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kernel / pub / scm / linux / kernel / git / gregkh / tty / d21b26cad33250be758ea9d860ff9d5c3992c459 / . / mm / ksm.c
blob: 160787bb121cc0f718f871b40f53de38741aabc9 [file] [log] [blame]
// 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/cputime.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;
/* Default number of pages to scan per batch */
#define DEFAULT_PAGES_TO_SCAN 100
/* 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 = DEFAULT_PAGES_TO_SCAN;
/* 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 */
atomic_long_t ksm_zero_pages = ATOMIC_LONG_INIT(0);
/* The number of pages that have been skipped due to "smart scanning" */
static unsigned long ksm_pages_skipped;
/* Don't scan more than max pages per batch. */
static unsigned long ksm_advisor_max_pages_to_scan = 30000;
/* Min CPU for scanning pages per scan */
#define KSM_ADVISOR_MIN_CPU 10
/* Max CPU for scanning pages per scan */
static unsigned int ksm_advisor_max_cpu = 70;
/* Target scan time in seconds to analyze all KSM candidate pages. */
static unsigned long ksm_advisor_target_scan_time = 200;
/* Exponentially weighted moving average. */
#define EWMA_WEIGHT 30
/**
* struct advisor_ctx - metadata for KSM advisor
* @start_scan: start time of the current scan
* @scan_time: scan time of previous scan
* @change: change in percent to pages_to_scan parameter
* @cpu_time: cpu time consumed by the ksmd thread in the previous scan
*/
struct advisor_ctx {
ktime_t start_scan;
unsigned long scan_time;
unsigned long change;
unsigned long long cpu_time;
};
static struct advisor_ctx advisor_ctx;
/* Define different advisor's */
enum ksm_advisor_type {
KSM_ADVISOR_NONE,
KSM_ADVISOR_SCAN_TIME,
};
static enum ksm_advisor_type ksm_advisor;
#ifdef CONFIG_SYSFS
/*
* Only called through the sysfs control interface:
*/
/* At least scan this many pages per batch. */
static unsigned long ksm_advisor_min_pages_to_scan = 500;
static void set_advisor_defaults(void)
{
if (ksm_advisor == KSM_ADVISOR_NONE) {
ksm_thread_pages_to_scan = DEFAULT_PAGES_TO_SCAN;
} else if (ksm_advisor == KSM_ADVISOR_SCAN_TIME) {
advisor_ctx = (const struct advisor_ctx){ 0 };
ksm_thread_pages_to_scan = ksm_advisor_min_pages_to_scan;
}
}
#endif /* CONFIG_SYSFS */
static inline void advisor_start_scan(void)
{
if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
advisor_ctx.start_scan = ktime_get();
}
/*
* Use previous scan time if available, otherwise use current scan time as an
* approximation for the previous scan time.
*/
static inline unsigned long prev_scan_time(struct advisor_ctx *ctx,
unsigned long scan_time)
{
return ctx->scan_time ? ctx->scan_time : scan_time;
}
/* Calculate exponential weighted moving average */
static unsigned long ewma(unsigned long prev, unsigned long curr)
{
return ((100 - EWMA_WEIGHT) * prev + EWMA_WEIGHT * curr) / 100;
}
/*
* The scan time advisor is based on the current scan rate and the target
* scan rate.
*
* new_pages_to_scan = pages_to_scan * (scan_time / target_scan_time)
*
* To avoid perturbations it calculates a change factor of previous changes.
* A new change factor is calculated for each iteration and it uses an
* exponentially weighted moving average. The new pages_to_scan value is
* multiplied with that change factor:
*
* new_pages_to_scan *= change facor
*
* The new_pages_to_scan value is limited by the cpu min and max values. It
* calculates the cpu percent for the last scan and calculates the new
* estimated cpu percent cost for the next scan. That value is capped by the
* cpu min and max setting.
*
* In addition the new pages_to_scan value is capped by the max and min
* limits.
*/
static void scan_time_advisor(void)
{
unsigned int cpu_percent;
unsigned long cpu_time;
unsigned long cpu_time_diff;
unsigned long cpu_time_diff_ms;
unsigned long pages;
unsigned long per_page_cost;
unsigned long factor;
unsigned long change;
unsigned long last_scan_time;
unsigned long scan_time;
/* Convert scan time to seconds */
scan_time = div_s64(ktime_ms_delta(ktime_get(), advisor_ctx.start_scan),
MSEC_PER_SEC);
scan_time = scan_time ? scan_time : 1;
/* Calculate CPU consumption of ksmd background thread */
cpu_time = task_sched_runtime(current);
cpu_time_diff = cpu_time - advisor_ctx.cpu_time;
cpu_time_diff_ms = cpu_time_diff / 1000 / 1000;
cpu_percent = (cpu_time_diff_ms * 100) / (scan_time * 1000);
cpu_percent = cpu_percent ? cpu_percent : 1;
last_scan_time = prev_scan_time(&advisor_ctx, scan_time);
/* Calculate scan time as percentage of target scan time */
factor = ksm_advisor_target_scan_time * 100 / scan_time;
factor = factor ? factor : 1;
/*
* Calculate scan time as percentage of last scan time and use
* exponentially weighted average to smooth it
*/
change = scan_time * 100 / last_scan_time;
change = change ? change : 1;
change = ewma(advisor_ctx.change, change);
/* Calculate new scan rate based on target scan rate. */
pages = ksm_thread_pages_to_scan * 100 / factor;
/* Update pages_to_scan by weighted change percentage. */
pages = pages * change / 100;
/* Cap new pages_to_scan value */
per_page_cost = ksm_thread_pages_to_scan / cpu_percent;
per_page_cost = per_page_cost ? per_page_cost : 1;
pages = min(pages, per_page_cost * ksm_advisor_max_cpu);
pages = max(pages, per_page_cost * KSM_ADVISOR_MIN_CPU);
pages = min(pages, ksm_advisor_max_pages_to_scan);
/* Update advisor context */
advisor_ctx.change = change;
advisor_ctx.scan_time = scan_time;
advisor_ctx.cpu_time = cpu_time;
ksm_thread_pages_to_scan = pages;
trace_ksm_advisor(scan_time, pages, cpu_percent);
}
static void advisor_stop_scan(void)
{
if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
scan_time_advisor();
}
#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);
static int __init ksm_slab_init(void)
{
rmap_item_cache = KMEM_CACHE(ksm_rmap_item, 0);
if (!rmap_item_cache)
goto out;
stable_node_cache = KMEM_CACHE(ksm_stable_node, 0);
if (!stable_node_cache)
goto out_free1;
mm_slot_cache = 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;
}
/*
* 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;
if (lock_vma)
vma_start_write(vma);
do {
bool ksm_page = false;
struct folio_walk fw;
struct folio *folio;
cond_resched();
folio = folio_walk_start(&fw, vma, addr,
FW_MIGRATION | FW_ZEROPAGE);
if (folio) {
/* Small folio implies FW_LEVEL_PTE. */
if (!folio_test_large(folio) &&
(folio_test_ksm(folio) || is_ksm_zero_pte(fw.pte)))
ksm_page = true;
folio_walk_end(&fw, vma);
}
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 KSM page 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 ksm_compatible(const struct file *file, vm_flags_t vm_flags)
{
if (vm_flags & (VM_SHARED | VM_MAYSHARE | VM_SPECIAL |
VM_HUGETLB | VM_DROPPABLE))
return false; /* just ignore the advice */
if (file_is_dax(file))
return false;
#ifdef VM_SAO
if (vm_flags & VM_SAO)
return false;
#endif
#ifdef VM_SPARC_ADI
if (vm_flags & VM_SPARC_ADI)
return false;
#endif
return true;
}
static bool vma_ksm_compatible(struct vm_area_struct *vma)
{
return ksm_compatible(vma->vm_file, vma->vm_flags);
}
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 = NULL;
struct folio_walk fw;
struct folio *folio;
mmap_read_lock(mm);
vma = find_mergeable_vma(mm, addr);
if (!vma)
goto out;
folio = folio_walk_start(&fw, vma, addr, 0);
if (folio) {
if (!folio_is_zone_device(folio) &&
folio_test_anon(folio)) {
folio_get(folio);
page = fw.page;
}
folio_walk_end(&fw, vma);
}
out:
if (page) {
flush_anon_page(vma, page, addr);
flush_dcache_page(page);
}
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 ksm_get_folio_flags {
KSM_GET_FOLIO_NOLOCK,
KSM_GET_FOLIO_LOCK,
KSM_GET_FOLIO_TRYLOCK
};
/*
* ksm_get_folio: 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 folio *ksm_get_folio(struct ksm_stable_node *stable_node,
enum ksm_get_folio_flags flags)
{
struct folio *folio;
void *expected_mapping;
unsigned long kpfn;
expected_mapping = (void *)((unsigned long)stable_node |
FOLIO_MAPPING_KSM);
again:
kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */
folio = pfn_folio(kpfn);
if (READ_ONCE(folio->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 (!folio_try_get(folio)) {
/*
* Another check for folio->mapping != expected_mapping
* would work here too. We have chosen to test the
* swapcache flag to optimize the common case, when the
* folio is or is about to be freed: the swapcache flag
* is cleared (under spin_lock_irq) in the ref_freeze
* section of __remove_mapping(); but anon folio->mapping
* is reset to NULL later, in free_pages_prepare().
*/
if (!folio_test_swapcache(folio))
goto stale;
cpu_relax();
}
if (READ_ONCE(folio->mapping) != expected_mapping) {
folio_put(folio);
goto stale;
}
if (flags == KSM_GET_FOLIO_TRYLOCK) {
if (!folio_trylock(folio)) {
folio_put(folio);
return ERR_PTR(-EBUSY);
}
} else if (flags == KSM_GET_FOLIO_LOCK)
folio_lock(folio);
if (flags != KSM_GET_FOLIO_NOLOCK) {
if (READ_ONCE(folio->mapping) != expected_mapping) {
folio_unlock(folio);
folio_put(folio);
goto stale;
}
}
return folio;
stale:
/*
* We come here from above when folio->mapping or the swapcache flag
* 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 folio *folio;
stable_node = rmap_item->head;
folio = ksm_get_folio(stable_node, KSM_GET_FOLIO_LOCK);
if (!folio)
goto out;
hlist_del(&rmap_item->hlist);
folio_unlock(folio);
folio_put(folio);
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(const 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 folio_set_stable_node(struct folio *folio,
struct ksm_stable_node *stable_node)
{
VM_WARN_ON_FOLIO(folio_test_anon(folio) && PageAnonExclusive(&folio->page), folio);
folio->mapping = (void *)((unsigned long)stable_node | FOLIO_MAPPING_KSM);
}
#ifdef CONFIG_SYSFS
/*
* Only called through the sysfs control interface:
*/
static int remove_stable_node(struct ksm_stable_node *stable_node)
{
struct folio *folio;
int err;
folio = ksm_get_folio(stable_node, KSM_GET_FOLIO_LOCK);
if (!folio) {
/*
* ksm_get_folio 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 (!folio_mapped(folio)) {
/*
* The stable node did not yet appear stale to ksm_get_folio(),
* since that allows for an unmapped ksm folio to be recognized
* right up until it is freed; but the node is safe to remove.
* This folio might be in an LRU cache waiting to be freed,
* or it might be in the swapcache (perhaps under writeback),
* or it might have been removed from swapcache a moment ago.
*/
folio_set_stable_node(folio, NULL);
remove_node_from_stable_tree(stable_node);
err = 0;
}
folio_unlock(folio);
folio_put(folio);
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_local_page(page);
checksum = xxhash(addr, PAGE_SIZE, 0);
kunmap_local(addr);
return checksum;
}
static int write_protect_page(struct vm_area_struct *vma, struct folio *folio,
pte_t *orig_pte)
{
struct mm_struct *mm = vma->vm_mm;
DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, 0, 0);
int swapped;
int err = -EFAULT;
struct mmu_notifier_range range;
bool anon_exclusive;
pte_t entry;
if (WARN_ON_ONCE(folio_test_large(folio)))
return err;
pvmw.address = page_address_in_vma(folio, folio_page(folio, 0), vma);
if (pvmw.address == -EFAULT)
goto out;
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;
entry = ptep_get(pvmw.pte);
/*
* Handle PFN swap PTEs, such as device-exclusive ones, that actually
* map pages: give up just like the next folio_walk would.
*/
if (unlikely(!pte_present(entry)))
goto out_unlock;
anon_exclusive = PageAnonExclusive(&folio->page);
if (pte_write(entry) || pte_dirty(entry) ||
anon_exclusive || mm_tlb_flush_pending(mm)) {
swapped = folio_test_swapcache(folio);
flush_cache_page(vma, pvmw.address, folio_pfn(folio));
/*
* 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 (folio_mapcount(folio) + 1 + swapped != folio_ref_count(folio)) {
set_pte_at(mm, pvmw.address, pvmw.pte, entry);
goto out_unlock;
}
/* See folio_try_share_anon_rmap_pte(): clear PTE first. */
if (anon_exclusive &&
folio_try_share_anon_rmap_pte(folio, &folio->page)) {
set_pte_at(mm, pvmw.address, pvmw.pte, entry);
goto out_unlock;
}
if (pte_dirty(entry))
folio_mark_dirty(folio);
entry = pte_mkclean(entry);
if (pte_write(entry))
entry = pte_wrprotect(entry);
set_pte_at(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 folio *kfolio = page_folio(kpage);
struct mm_struct *mm = vma->vm_mm;
struct folio *folio = page_folio(page);
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(folio, 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_FOLIO(folio_test_anon(kfolio) && PageAnonExclusive(kpage),
kfolio);
/*
* 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))) {
folio_get(kfolio);
folio_add_anon_rmap_pte(kfolio, 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_map_zero_page(mm);
/*
* 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(mm, addr, ptep, newpte);
folio_remove_rmap_pte(folio, page, vma);
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 KSM 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)
{
struct folio *folio = page_folio(page);
pte_t orig_pte = __pte(0);
int err = -EFAULT;
if (page == kpage) /* ksm page forked */
return 0;
if (!folio_test_anon(folio))
goto out;
/*
* We need the folio lock to read a stable swapcache flag in
* write_protect_page(). We trylock 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 (!folio_trylock(folio))
goto out;
if (folio_test_large(folio)) {
if (split_huge_page(page))
goto out_unlock;
folio = page_folio(page);
}
/*
* 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, folio, &orig_pte) == 0) {
if (!kpage) {
/*
* While we hold folio lock, upgrade folio from
* anon to a NULL stable_node with the KSM flag set:
* stable_tree_insert() will update stable_node.
*/
folio_set_stable_node(folio, NULL);
folio_mark_accessed(folio);
/*
* Page reclaim just frees a clean folio with no dirty
* ptes: make sure that the ksm page would be swapped.
*/
if (!folio_test_dirty(folio))
folio_mark_dirty(folio);
err = 0;
} else if (pages_identical(page, kpage))
err = replace_page(vma, page, kpage, orig_pte);
}
out_unlock:
folio_unlock(folio);
out:
return err;
}
/*
* This function returns 0 if the pages were merged or if they are
* no longer merging candidates (e.g., VMA stale), -EFAULT otherwise.
*/
static int try_to_merge_with_zero_page(struct ksm_rmap_item *rmap_item,
struct page *page)
{
struct mm_struct *mm = rmap_item->mm;
int err = -EFAULT;
/*
* 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 && (rmap_item->oldchecksum == 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);
}
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 folio *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_folio(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 folio *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 folio *folio, *tree_folio = NULL;
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.
*
* ksm_get_folio 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.
*/
folio = ksm_get_folio(dup, KSM_GET_FOLIO_NOLOCK);
if (!folio)
continue;
/* Pick the best candidate if possible. */
if (!found || (is_page_sharing_candidate(dup) &&
(!is_page_sharing_candidate(found) ||
dup->rmap_hlist_len > found_rmap_hlist_len))) {
if (found)
folio_put(tree_folio);
found = dup;
found_rmap_hlist_len = found->rmap_hlist_len;
tree_folio = folio;
/* skip put_page for found candidate */
if (!prune_stale_stable_nodes &&
is_page_sharing_candidate(found))
break;
continue;
}
folio_put(folio);
}
if (found) {
if (hlist_is_singular_node(&found->hlist_dup, &stable_node->hlist)) {
/*
* 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);
}
} else {
/* Its hlist must be empty if no one found. */
free_stable_node_chain(stable_node, root);
}
*_stable_node_dup = found;
return tree_folio;
}
/*
* Like for ksm_get_folio, 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 folio *__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)) {
*_stable_node_dup = stable_node;
return ksm_get_folio(stable_node, KSM_GET_FOLIO_NOLOCK);
}
return stable_node_dup(_stable_node_dup, _stable_node, root,
prune_stale_stable_nodes);
}
static __always_inline struct folio *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 folio *chain(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, false);
}
/*
* 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,
* -EBUSY if the stable node's page is being migrated, NULL otherwise.
*/
static struct folio *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;
struct ksm_stable_node *page_node;
struct folio *folio;
folio = page_folio(page);
page_node = folio_stable_node(folio);
if (page_node && page_node->head != &migrate_nodes) {
/* ksm page forked */
folio_get(folio);
return folio;
}
nid = get_kpfn_nid(folio_pfn(folio));
root = root_stable_tree + nid;
again:
new = &root->rb_node;
parent = NULL;
while (*new) {
struct folio *tree_folio;
int ret;
cond_resched();
stable_node = rb_entry(*new, struct ksm_stable_node, node);
tree_folio = chain_prune(&stable_node_dup, &stable_node, root);
if (!tree_folio) {
/*
* If we walked over a stale stable_node,
* ksm_get_folio() 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_folio->page);
folio_put(tree_folio);
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);
/*
* If the mapcount of our migrated KSM folio is
* at most 1, we can merge it with another
* KSM folio where we know that we have space
* for one more mapping without exceeding the
* ksm_max_page_sharing limit: see
* chain_prune(). This way, we can avoid adding
* this stable node to the chain.
*/
if (folio_mapcount(folio) > 1)
goto chain_append;
}
if (!is_page_sharing_candidate(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_folio = ksm_get_folio(stable_node_dup,
KSM_GET_FOLIO_TRYLOCK);
if (PTR_ERR(tree_folio) == -EBUSY)
return ERR_PTR(-EBUSY);
if (unlikely(!tree_folio))
/*
* The tree may have been rebalanced,
* so re-evaluate parent and new.
*/
goto again;
folio_unlock(tree_folio);
if (get_kpfn_nid(stable_node_dup->kpfn) !=
NUMA(stable_node_dup->nid)) {
folio_put(tree_folio);
goto replace;
}
return tree_folio;
}
}
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)) {
folio_get(folio);
return folio;
} 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))
folio_get(folio);
else
folio = NULL;
} else {
rb_erase(&stable_node_dup->node, root);
folio = 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))
folio_get(folio);
else
folio = NULL;
} else {
folio = NULL;
}
}
stable_node_dup->head = &migrate_nodes;
list_add(&stable_node_dup->list, stable_node_dup->head);
return folio;
chain_append:
/*
* 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 folio *kfolio)
{
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;
bool need_chain = false;
kpfn = folio_pfn(kfolio);
nid = get_kpfn_nid(kpfn);
root = root_stable_tree + nid;
again:
parent = NULL;
new = &root->rb_node;
while (*new) {
struct folio *tree_folio;
int ret;
cond_resched();
stable_node = rb_entry(*new, struct ksm_stable_node, node);
tree_folio = chain(&stable_node_dup, &stable_node, root);
if (!tree_folio) {
/*
* If we walked over a stale stable_node,
* ksm_get_folio() 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(&kfolio->page, &tree_folio->page);
folio_put(tree_folio);
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;
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);
}
folio_set_stable_node(kfolio, stable_node_dup);
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 ksm_rmap_item *tree_rmap_item;
struct page *tree_page = NULL;
struct ksm_stable_node *stable_node;
struct folio *kfolio;
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;
} else {
remove_rmap_item_from_tree(rmap_item);
/*
* 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;
}
if (!try_to_merge_with_zero_page(rmap_item, page))
return;
}
/* Start by searching for the folio in the stable tree */
kfolio = stable_tree_search(page);
if (&kfolio->page == page && rmap_item->head == stable_node) {
folio_put(kfolio);
return;
}
remove_rmap_item_from_tree(rmap_item);
if (kfolio) {
if (kfolio == ERR_PTR(-EBUSY))
return;
err = try_to_merge_with_ksm_page(rmap_item, page, &kfolio->page);
if (!err) {
/*
* The page was successfully merged:
* add its rmap_item to the stable tree.
*/
folio_lock(kfolio);
stable_tree_append(rmap_item, folio_stable_node(kfolio),
max_page_sharing_bypass);
folio_unlock(kfolio);
}
folio_put(kfolio);
return;
}
tree_rmap_item =
unstable_tree_search_insert(rmap_item, page, &tree_page);
if (tree_rmap_item) {
bool split;
kfolio = 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 (kfolio) {
/*
* The pages were successfully merged: insert new
* node in the stable tree and add both rmap_items.
*/
folio_lock(kfolio);
stable_node = stable_tree_insert(kfolio);
if (stable_node) {
stable_tree_append(tree_rmap_item, stable_node,
false);
stable_tree_append(rmap_item, stable_node,
false);
}
folio_unlock(kfolio);
/*
* 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.
*
* @folio: folio containing the page to check
* @rmap_item: associated rmap_item of page
*/
static bool should_skip_rmap_item(struct folio *folio,
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 (folio_test_ksm(folio))
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) {
advisor_start_scan();
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 folio *folio;
list_for_each_entry_safe(stable_node, next,
&migrate_nodes, list) {
folio = ksm_get_folio(stable_node,
KSM_GET_FOLIO_NOLOCK);
if (folio)
folio_put(folio);
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) {
struct page *tmp_page = NULL;
struct folio_walk fw;
struct folio *folio;
if (ksm_test_exit(mm))
break;
folio = folio_walk_start(&fw, vma, ksm_scan.address, 0);
if (folio) {
if (!folio_is_zone_device(folio) &&
folio_test_anon(folio)) {
folio_get(folio);
tmp_page = fw.page;
}
folio_walk_end(&fw, vma);
}
if (tmp_page) {
flush_anon_page(vma, tmp_page, ksm_scan.address);
flush_dcache_page(tmp_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(folio, rmap_item)) {
folio_put(folio);
goto next_page;
}
ksm_scan.address += PAGE_SIZE;
*page = tmp_page;
} else {
folio_put(folio);
}
mmap_read_unlock(mm);
return rmap_item;
}
next_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;
advisor_stop_scan();
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;
while (scan_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++;
}
}
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);
if (ksmd_should_run()) {
sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs);
wait_event_freezable_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 bool __ksm_should_add_vma(const struct file *file, vm_flags_t vm_flags)
{
if (vm_flags & VM_MERGEABLE)
return false;
return ksm_compatible(file, vm_flags);
}
static void __ksm_add_vma(struct vm_area_struct *vma)
{
if (__ksm_should_add_vma(vma->vm_file, vma->vm_flags))
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_vma_flags - Update VMA flags to mark as mergeable if compatible
*
* @mm: Proposed VMA's mm_struct
* @file: Proposed VMA's file-backed mapping, if any.
* @vm_flags: Proposed VMA"s flags.
*
* Returns: @vm_flags possibly updated to mark mergeable.
*/
vm_flags_t ksm_vma_flags(const struct mm_struct *mm, const struct file *file,
vm_flags_t vm_flags)
{
if (test_bit(MMF_VM_MERGE_ANY, &mm->flags) &&
__ksm_should_add_vma(file, vm_flags))
vm_flags |= VM_MERGEABLE;
return vm_flags;
}
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, vm_flags_t *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 folio *ksm_might_need_to_copy(struct folio *folio,
struct vm_area_struct *vma, unsigned long addr)
{
struct page *page = folio_page(folio, 0);
struct anon_vma *anon_vma = folio_anon_vma(folio);
struct folio *new_folio;
if (folio_test_large(folio))
return folio;
if (folio_test_ksm(folio)) {
if (folio_stable_node(folio) &&
!(ksm_run & KSM_RUN_UNMERGE))
return folio; /* no need to copy it */
} else if (!anon_vma) {
return folio; /* no need to copy it */
} else if (folio->index == linear_page_index(vma, addr) &&
anon_vma->root == vma->anon_vma->root) {
return folio; /* still no need to copy it */
}
if (PageHWPoison(page))
return ERR_PTR(-EHWPOISON);
if (!folio_test_uptodate(folio))
return folio; /* let do_swap_page report the error */
new_folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, addr);
if (new_folio &&
mem_cgroup_charge(new_folio, vma->vm_mm, GFP_KERNEL)) {
folio_put(new_folio);
new_folio = NULL;
}
if (new_folio) {
if (copy_mc_user_highpage(folio_page(new_folio, 0), page,
addr, vma)) {
folio_put(new_folio);
return ERR_PTR(-EHWPOISON);
}
folio_set_dirty(new_folio);
__folio_mark_uptodate(new_folio);
__folio_set_locked(new_folio);
#ifdef CONFIG_SWAP
count_vm_event(KSM_SWPIN_COPY);
#endif
}
return new_folio;
}
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(const struct folio *folio, const struct page *page,
struct list_head *to_kill, int force_early)
{
struct ksm_stable_node *stable_node;
struct ksm_rmap_item *rmap_item;
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 ksm_get_folio() before it can see that folio->mapping
* has gone stale (or that the swapcache flag has been cleared).
*/
smp_wmb();
folio_set_stable_node(folio, 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 ksm_get_folio, 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 ksm_get_folio() 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
/*
* The process is mergeable only if any VMA is currently
* applicable to KSM.
*
* The mmap lock must be held in read mode.
*/
bool ksm_process_mergeable(struct mm_struct *mm)
{
struct vm_area_struct *vma;
mmap_assert_locked(mm);
VMA_ITERATOR(vmi, mm, 0);
for_each_vma(vmi, vma)
if (vma->vm_flags & VM_MERGEABLE)
return true;
return false;
}
long ksm_process_profit(struct mm_struct *mm)
{
return (long)(mm->ksm_merging_pages + mm_ksm_zero_pages(mm)) * 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;
if (ksm_advisor != KSM_ADVISOR_NONE)
return -EINVAL;
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", atomic_long_read(&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 + atomic_long_read(&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 ssize_t advisor_mode_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
const char *output;
if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
output = "none [scan-time]";
else
output = "[none] scan-time";
return sysfs_emit(buf, "%s\n", output);
}
static ssize_t advisor_mode_store(struct kobject *kobj,
struct kobj_attribute *attr, const char *buf,
size_t count)
{
enum ksm_advisor_type curr_advisor = ksm_advisor;
if (sysfs_streq("scan-time", buf))
ksm_advisor = KSM_ADVISOR_SCAN_TIME;
else if (sysfs_streq("none", buf))
ksm_advisor = KSM_ADVISOR_NONE;
else
return -EINVAL;
/* Set advisor default values */
if (curr_advisor != ksm_advisor)
set_advisor_defaults();
return count;
}
KSM_ATTR(advisor_mode);
static ssize_t advisor_max_cpu_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%u\n", ksm_advisor_max_cpu);
}
static ssize_t advisor_max_cpu_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
unsigned long value;
err = kstrtoul(buf, 10, &value);
if (err)
return -EINVAL;
ksm_advisor_max_cpu = value;
return count;
}
KSM_ATTR(advisor_max_cpu);
static ssize_t advisor_min_pages_to_scan_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%lu\n", ksm_advisor_min_pages_to_scan);
}
static ssize_t advisor_min_pages_to_scan_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
unsigned long value;
err = kstrtoul(buf, 10, &value);
if (err)
return -EINVAL;
ksm_advisor_min_pages_to_scan = value;
return count;
}
KSM_ATTR(advisor_min_pages_to_scan);
static ssize_t advisor_max_pages_to_scan_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%lu\n", ksm_advisor_max_pages_to_scan);
}
static ssize_t advisor_max_pages_to_scan_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
unsigned long value;
err = kstrtoul(buf, 10, &value);
if (err)
return -EINVAL;
ksm_advisor_max_pages_to_scan = value;
return count;
}
KSM_ATTR(advisor_max_pages_to_scan);
static ssize_t advisor_target_scan_time_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%lu\n", ksm_advisor_target_scan_time);
}
static ssize_t advisor_target_scan_time_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
int err;
unsigned long value;
err = kstrtoul(buf, 10, &value);
if (err)
return -EINVAL;
if (value < 1)
return -EINVAL;
ksm_advisor_target_scan_time = value;
return count;
}
KSM_ATTR(advisor_target_scan_time);
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,
&advisor_mode_attr.attr,
&advisor_max_cpu_attr.attr,
&advisor_min_pages_to_scan_attr.attr,
&advisor_max_pages_to_scan_attr.attr,
&advisor_target_scan_time_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);