| // 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 vma_ksm_compatible(struct vm_area_struct *vma) |
| { |
| if (vma->vm_flags & (VM_SHARED | VM_MAYSHARE | VM_PFNMAP | |
| VM_IO | VM_DONTEXPAND | VM_HUGETLB | |
| VM_MIXEDMAP| VM_DROPPABLE)) |
| return false; /* just ignore the advice */ |
| |
| if (vma_is_dax(vma)) |
| return false; |
| |
| #ifdef VM_SAO |
| if (vma->vm_flags & VM_SAO) |
| return false; |
| #endif |
| #ifdef VM_SPARC_ADI |
| if (vma->vm_flags & VM_SPARC_ADI) |
| return false; |
| #endif |
| |
| return true; |
| } |
| |
| static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm, |
| unsigned long addr) |
| { |
| struct vm_area_struct *vma; |
| if (ksm_test_exit(mm)) |
| return NULL; |
| vma = vma_lookup(mm, addr); |
| if (!vma || !(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) |
| return NULL; |
| return vma; |
| } |
| |
| static void break_cow(struct ksm_rmap_item *rmap_item) |
| { |
| struct mm_struct *mm = rmap_item->mm; |
| unsigned long addr = rmap_item->address; |
| struct vm_area_struct *vma; |
| |
| /* |
| * It is not an accident that whenever we want to break COW |
| * to undo, we also need to drop a reference to the anon_vma. |
| */ |
| put_anon_vma(rmap_item->anon_vma); |
| |
| mmap_read_lock(mm); |
| vma = find_mergeable_vma(mm, addr); |
| if (vma) |
| break_ksm(vma, addr, false); |
| mmap_read_unlock(mm); |
| } |
| |
| static struct page *get_mergeable_page(struct ksm_rmap_item *rmap_item) |
| { |
| struct mm_struct *mm = rmap_item->mm; |
| unsigned long addr = rmap_item->address; |
| struct vm_area_struct *vma; |
| struct page *page = 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 | |
| PAGE_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 | PAGE_MAPPING_KSM); |
| } |
| |
| #ifdef CONFIG_SYSFS |
| /* |
| * Only called through the sysfs control interface: |
| */ |
| static int remove_stable_node(struct ksm_stable_node *stable_node) |
| { |
| struct 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; |
| |
| anon_exclusive = PageAnonExclusive(&folio->page); |
| entry = ptep_get(pvmw.pte); |
| 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 void __ksm_add_vma(struct vm_area_struct *vma) |
| { |
| unsigned long vm_flags = vma->vm_flags; |
| |
| if (vm_flags & VM_MERGEABLE) |
| return; |
| |
| if (vma_ksm_compatible(vma)) |
| vm_flags_set(vma, VM_MERGEABLE); |
| } |
| |
| static int __ksm_del_vma(struct vm_area_struct *vma) |
| { |
| int err; |
| |
| if (!(vma->vm_flags & VM_MERGEABLE)) |
| return 0; |
| |
| if (vma->anon_vma) { |
| err = unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end, true); |
| if (err) |
| return err; |
| } |
| |
| vm_flags_clear(vma, VM_MERGEABLE); |
| return 0; |
| } |
| /** |
| * ksm_add_vma - Mark vma as mergeable if compatible |
| * |
| * @vma: Pointer to vma |
| */ |
| void ksm_add_vma(struct vm_area_struct *vma) |
| { |
| struct mm_struct *mm = vma->vm_mm; |
| |
| if (test_bit(MMF_VM_MERGE_ANY, &mm->flags)) |
| __ksm_add_vma(vma); |
| } |
| |
| static void ksm_add_vmas(struct mm_struct *mm) |
| { |
| struct vm_area_struct *vma; |
| |
| VMA_ITERATOR(vmi, mm, 0); |
| for_each_vma(vmi, vma) |
| __ksm_add_vma(vma); |
| } |
| |
| static int ksm_del_vmas(struct mm_struct *mm) |
| { |
| struct vm_area_struct *vma; |
| int err; |
| |
| VMA_ITERATOR(vmi, mm, 0); |
| for_each_vma(vmi, vma) { |
| err = __ksm_del_vma(vma); |
| if (err) |
| return err; |
| } |
| return 0; |
| } |
| |
| /** |
| * ksm_enable_merge_any - Add mm to mm ksm list and enable merging on all |
| * compatible VMA's |
| * |
| * @mm: Pointer to mm |
| * |
| * Returns 0 on success, otherwise error code |
| */ |
| int ksm_enable_merge_any(struct mm_struct *mm) |
| { |
| int err; |
| |
| if (test_bit(MMF_VM_MERGE_ANY, &mm->flags)) |
| return 0; |
| |
| if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) { |
| err = __ksm_enter(mm); |
| if (err) |
| return err; |
| } |
| |
| set_bit(MMF_VM_MERGE_ANY, &mm->flags); |
| ksm_add_vmas(mm); |
| |
| return 0; |
| } |
| |
| /** |
| * ksm_disable_merge_any - Disable merging on all compatible VMA's of the mm, |
| * previously enabled via ksm_enable_merge_any(). |
| * |
| * Disabling merging implies unmerging any merged pages, like setting |
| * MADV_UNMERGEABLE would. If unmerging fails, the whole operation fails and |
| * merging on all compatible VMA's remains enabled. |
| * |
| * @mm: Pointer to mm |
| * |
| * Returns 0 on success, otherwise error code |
| */ |
| int ksm_disable_merge_any(struct mm_struct *mm) |
| { |
| int err; |
| |
| if (!test_bit(MMF_VM_MERGE_ANY, &mm->flags)) |
| return 0; |
| |
| err = ksm_del_vmas(mm); |
| if (err) { |
| ksm_add_vmas(mm); |
| return err; |
| } |
| |
| clear_bit(MMF_VM_MERGE_ANY, &mm->flags); |
| return 0; |
| } |
| |
| int ksm_disable(struct mm_struct *mm) |
| { |
| mmap_assert_write_locked(mm); |
| |
| if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) |
| return 0; |
| if (test_bit(MMF_VM_MERGE_ANY, &mm->flags)) |
| return ksm_disable_merge_any(mm); |
| return ksm_del_vmas(mm); |
| } |
| |
| int ksm_madvise(struct vm_area_struct *vma, unsigned long start, |
| unsigned long end, int advice, unsigned long *vm_flags) |
| { |
| struct mm_struct *mm = vma->vm_mm; |
| int err; |
| |
| switch (advice) { |
| case MADV_MERGEABLE: |
| if (vma->vm_flags & VM_MERGEABLE) |
| return 0; |
| if (!vma_ksm_compatible(vma)) |
| return 0; |
| |
| if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) { |
| err = __ksm_enter(mm); |
| if (err) |
| return err; |
| } |
| |
| *vm_flags |= VM_MERGEABLE; |
| break; |
| |
| case MADV_UNMERGEABLE: |
| if (!(*vm_flags & VM_MERGEABLE)) |
| return 0; /* just ignore the advice */ |
| |
| if (vma->anon_vma) { |
| err = unmerge_ksm_pages(vma, start, end, true); |
| if (err) |
| return err; |
| } |
| |
| *vm_flags &= ~VM_MERGEABLE; |
| break; |
| } |
| |
| return 0; |
| } |
| EXPORT_SYMBOL_GPL(ksm_madvise); |
| |
| int __ksm_enter(struct mm_struct *mm) |
| { |
| struct ksm_mm_slot *mm_slot; |
| struct mm_slot *slot; |
| int needs_wakeup; |
| |
| mm_slot = mm_slot_alloc(mm_slot_cache); |
| if (!mm_slot) |
| return -ENOMEM; |
| |
| slot = &mm_slot->slot; |
| |
| /* Check ksm_run too? Would need tighter locking */ |
| needs_wakeup = list_empty(&ksm_mm_head.slot.mm_node); |
| |
| spin_lock(&ksm_mmlist_lock); |
| mm_slot_insert(mm_slots_hash, mm, slot); |
| /* |
| * When KSM_RUN_MERGE (or KSM_RUN_STOP), |
| * insert just behind the scanning cursor, to let the area settle |
| * down a little; when fork is followed by immediate exec, we don't |
| * want ksmd to waste time setting up and tearing down an rmap_list. |
| * |
| * But when KSM_RUN_UNMERGE, it's important to insert ahead of its |
| * scanning cursor, otherwise KSM pages in newly forked mms will be |
| * missed: then we might as well insert at the end of the list. |
| */ |
| if (ksm_run & KSM_RUN_UNMERGE) |
| list_add_tail(&slot->mm_node, &ksm_mm_head.slot.mm_node); |
| else |
| list_add_tail(&slot->mm_node, &ksm_scan.mm_slot->slot.mm_node); |
| spin_unlock(&ksm_mmlist_lock); |
| |
| set_bit(MMF_VM_MERGEABLE, &mm->flags); |
| mmgrab(mm); |
| |
| if (needs_wakeup) |
| wake_up_interruptible(&ksm_thread_wait); |
| |
| trace_ksm_enter(mm); |
| return 0; |
| } |
| |
| void __ksm_exit(struct mm_struct *mm) |
| { |
| struct ksm_mm_slot *mm_slot; |
| struct mm_slot *slot; |
| int easy_to_free = 0; |
| |
| /* |
| * This process is exiting: if it's straightforward (as is the |
| * case when ksmd was never running), free mm_slot immediately. |
| * But if it's at the cursor or has rmap_items linked to it, use |
| * mmap_lock to synchronize with any break_cows before pagetables |
| * are freed, and leave the mm_slot on the list for ksmd to free. |
| * Beware: ksm may already have noticed it exiting and freed the slot. |
| */ |
| |
| spin_lock(&ksm_mmlist_lock); |
| slot = mm_slot_lookup(mm_slots_hash, mm); |
| mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot); |
| if (mm_slot && ksm_scan.mm_slot != mm_slot) { |
| if (!mm_slot->rmap_list) { |
| hash_del(&slot->hash); |
| list_del(&slot->mm_node); |
| easy_to_free = 1; |
| } else { |
| list_move(&slot->mm_node, |
| &ksm_scan.mm_slot->slot.mm_node); |
| } |
| } |
| spin_unlock(&ksm_mmlist_lock); |
| |
| if (easy_to_free) { |
| mm_slot_free(mm_slot_cache, mm_slot); |
| clear_bit(MMF_VM_MERGE_ANY, &mm->flags); |
| clear_bit(MMF_VM_MERGEABLE, &mm->flags); |
| mmdrop(mm); |
| } else if (mm_slot) { |
| mmap_write_lock(mm); |
| mmap_write_unlock(mm); |
| } |
| |
| trace_ksm_exit(mm); |
| } |
| |
| struct 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 |
| 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); |
| } |
| |
|