in the !prune_stale_stable_nodes
* case.
*
* NOTE: it would be inaccurate to use nr > 1
* instead of checking the hlist.first pointer
* directly, because in the
* prune_stale_stable_nodes case "nr" isn't
* the position of the found dup in the chain,
* but the total number of dups in the chain.
*/
hlist_del(&found->hlist_dup);
hlist_add_head(&found->hlist_dup,
&stable_node->hlist);
}
}
*_stable_node_dup = found;
return tree_page;
}
static struct ksm_stable_node *stable_node_dup_any(struct ksm_stable_node *stable_node,
struct rb_root *root)
{
if (!is_stable_node_chain(stable_node))
return stable_node;
if (hlist_empty(&stable_node->hlist)) {
free_stable_node_chain(stable_node, root);
return NULL;
}
return hlist_entry(stable_node->hlist.first,
typeof(*stable_node), hlist_dup);
}
/*
* Like for get_ksm_page, this function can free the *_stable_node and
* *_stable_node_dup if the returned tree_page is NULL.
*
* It can also free and overwrite *_stable_node with the found
* stable_node_dup if the chain is collapsed (in which case
* *_stable_node will be equal to *_stable_node_dup like if the chain
* never existed). It's up to the caller to verify tree_page is not
* NULL before dereferencing *_stable_node or *_stable_node_dup.
*
* *_stable_node_dup is really a second output parameter of this
* function and will be overwritten in all cases, the caller doesn't
* need to initialize it.
*/
static struct page *__stable_node_chain(struct ksm_stable_node **_stable_node_dup,
struct ksm_stable_node **_stable_node,
struct rb_root *root,
bool prune_stale_stable_nodes)
{
struct ksm_stable_node *stable_node = *_stable_node;
if (!is_stable_node_chain(stable_node)) {
if (is_page_sharing_candidate(stable_node)) {
*_stable_node_dup = stable_node;
return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK);
}
/*
* _stable_node_dup set to NULL means the stable_node
* reached the ksm_max_page_sharing limit.
*/
*_stable_node_dup = NULL;
return NULL;
}
return stable_node_dup(_stable_node_dup, _stable_node, root,
prune_stale_stable_nodes);
}
static __always_inline struct page *chain_prune(struct ksm_stable_node **s_n_d,
struct ksm_stable_node **s_n,
struct rb_root *root)
{
return __stable_node_chain(s_n_d, s_n, root, true);
}
static __always_inline struct page *chain(struct ksm_stable_node **s_n_d,
struct ksm_stable_node *s_n,
struct rb_root *root)
{
struct ksm_stable_node *old_stable_node = s_n;
struct page *tree_page;
tree_page = __stable_node_chain(s_n_d, &s_n, root, false);
/* not pruning dups so s_n cannot have changed */
VM_BUG_ON(s_n != old_stable_node);
return tree_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)
{
int nid;
struct rb_root *root;
struct rb_node **new;
struct rb_node *parent;
struct ksm_stable_node *stable_node, *stable_node_dup, *stable_node_any;
struct ksm_stable_node *page_node;
page_node = page_stable_node(page);
if (page_node && page_node->head != &migrate_nodes) {
/* ksm page forked */
get_page(page);
return page;
}
nid = get_kpfn_nid(page_to_pfn(page));
root = root_stable_tree + nid;
again:
new = &root->rb_node;
parent = NULL;
while (*new) {
struct page *tree_page;
int ret;
cond_resched();
stable_node = rb_entry(*new, struct ksm_stable_node, node);
stable_node_any = NULL;
tree_page = chain_prune(&stable_node_dup, &stable_node, root);
/*
* NOTE: stable_node may have been freed by
* chain_prune() if the returned stable_node_dup is
* not NULL. stable_node_dup may have been inserted in
* the rbtree instead as a regular stable_node (in
* order to collapse the stable_node chain if a single
* stable_node dup was found in it). In such case the
* stable_node is overwritten by the callee to point
* to the stable_node_dup that was collapsed in the
* stable rbtree and stable_node will be equal to
* stable_node_dup like if the chain never existed.
*/
if (!stable_node_dup) {
/*
* Either all stable_node dups were full in
* this stable_node chain, or this chain was
* empty and should be rb_erased.
*/
stable_node_any = stable_node_dup_any(stable_node,
root);
if (!stable_node_any) {
/* rb_erase just run */
goto again;
}
/*
* Take any of the stable_node dups page of
* this stable_node chain to let the tree walk
* continue. All KSM pages belonging to the
* stable_node dups in a stable_node chain
* have the same content and they're
* write protected at all times. Any will work
* fine to continue the walk.
*/
tree_page = get_ksm_page(stable_node_any,
GET_KSM_PAGE_NOLOCK);
}
VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
if (!tree_page) {
/*
* If we walked over a stale stable_node,
* get_ksm_page() will call rb_erase() and it
* may rebalance the tree from under us. So
* restart the search from scratch. Returning
* NULL would be safe too, but we'd generate
* false negative insertions just because some
* stable_node was stale.
*/
goto again;
}
ret = memcmp_pages(page, tree_page);
put_page(tree_page);
parent = *new;
if (ret < 0)
new = &parent->rb_left;
else if (ret > 0)
new = &parent->rb_right;
else {
if (page_node) {
VM_BUG_ON(page_node->head != &migrate_nodes);
/*
* Test if the migrated page should be merged
* into a stable node dup. If the mapcount is
* 1 we can migrate it with another KSM page
* without adding it to the chain.
*/
if (page_mapcount(page) > 1)
goto chain_append;
}
if (!stable_node_dup) {
/*
* If the stable_node is a chain and
* we got a payload match in memcmp
* but we cannot merge the scanned
* page in any of the existing
* stable_node dups because they're
* all full, we need to wait the
* scanned page to find itself a match
* in the unstable tree to create a
* brand new KSM page to add later to
* the dups of this stable_node.
*/
return NULL;
}
/*
* Lock and unlock the stable_node's page (which
* might already have been migrated) so that page
* migration is sure to notice its raised count.
* It would be more elegant to return stable_node
* than kpage, but that involves more changes.
*/
tree_page = get_ksm_page(stable_node_dup,
GET_KSM_PAGE_TRYLOCK);
if (PTR_ERR(tree_page) == -EBUSY)
return ERR_PTR(-EBUSY);
if (unlikely(!tree_page))
/*
* The tree may have been rebalanced,
* so re-evaluate parent and new.
*/
goto again;
unlock_page(tree_page);
if (get_kpfn_nid(stable_node_dup->kpfn) !=
NUMA(stable_node_dup->nid)) {
put_page(tree_page);
goto replace;
}
return tree_page;
}
}
if (!page_node)
return NULL;
list_del(&page_node->list);
DO_NUMA(page_node->nid = nid);
rb_link_node(&page_node->node, parent, new);
rb_insert_color(&page_node->node, root);
out:
if (is_page_sharing_candidate(page_node)) {
get_page(page);
return page;
} else
return NULL;
replace:
/*
* If stable_node was a chain and chain_prune collapsed it,
* stable_node has been updated to be the new regular
* stable_node. A collapse of the chain is indistinguishable
* from the case there was no chain in the stable
* rbtree. Otherwise stable_node is the chain and
* stable_node_dup is the dup to replace.
*/
if (stable_node_dup == stable_node) {
VM_BUG_ON(is_stable_node_chain(stable_node_dup));
VM_BUG_ON(is_stable_node_dup(stable_node_dup));
/* there is no chain */
if (page_node) {
VM_BUG_ON(page_node->head != &migrate_nodes);
list_del(&page_node->list);
DO_NUMA(page_node->nid = nid);
rb_replace_node(&stable_node_dup->node,
&page_node->node,
root);
if (is_page_sharing_candidate(page_node))
get_page(page);
else
page = NULL;
} else {
rb_erase(&stable_node_dup->node, root);
page = NULL;
}
} else {
VM_BUG_ON(!is_stable_node_chain(stable_node));
__stable_node_dup_del(stable_node_dup);
if (page_node) {
VM_BUG_ON(page_node->head != &migrate_nodes);
list_del(&page_node->list);
DO_NUMA(page_node->nid = nid);
stable_node_chain_add_dup(page_node, stable_node);
if (is_page_sharing_candidate(page_node))
get_page(page);
else
page = NULL;
} else {
page = NULL;
}
}
stable_node_dup->head = &migrate_nodes;
list_add(&stable_node_dup->list, stable_node_dup->head);
return page;
chain_append:
/* stable_node_dup could be null if it reached the limit */
if (!stable_node_dup)
stable_node_dup = stable_node_any;
/*
* If stable_node was a chain and chain_prune collapsed it,
* stable_node has been updated to be the new regular
* stable_node. A collapse of the chain is indistinguishable
* from the case there was no chain in the stable
* rbtree. Otherwise stable_node is the chain and
* stable_node_dup is the dup to replace.
*/
if (stable_node_dup == stable_node) {
VM_BUG_ON(is_stable_node_dup(stable_node_dup));
/* chain is missing so create it */
stable_node = alloc_stable_node_chain(stable_node_dup,
root);
if (!stable_node)
return NULL;
}
/*
* Add this stable_node dup that was
* migrated to the stable_node chain
* of the current nid for this page
* content.
*/
VM_BUG_ON(!is_stable_node_dup(stable_node_dup));
VM_BUG_ON(page_node->head != &migrate_nodes);
list_del(&page_node->list);
DO_NUMA(page_node->nid = nid);
stable_node_chain_add_dup(page_node, stable_node);
goto out;
}
/*
* stable_tree_insert - insert stable tree node pointing to new ksm page
* into the stable tree.
*
* This function returns the stable tree node just allocated on success,
* NULL otherwise.
*/
static struct ksm_stable_node *stable_tree_insert(struct page *kpage)
{
int nid;
unsigned long kpfn;
struct rb_root *root;
struct rb_node **new;
struct rb_node *parent;
struct ksm_stable_node *stable_node, *stable_node_dup, *stable_node_any;
bool need_chain = false;
kpfn = page_to_pfn(kpage);
nid = get_kpfn_nid(kpfn);
root = root_stable_tree + nid;
again:
parent = NULL;
new = &root->rb_node;
while (*new) {
struct page *tree_page;
int ret;
cond_resched();
stable_node = rb_entry(*new, struct ksm_stable_node, node);
stable_node_any = NULL;
tree_page = chain(&stable_node_dup, stable_node, root);
if (!stable_node_dup) {
/*
* Either all stable_node dups were full in
* this stable_node chain, or this chain was
* empty and should be rb_erased.
*/
stable_node_any = stable_node_dup_any(stable_node,
root);
if (!stable_node_any) {
/* rb_erase just run */
goto again;
}
/*
* Take any of the stable_node dups page of
* this stable_node chain to let the tree walk
* continue. All KSM pages belonging to the
* stable_node dups in a stable_node chain
* have the same content and they're
* write protected at all times. Any will work
* fine to continue the walk.
*/
tree_page = get_ksm_page(stable_node_any,
GET_KSM_PAGE_NOLOCK);
}
VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
if (!tree_page) {
/*
* If we walked over a stale stable_node,
* get_ksm_page() will call rb_erase() and it
* may rebalance the tree from under us. So
* restart the search from scratch. Returning
* NULL would be safe too, but we'd generate
* false negative insertions just because some
* stable_node was stale.
*/
goto again;
}
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 {
need_chain = true;
break;
}
}
stable_node_dup = alloc_stable_node();
if (!stable_node_dup)
return NULL;
INIT_HLIST_HEAD(&stable_node_dup->hlist);
stable_node_dup->kpfn = kpfn;
set_page_stable_node(kpage, stable_node_dup);
stable_node_dup->rmap_hlist_len = 0;
DO_NUMA(stable_node_dup->nid = nid);
if (!need_chain) {
rb_link_node(&stable_node_dup->node, parent, new);
rb_insert_color(&stable_node_dup->node, root);
} else {
if (!is_stable_node_chain(stable_node)) {
struct ksm_stable_node *orig = stable_node;
/* chain is missing so create it */
stable_node = alloc_stable_node_chain(orig, root);
if (!stable_node) {
free_stable_node(stable_node_dup);
return NULL;
}
}
stable_node_chain_add_dup(stable_node_dup, stable_node);
}
return stable_node_dup;
}
/*
* 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 ksm_rmap_item *unstable_tree_search_insert(struct ksm_rmap_item *rmap_item,
struct page *page,
struct page **tree_pagep)
{
struct rb_node **new;
struct rb_root *root;
struct rb_node *parent = NULL;
int nid;
nid = get_kpfn_nid(page_to_pfn(page));
root = root_unstable_tree + nid;
new = &root->rb_node;
while (*new) {
struct ksm_rmap_item *tree_rmap_item;
struct page *tree_page;
int ret;
cond_resched();
tree_rmap_item = rb_entry(*new, struct ksm_rmap_item, node);
tree_page = get_mergeable_page(tree_rmap_item);
if (!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 if (!ksm_merge_across_nodes &&
page_to_nid(tree_page) != nid) {
/*
* If tree_page has been migrated to another NUMA node,
* it will be flushed out and put in the right unstable
* tree next time: only merge with it when across_nodes.
*/
put_page(tree_page);
return NULL;
} else {
*tree_pagep = tree_page;
return tree_rmap_item;
}
}
rmap_item->address |= UNSTABLE_FLAG;
rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
DO_NUMA(rmap_item->nid = nid);
rb_link_node(&rmap_item->node, parent, new);
rb_insert_color(&rmap_item->node, root);
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 ksm_rmap_item *rmap_item,
struct ksm_stable_node *stable_node,
bool max_page_sharing_bypass)
{
/*
* rmap won't find this mapping if we don't insert the
* rmap_item in the right stable_node
* duplicate. page_migration could break later if rmap breaks,
* so we can as well crash here. We really need to check for
* rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check
* for other negative values as an underflow if detected here
* for the first time (and not when decreasing rmap_hlist_len)
* would be sign of memory corruption in the stable_node.
*/
BUG_ON(stable_node->rmap_hlist_len < 0);
stable_node->rmap_hlist_len++;
if (!max_page_sharing_bypass)
/* possibly non fatal but unexpected overflow, only warn */
WARN_ON_ONCE(stable_node->rmap_hlist_len >
ksm_max_page_sharing);
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++;
rmap_item->mm->ksm_merging_pages++;
}
/*
* 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 ksm_rmap_item *rmap_item)
{
struct mm_struct *mm = rmap_item->mm;
struct ksm_rmap_item *tree_rmap_item;
struct page *tree_page = NULL;
struct ksm_stable_node *stable_node;
struct page *kpage;
unsigned int checksum;
int err;
bool max_page_sharing_bypass = false;
stable_node = page_stable_node(page);
if (stable_node) {
if (stable_node->head != &migrate_nodes &&
get_kpfn_nid(READ_ONCE(stable_node->kpfn)) !=
NUMA(stable_node->nid)) {
stable_node_dup_del(stable_node);
stable_node->head = &migrate_nodes;
list_add(&stable_node->list, stable_node->head);
}
if (stable_node->head != &migrate_nodes &&
rmap_item->head == stable_node)
return;
/*
* If it's a KSM fork, allow it to go over the sharing limit
* without warnings.
*/
if (!is_page_sharing_candidate(stable_node))
max_page_sharing_bypass = true;
}
/* We first start with searching the page inside the stable tree */
kpage = stable_tree_search(page);
if (kpage == page && rmap_item->head == stable_node) {
put_page(kpage);
return;
}
remove_rmap_item_from_tree(rmap_item);
if (kpage) {
if (PTR_ERR(kpage) == -EBUSY)
return;
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),
max_page_sharing_bypass);
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;
}
/*
* Same checksum as an empty page. We attempt to merge it with the
* appropriate zero page if the user enabled this via sysfs.
*/
if (ksm_use_zero_pages && (checksum == zero_checksum)) {
struct vm_area_struct *vma;
mmap_read_lock(mm);
vma = find_mergeable_vma(mm, rmap_item->address);
if (vma) {
err = try_to_merge_one_page(vma, page,
ZERO_PAGE(rmap_item->address));
trace_ksm_merge_one_page(
page_to_pfn(ZERO_PAGE(rmap_item->address)),
rmap_item, mm, err);
} else {
/*
* If the vma is out of date, we do not need to
* continue.
*/
err = 0;
}
mmap_read_unlock(mm);
/*
* In case of failure, the page was not really empty, so we
* need to continue. Otherwise we're done.
*/
if (!err)
return;
}
tree_rmap_item =
unstable_tree_search_insert(rmap_item, page, &tree_page);
if (tree_rmap_item) {
bool split;
kpage = try_to_merge_two_pages(rmap_item, page,
tree_rmap_item, tree_page);
/*
* If both pages we tried to merge belong to the same compound
* page, then we actually ended up increasing the reference
* count of the same compound page twice, and split_huge_page
* failed.
* Here we set a flag if that happened, and we use it later to
* try split_huge_page again. Since we call put_page right
* afterwards, the reference count will be correct and
* split_huge_page should succeed.
*/
split = PageTransCompound(page)
&& compound_head(page) == compound_head(tree_page);
put_page(tree_page);
if (kpage) {
/*
* The pages were successfully merged: insert new
* node in the stable tree and add both rmap_items.
*/
lock_page(kpage);
stable_node = stable_tree_insert(kpage);
if (stable_node) {
stable_tree_append(tree_rmap_item, stable_node,
false);
stable_tree_append(rmap_item, stable_node,
false);
}
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);
}
} else if (split) {
/*
* We are here if we tried to merge two pages and
* failed because they both belonged to the same
* compound page. We will split the page now, but no
* merging will take place.
* We do not want to add the cost of a full lock; if
* the page is locked, it is better to skip it and
* perhaps try again later.
*/
if (!trylock_page(page))
return;
split_huge_page(page);
unlock_page(page);
}
}
}
static struct ksm_rmap_item *get_next_rmap_item(struct ksm_mm_slot *mm_slot,
struct ksm_rmap_item **rmap_list,
unsigned long addr)
{
struct ksm_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->slot.mm;
rmap_item->mm->ksm_rmap_items++;
rmap_item->address = addr;
rmap_item->rmap_list = *rmap_list;
*rmap_list = rmap_item;
}
return rmap_item;
}
/*
* Calculate skip age for the ksm page age. The age determines how often
* de-duplicating has already been tried unsuccessfully. If the age is
* smaller, the scanning of this page is skipped for less scans.
*
* @age: rmap_item age of page
*/
static unsigned int skip_age(rmap_age_t age)
{
if (age <= 3)
return 1;
if (age <= 5)
return 2;
if (age <= 8)
return 4;
return 8;
}
/*
* Determines if a page should be skipped for the current scan.
*
* @page: page to check
* @rmap_item: associated rmap_item of page
*/
static bool should_skip_rmap_item(struct page *page,
struct ksm_rmap_item *rmap_item)
{
rmap_age_t age;
if (!ksm_smart_scan)
return false;
/*
* Never skip pages that are already KSM; pages cmp_and_merge_page()
* will essentially ignore them, but we still have to process them
* properly.
*/
if (PageKsm(page))
return false;
age = rmap_item->age;
if (age != U8_MAX)
rmap_item->age++;
/*
* Smaller ages are not skipped, they need to get a chance to go
* through the different phases of the KSM merging.
*/
if (age < 3)
return false;
/*
* Are we still allowed to skip? If not, then don't skip it
* and determine how much more often we are allowed to skip next.
*/
if (!rmap_item->remaining_skips) {
rmap_item->remaining_skips = skip_age(age);
return false;
}
/* Skip this page */
ksm_pages_skipped++;
rmap_item->remaining_skips--;
remove_rmap_item_from_tree(rmap_item);
return true;
}
static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
{
struct mm_struct *mm;
struct ksm_mm_slot *mm_slot;
struct mm_slot *slot;
struct vm_area_struct *vma;
struct ksm_rmap_item *rmap_item;
struct vma_iterator vmi;
int nid;
if (list_empty(&ksm_mm_head.slot.mm_node))
return NULL;
mm_slot = ksm_scan.mm_slot;
if (mm_slot == &ksm_mm_head) {
trace_ksm_start_scan(ksm_scan.seqnr, ksm_rmap_items);
/*
* A number of pages can hang around indefinitely in per-cpu
* LRU cache, 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();
/*
* Whereas stale stable_nodes on the stable_tree itself
* get pruned in the regular course of stable_tree_search(),
* those moved out to the migrate_nodes list can accumulate:
* so prune them once before each full scan.
*/
if (!ksm_merge_across_nodes) {
struct ksm_stable_node *stable_node, *next;
struct page *page;
list_for_each_entry_safe(stable_node, next,
&migrate_nodes, list) {
page = get_ksm_page(stable_node,
GET_KSM_PAGE_NOLOCK);
if (page)
put_page(page);
cond_resched();
}
}
for (nid = 0; nid < ksm_nr_node_ids; nid++)
root_unstable_tree[nid] = RB_ROOT;
spin_lock(&ksm_mmlist_lock);
slot = list_entry(mm_slot->slot.mm_node.next,
struct mm_slot, mm_node);
mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
ksm_scan.mm_slot = mm_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 (mm_slot == &ksm_mm_head)
return NULL;
next_mm:
ksm_scan.address = 0;
ksm_scan.rmap_list = &mm_slot->rmap_list;
}
slot = &mm_slot->slot;
mm = slot->mm;
vma_iter_init(&vmi, mm, ksm_scan.address);
mmap_read_lock(mm);
if (ksm_test_exit(mm))
goto no_vmas;
for_each_vma(vmi, vma) {
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 (is_zone_device_page(*page))
goto next_page;
if (PageAnon(*page)) {
flush_anon_page(vma, *page, ksm_scan.address);
flush_dcache_page(*page);
rmap_item = get_next_rmap_item(mm_slot,
ksm_scan.rmap_list, ksm_scan.address);
if (rmap_item) {
ksm_scan.rmap_list =
&rmap_item->rmap_list;
if (should_skip_rmap_item(*page, rmap_item))
goto next_page;
ksm_scan.address += PAGE_SIZE;
} else
put_page(*page);
mmap_read_unlock(mm);
return rmap_item;
}
next_page:
put_page(*page);
ksm_scan.address += PAGE_SIZE;
cond_resched();
}
}
if (ksm_test_exit(mm)) {
no_vmas:
ksm_scan.address = 0;
ksm_scan.rmap_list = &mm_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(ksm_scan.rmap_list);
spin_lock(&ksm_mmlist_lock);
slot = list_entry(mm_slot->slot.mm_node.next,
struct mm_slot, mm_node);
ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
if (ksm_scan.address == 0) {
/*
* We've completed a full scan of all vmas, holding mmap_lock
* 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_lock then protects against race with MADV_MERGEABLE).
*/
hash_del(&mm_slot->slot.hash);
list_del(&mm_slot->slot.mm_node);
spin_unlock(&ksm_mmlist_lock);
mm_slot_free(mm_slot_cache, mm_slot);
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
mmap_read_unlock(mm);
mmdrop(mm);
} else {
mmap_read_unlock(mm);
/*
* mmap_read_unlock(mm) first because after
* spin_unlock(&ksm_mmlist_lock) run, the "mm" may
* already have been freed under us by __ksm_exit()
* because the "mm_slot" is still hashed and
* ksm_scan.mm_slot doesn't point to it anymore.
*/
spin_unlock(&ksm_mmlist_lock);
}
/* Repeat until we've completed scanning the whole list */
mm_slot = ksm_scan.mm_slot;
if (mm_slot != &ksm_mm_head)
goto next_mm;
trace_ksm_stop_scan(ksm_scan.seqnr, ksm_rmap_items);
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 ksm_rmap_item *rmap_item;
struct page *page;
unsigned int npages = scan_npages;
while (npages-- && likely(!freezing(current))) {
cond_resched();
rmap_item = scan_get_next_rmap_item(&page);
if (!rmap_item)
return;
cmp_and_merge_page(page, rmap_item);
put_page(page);
}
ksm_pages_scanned += scan_npages - npages;
}
static int ksmd_should_run(void)
{
return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.slot.mm_node);
}
static int ksm_scan_thread(void *nothing)
{
unsigned int sleep_ms;
set_freezable();
set_user_nice(current, 5);
while (!kthread_should_stop()) {
mutex_lock(&ksm_thread_mutex);
wait_while_offlining();
if (ksmd_should_run())
ksm_do_scan(ksm_thread_pages_to_scan);
mutex_unlock(&ksm_thread_mutex);
try_to_freeze();
if (ksmd_should_run()) {
sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs);
wait_event_interruptible_timeout(ksm_iter_wait,
sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs),
msecs_to_jiffies(sleep_ms));
} else {
wait_event_freezable(ksm_thread_wait,
ksmd_should_run() || kthread_should_stop());
}
}
return 0;
}
static void __ksm_add_vma(struct vm_area_struct *vma)
{
unsigned long vm_flags = vma->vm_flags;
if (vm_flags & VM_MERGEABLE)
return;
if (vma_ksm_compatible(vma))
vm_flags_set(vma, VM_MERGEABLE);
}
static int __ksm_del_vma(struct vm_area_struct *vma)
{
int err;
if (!(vma->vm_flags & VM_MERGEABLE))
return 0;
if (vma->anon_vma) {
err = unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end, true);
if (err)
return err;
}
vm_flags_clear(vma, VM_MERGEABLE);
return 0;
}
/**
* ksm_add_vma - Mark vma as mergeable if compatible
*
* @vma: Pointer to vma
*/
void ksm_add_vma(struct vm_area_struct *vma)
{
struct mm_struct *mm = vma->vm_mm;
if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
__ksm_add_vma(vma);
}
static void ksm_add_vmas(struct mm_struct *mm)
{
struct vm_area_struct *vma;
VMA_ITERATOR(vmi, mm, 0);
for_each_vma(vmi, vma)
__ksm_add_vma(vma);
}
static int ksm_del_vmas(struct mm_struct *mm)
{
struct vm_area_struct *vma;
int err;
VMA_ITERATOR(vmi, mm, 0);
for_each_vma(vmi, vma) {
err = __ksm_del_vma(vma);
if (err)
return err;
}
return 0;
}
/**
* ksm_enable_merge_any - Add mm to mm ksm list and enable merging on all
* compatible VMA's
*
* @mm: Pointer to mm
*
* Returns 0 on success, otherwise error code
*/
int ksm_enable_merge_any(struct mm_struct *mm)
{
int err;
if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
return 0;
if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
err = __ksm_enter(mm);
if (err)
return err;
}
set_bit(MMF_VM_MERGE_ANY, &mm->flags);
ksm_add_vmas(mm);
return 0;
}
/**
* ksm_disable_merge_any - Disable merging on all compatible VMA's of the mm,
* previously enabled via ksm_enable_merge_any().
*
* Disabling merging implies unmerging any merged pages, like setting
* MADV_UNMERGEABLE would. If unmerging fails, the whole operation fails and
* merging on all compatible VMA's remains enabled.
*
* @mm: Pointer to mm
*
* Returns 0 on success, otherwise error code
*/
int ksm_disable_merge_any(struct mm_struct *mm)
{
int err;
if (!test_bit(MMF_VM_MERGE_ANY, &mm->flags))
return 0;
err = ksm_del_vmas(mm);
if (err) {
ksm_add_vmas(mm);
return err;
}
clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
return 0;
}
int ksm_disable(struct mm_struct *mm)
{
mmap_assert_write_locked(mm);
if (!test_bit(MMF_VM_MERGEABLE, &mm->flags))
return 0;
if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
return ksm_disable_merge_any(mm);
return ksm_del_vmas(mm);
}
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:
if (vma->vm_flags & VM_MERGEABLE)
return 0;
if (!vma_ksm_compatible(vma))
return 0;
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, true);
if (err)
return err;
}
*vm_flags &= ~VM_MERGEABLE;
break;
}
return 0;
}
EXPORT_SYMBOL_GPL(ksm_madvise);
int __ksm_enter(struct mm_struct *mm)
{
struct ksm_mm_slot *mm_slot;
struct mm_slot *slot;
int needs_wakeup;
mm_slot = mm_slot_alloc(mm_slot_cache);
if (!mm_slot)
return -ENOMEM;
slot = &mm_slot->slot;
/* Check ksm_run too? Would need tighter locking */
needs_wakeup = list_empty(&ksm_mm_head.slot.mm_node);
spin_lock(&ksm_mmlist_lock);
mm_slot_insert(mm_slots_hash, mm, slot);
/*
* When KSM_RUN_MERGE (or KSM_RUN_STOP),
* 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.
*
* But when KSM_RUN_UNMERGE, it's important to insert ahead of its
* scanning cursor, otherwise KSM pages in newly forked mms will be
* missed: then we might as well insert at the end of the list.
*/
if (ksm_run & KSM_RUN_UNMERGE)
list_add_tail(&slot->mm_node, &ksm_mm_head.slot.mm_node);
else
list_add_tail(&slot->mm_node, &ksm_scan.mm_slot->slot.mm_node);
spin_unlock(&ksm_mmlist_lock);
set_bit(MMF_VM_MERGEABLE, &mm->flags);
mmgrab(mm);
if (needs_wakeup)
wake_up_interruptible(&ksm_thread_wait);
trace_ksm_enter(mm);
return 0;
}
void __ksm_exit(struct mm_struct *mm)
{
struct ksm_mm_slot *mm_slot;
struct mm_slot *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_lock 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);
slot = mm_slot_lookup(mm_slots_hash, mm);
mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
if (mm_slot && ksm_scan.mm_slot != mm_slot) {
if (!mm_slot->rmap_list) {
hash_del(&slot->hash);
list_del(&slot->mm_node);
easy_to_free = 1;
} else {
list_move(&slot->mm_node,
&ksm_scan.mm_slot->slot.mm_node);
}
}
spin_unlock(&ksm_mmlist_lock);
if (easy_to_free) {
mm_slot_free(mm_slot_cache, mm_slot);
clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
mmdrop(mm);
} else if (mm_slot) {
mmap_write_lock(mm);
mmap_write_unlock(mm);
}
trace_ksm_exit(mm);
}
struct page *ksm_might_need_to_copy(struct page *page,
struct vm_area_struct *vma, unsigned long address)
{
struct folio *folio = page_folio(page);
struct anon_vma *anon_vma = folio_anon_vma(folio);
struct page *new_page;
if (PageKsm(page)) {
if (page_stable_node(page) &&
!(ksm_run & KSM_RUN_UNMERGE))
return page; /* no need to copy it */
} else if (!anon_vma) {
return page; /* no need to copy it */
} else if (page->index == linear_page_index(vma, address) &&
anon_vma->root == vma->anon_vma->root) {
return page; /* still no need to copy it */
}
if (PageHWPoison(page))
return ERR_PTR(-EHWPOISON);
if (!PageUptodate(page))
return page; /* let do_swap_page report the error */
new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
if (new_page &&
mem_cgroup_charge(page_folio(new_page), vma->vm_mm, GFP_KERNEL)) {
put_page(new_page);
new_page = NULL;
}
if (new_page) {
if (copy_mc_user_highpage(new_page, page, address, vma)) {
put_page(new_page);
memory_failure_queue(page_to_pfn(page), 0);
return ERR_PTR(-EHWPOISON);
}
SetPageDirty(new_page);
__SetPageUptodate(new_page);
__SetPageLocked(new_page);
#ifdef CONFIG_SWAP
count_vm_event(KSM_SWPIN_COPY);
#endif
}
return new_page;
}
void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc)
{
struct ksm_stable_node *stable_node;
struct ksm_rmap_item *rmap_item;
int search_new_forks = 0;
VM_BUG_ON_FOLIO(!folio_test_ksm(folio), folio);
/*
* Rely on the page lock to protect against concurrent modifications
* to that page's node of the stable tree.
*/
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
stable_node = folio_stable_node(folio);
if (!stable_node)
return;
again:
hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
struct anon_vma *anon_vma = rmap_item->anon_vma;
struct anon_vma_chain *vmac;
struct vm_area_struct *vma;
cond_resched();
if (!anon_vma_trylock_read(anon_vma)) {
if (rwc->try_lock) {
rwc->contended = true;
return;
}
anon_vma_lock_read(anon_vma);
}
anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
0, ULONG_MAX) {
unsigned long addr;
cond_resched();
vma = vmac->vma;
/* Ignore the stable/unstable/sqnr flags */
addr = rmap_item->address & PAGE_MASK;
if (addr < vma->vm_start || addr >= 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 (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
continue;
if (!rwc->rmap_one(folio, vma, addr, rwc->arg)) {
anon_vma_unlock_read(anon_vma);
return;
}
if (rwc->done && rwc->done(folio)) {
anon_vma_unlock_read(anon_vma);
return;
}
}
anon_vma_unlock_read(anon_vma);
}
if (!search_new_forks++)
goto again;
}
#ifdef CONFIG_MEMORY_FAILURE
/*
* Collect processes when the error hit an ksm page.
*/
void collect_procs_ksm(struct page *page, struct list_head *to_kill,
int force_early)
{
struct ksm_stable_node *stable_node;
struct ksm_rmap_item *rmap_item;
struct folio *folio = page_folio(page);
struct vm_area_struct *vma;
struct task_struct *tsk;
stable_node = folio_stable_node(folio);
if (!stable_node)
return;
hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
struct anon_vma *av = rmap_item->anon_vma;
anon_vma_lock_read(av);
rcu_read_lock();
for_each_process(tsk) {
struct anon_vma_chain *vmac;
unsigned long addr;
struct task_struct *t =
task_early_kill(tsk, force_early);
if (!t)
continue;
anon_vma_interval_tree_foreach(vmac, &av->rb_root, 0,
ULONG_MAX)
{
vma = vmac->vma;
if (vma->vm_mm == t->mm) {
addr = rmap_item->address & PAGE_MASK;
add_to_kill_ksm(t, page, vma, to_kill,
addr);
}
}
}
rcu_read_unlock();
anon_vma_unlock_read(av);
}
}
#endif
#ifdef CONFIG_MIGRATION
void folio_migrate_ksm(struct folio *newfolio, struct folio *folio)
{
struct ksm_stable_node *stable_node;
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
VM_BUG_ON_FOLIO(!folio_test_locked(newfolio), newfolio);
VM_BUG_ON_FOLIO(newfolio->mapping != folio->mapping, newfolio);
stable_node = folio_stable_node(folio);
if (stable_node) {
VM_BUG_ON_FOLIO(stable_node->kpfn != folio_pfn(folio), folio);
stable_node->kpfn = folio_pfn(newfolio);
/*
* newfolio->mapping was set in advance; now we need smp_wmb()
* to make sure that the new stable_node->kpfn is visible
* to get_ksm_page() before it can see that folio->mapping
* has gone stale (or that folio_test_swapcache has been cleared).
*/
smp_wmb();
set_page_stable_node(&folio->page, NULL);
}
}
#endif /* CONFIG_MIGRATION */
#ifdef CONFIG_MEMORY_HOTREMOVE
static void wait_while_offlining(void)
{
while (ksm_run & KSM_RUN_OFFLINE) {
mutex_unlock(&ksm_thread_mutex);
wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
TASK_UNINTERRUPTIBLE);
mutex_lock(&ksm_thread_mutex);
}
}
static bool stable_node_dup_remove_range(struct ksm_stable_node *stable_node,
unsigned long start_pfn,
unsigned long end_pfn)
{
if (stable_node->kpfn >= start_pfn &&
stable_node->kpfn < end_pfn) {
/*
* Don't get_ksm_page, page has already gone:
* which is why we keep kpfn instead of page*
*/
remove_node_from_stable_tree(stable_node);
return true;
}
return false;
}
static bool stable_node_chain_remove_range(struct ksm_stable_node *stable_node,
unsigned long start_pfn,
unsigned long end_pfn,
struct rb_root *root)
{
struct ksm_stable_node *dup;
struct hlist_node *hlist_safe;
if (!is_stable_node_chain(stable_node)) {
VM_BUG_ON(is_stable_node_dup(stable_node));
return stable_node_dup_remove_range(stable_node, start_pfn,
end_pfn);
}
hlist_for_each_entry_safe(dup, hlist_safe,
&stable_node->hlist, hlist_dup) {
VM_BUG_ON(!is_stable_node_dup(dup));
stable_node_dup_remove_range(dup, start_pfn, end_pfn);
}
if (hlist_empty(&stable_node->hlist)) {
free_stable_node_chain(stable_node, root);
return true; /* notify caller that tree was rebalanced */
} else
return false;
}
static void ksm_check_stable_tree(unsigned long start_pfn,
unsigned long end_pfn)
{
struct ksm_stable_node *stable_node, *next;
struct rb_node *node;
int nid;
for (nid = 0; nid < ksm_nr_node_ids; nid++) {
node = rb_first(root_stable_tree + nid);
while (node) {
stable_node = rb_entry(node, struct ksm_stable_node, node);
if (stable_node_chain_remove_range(stable_node,
start_pfn, end_pfn,
root_stable_tree +
nid))
node = rb_first(root_stable_tree + nid);
else
node = rb_next(node);
cond_resched();
}
}
list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
if (stable_node->kpfn >= start_pfn &&
stable_node->kpfn < end_pfn)
remove_node_from_stable_tree(stable_node);
cond_resched();
}
}
static int ksm_memory_callback(struct notifier_block *self,
unsigned long action, void *arg)
{
struct memory_notify *mn = arg;
switch (action) {
case MEM_GOING_OFFLINE:
/*
* Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
* and remove_all_stable_nodes() while memory is going offline:
* it is unsafe for them to touch the stable tree at this time.
* But unmerge_ksm_pages(), rmap lookups and other entry points
* which do not need the ksm_thread_mutex are all safe.
*/
mutex_lock(&ksm_thread_mutex);
ksm_run |= KSM_RUN_OFFLINE;
mutex_unlock(&ksm_thread_mutex);
break;
case MEM_OFFLINE:
/*
* Most of the work is done by page migration; but there might
* be a few stable_nodes left over, still pointing to struct
* pages which have been offlined: prune those from the tree,
* otherwise get_ksm_page() might later try to access a
* non-existent struct page.
*/
ksm_check_stable_tree(mn->start_pfn,
mn->start_pfn + mn->nr_pages);
fallthrough;
case MEM_CANCEL_OFFLINE:
mutex_lock(&ksm_thread_mutex);
ksm_run &= ~KSM_RUN_OFFLINE;
mutex_unlock(&ksm_thread_mutex);
smp_mb(); /* wake_up_bit advises this */
wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
break;
}
return NOTIFY_OK;
}
#else
static void wait_while_offlining(void)
{
}
#endif /* CONFIG_MEMORY_HOTREMOVE */
#ifdef CONFIG_PROC_FS
long ksm_process_profit(struct mm_struct *mm)
{
return (long)(mm->ksm_merging_pages + mm->ksm_zero_pages) * PAGE_SIZE -
mm->ksm_rmap_items * sizeof(struct ksm_rmap_item);
}
#endif /* CONFIG_PROC_FS */
#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_RW(_name)
static ssize_t sleep_millisecs_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(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 int msecs;
int err;
err = kstrtouint(buf, 10, &msecs);
if (err)
return -EINVAL;
ksm_thread_sleep_millisecs = msecs;
wake_up_interruptible(&ksm_iter_wait);
return count;
}
KSM_ATTR(sleep_millisecs);
static ssize_t pages_to_scan_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(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)
{
unsigned int nr_pages;
int err;
err = kstrtouint(buf, 10, &nr_pages);
if (err)
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 sysfs_emit(buf, "%lu\n", ksm_run);
}
static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
const char *buf, size_t count)
{
unsigned int flags;
int err;
err = kstrtouint(buf, 10, &flags);
if (err)
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);
wait_while_offlining();
if (ksm_run != flags) {
ksm_run = flags;
if (flags & KSM_RUN_UNMERGE) {
set_current_oom_origin();
err = unmerge_and_remove_all_rmap_items();
clear_current_oom_origin();
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);
#ifdef CONFIG_NUMA
static ssize_t merge_across_nodes_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%u\n", ksm_merge_across_nodes);
}
static ssize_t merge_across_nodes_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
unsigned long knob;
err = kstrtoul(buf, 10, &knob);
if (err)
return err;
if (knob > 1)
return -EINVAL;
mutex_lock(&ksm_thread_mutex);
wait_while_offlining();
if (ksm_merge_across_nodes != knob) {
if (ksm_pages_shared || remove_all_stable_nodes())
err = -EBUSY;
else if (root_stable_tree == one_stable_tree) {
struct rb_root *buf;
/*
* This is the first time that we switch away from the
* default of merging across nodes: must now allocate
* a buffer to hold as many roots as may be needed.
* Allocate stable and unstable together:
* MAXSMP NODES_SHIFT 10 will use 16kB.
*/
buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
GFP_KERNEL);
/* Let us assume that RB_ROOT is NULL is zero */
if (!buf)
err = -ENOMEM;
else {
root_stable_tree = buf;
root_unstable_tree = buf + nr_node_ids;
/* Stable tree is empty but not the unstable */
root_unstable_tree[0] = one_unstable_tree[0];
}
}
if (!err) {
ksm_merge_across_nodes = knob;
ksm_nr_node_ids = knob ? 1 : nr_node_ids;
}
}
mutex_unlock(&ksm_thread_mutex);
return err ? err : count;
}
KSM_ATTR(merge_across_nodes);
#endif
static ssize_t use_zero_pages_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%u\n", ksm_use_zero_pages);
}
static ssize_t use_zero_pages_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
bool value;
err = kstrtobool(buf, &value);
if (err)
return -EINVAL;
ksm_use_zero_pages = value;
return count;
}
KSM_ATTR(use_zero_pages);
static ssize_t max_page_sharing_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%u\n", ksm_max_page_sharing);
}
static ssize_t max_page_sharing_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
int knob;
err = kstrtoint(buf, 10, &knob);
if (err)
return err;
/*
* When a KSM page is created it is shared by 2 mappings. This
* being a signed comparison, it implicitly verifies it's not
* negative.
*/
if (knob < 2)
return -EINVAL;
if (READ_ONCE(ksm_max_page_sharing) == knob)
return count;
mutex_lock(&ksm_thread_mutex);
wait_while_offlining();
if (ksm_max_page_sharing != knob) {
if (ksm_pages_shared || remove_all_stable_nodes())
err = -EBUSY;
else
ksm_max_page_sharing = knob;
}
mutex_unlock(&ksm_thread_mutex);
return err ? err : count;
}
KSM_ATTR(max_page_sharing);
static ssize_t pages_scanned_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%lu\n", ksm_pages_scanned);
}
KSM_ATTR_RO(pages_scanned);
static ssize_t pages_shared_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(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 sysfs_emit(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 sysfs_emit(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 sysfs_emit(buf, "%ld\n", ksm_pages_volatile);
}
KSM_ATTR_RO(pages_volatile);
static ssize_t pages_skipped_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%lu\n", ksm_pages_skipped);
}
KSM_ATTR_RO(pages_skipped);
static ssize_t ksm_zero_pages_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%ld\n", ksm_zero_pages);
}
KSM_ATTR_RO(ksm_zero_pages);
static ssize_t general_profit_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
long general_profit;
general_profit = (ksm_pages_sharing + ksm_zero_pages) * PAGE_SIZE -
ksm_rmap_items * sizeof(struct ksm_rmap_item);
return sysfs_emit(buf, "%ld\n", general_profit);
}
KSM_ATTR_RO(general_profit);
static ssize_t stable_node_dups_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%lu\n", ksm_stable_node_dups);
}
KSM_ATTR_RO(stable_node_dups);
static ssize_t stable_node_chains_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%lu\n", ksm_stable_node_chains);
}
KSM_ATTR_RO(stable_node_chains);
static ssize_t
stable_node_chains_prune_millisecs_show(struct kobject *kobj,
struct kobj_attribute *attr,
char *buf)
{
return sysfs_emit(buf, "%u\n", ksm_stable_node_chains_prune_millisecs);
}
static ssize_t
stable_node_chains_prune_millisecs_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
unsigned int msecs;
int err;
err = kstrtouint(buf, 10, &msecs);
if (err)
return -EINVAL;
ksm_stable_node_chains_prune_millisecs = msecs;
return count;
}
KSM_ATTR(stable_node_chains_prune_millisecs);
static ssize_t full_scans_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%lu\n", ksm_scan.seqnr);
}
KSM_ATTR_RO(full_scans);
static ssize_t smart_scan_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%u\n", ksm_smart_scan);
}
static ssize_t smart_scan_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
bool value;
err = kstrtobool(buf, &value);
if (err)
return -EINVAL;
ksm_smart_scan = value;
return count;
}
KSM_ATTR(smart_scan);
static struct attribute *ksm_attrs[] = {
&sleep_millisecs_attr.attr,
&pages_to_scan_attr.attr,
&run_attr.attr,
&pages_scanned_attr.attr,
&pages_shared_attr.attr,
&pages_sharing_attr.attr,
&pages_unshared_attr.attr,
&pages_volatile_attr.attr,
&pages_skipped_attr.attr,
&ksm_zero_pages_attr.attr,
&full_scans_attr.attr,
#ifdef CONFIG_NUMA
&merge_across_nodes_attr.attr,
#endif
&max_page_sharing_attr.attr,
&stable_node_chains_attr.attr,
&stable_node_dups_attr.attr,
&stable_node_chains_prune_millisecs_attr.attr,
&use_zero_pages_attr.attr,
&general_profit_attr.attr,
&smart_scan_attr.attr,
NULL,
};
static const 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;
/* The correct value depends on page size and endianness */
zero_checksum = calc_checksum(ZERO_PAGE(0));
/* Default to false for backwards compatibility */
ksm_use_zero_pages = false;
err = ksm_slab_init();
if (err)
goto out;
ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
if (IS_ERR(ksm_thread)) {
pr_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) {
pr_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
/* There is no significance to this priority 100 */
hotplug_memory_notifier(ksm_memory_callback, KSM_CALLBACK_PRI);
#endif
return 0;
out_free:
ksm_slab_free();
out:
return err;
}
subsys_initcall(ksm_init);