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Diffstat (limited to 'mm/ksm.c')
| -rw-r--r-- | mm/ksm.c | 3188 |
1 files changed, 3188 insertions, 0 deletions
diff --git a/mm/ksm.c b/mm/ksm.c new file mode 100644 index 000000000..87a541ab1 --- /dev/null +++ b/mm/ksm.c @@ -0,0 +1,3188 @@ +/* + * Memory merging support. + * + * This code enables dynamic sharing of identical pages found in different + * memory areas, even if they are not shared by fork() + * + * Copyright (C) 2008-2009 Red Hat, Inc. + * Authors: + * Izik Eidus + * Andrea Arcangeli + * Chris Wright + * Hugh Dickins + * + * This work is licensed under the terms of the GNU GPL, version 2. + */ + +#include <linux/errno.h> +#include <linux/mm.h> +#include <linux/fs.h> +#include <linux/mman.h> +#include <linux/sched.h> +#include <linux/sched/mm.h> +#include <linux/sched/coredump.h> +#include <linux/rwsem.h> +#include <linux/pagemap.h> +#include <linux/rmap.h> +#include <linux/spinlock.h> +#include <linux/jhash.h> +#include <linux/delay.h> +#include <linux/kthread.h> +#include <linux/wait.h> +#include <linux/slab.h> +#include <linux/rbtree.h> +#include <linux/memory.h> +#include <linux/mmu_notifier.h> +#include <linux/swap.h> +#include <linux/ksm.h> +#include <linux/hashtable.h> +#include <linux/freezer.h> +#include <linux/oom.h> +#include <linux/numa.h> + +#include <asm/tlbflush.h> +#include "internal.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 + +/** + * 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 :c:type:`struct 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 mm_slot - ksm information per mm that is being scanned + * @link: link to the mm_slots hash list + * @mm_list: link into the mm_slots list, rooted in ksm_mm_head + * @rmap_list: head for this mm_slot's singly-linked list of rmap_items + * @mm: the mm that this information is valid for + */ +struct mm_slot { + struct hlist_node link; + struct list_head mm_list; + struct rmap_item *rmap_list; + struct mm_struct *mm; +}; + +/** + * struct ksm_scan - cursor for scanning + * @mm_slot: the current mm_slot we are scanning + * @address: the next address inside that to be scanned + * @rmap_list: link to the next rmap to be scanned in the rmap_list + * @seqnr: count of completed full scans (needed when removing unstable node) + * + * There is only the one ksm_scan instance of this cursor structure. + */ +struct ksm_scan { + struct mm_slot *mm_slot; + unsigned long address; + struct rmap_item **rmap_list; + unsigned long seqnr; +}; + +/** + * struct stable_node - node of the stable rbtree + * @node: rb node of this ksm page in the stable tree + * @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 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 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 + */ +struct rmap_item { + struct 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 */ + union { + struct rb_node node; /* when node of unstable tree */ + struct { /* when listed from stable tree */ + struct stable_node *head; + struct hlist_node hlist; + }; + }; +}; + +#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */ +#define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */ +#define STABLE_FLAG 0x200 /* is listed from the stable tree */ +#define KSM_FLAG_MASK (SEQNR_MASK|UNSTABLE_FLAG|STABLE_FLAG) + /* to mask all the flags */ + +/* 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 mm_slot ksm_mm_head = { + .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list), +}; +static struct ksm_scan ksm_scan = { + .mm_slot = &ksm_mm_head, +}; + +static struct kmem_cache *rmap_item_cache; +static struct kmem_cache *stable_node_cache; +static struct kmem_cache *mm_slot_cache; + +/* The number of nodes in the stable tree */ +static unsigned long ksm_pages_shared; + +/* The number of page slots additionally sharing those nodes */ +static unsigned long ksm_pages_sharing; + +/* The number of nodes in the unstable tree */ +static unsigned long ksm_pages_unshared; + +/* The number of rmap_items in use: to calculate pages_volatile */ +static unsigned long ksm_rmap_items; + +/* 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 int ksm_stable_node_chains_prune_millisecs = 2000; + +/* Maximum number of page slots sharing a stable node */ +static int ksm_max_page_sharing = 256; + +/* Number of pages ksmd should scan in one batch */ +static unsigned int ksm_thread_pages_to_scan = 100; + +/* Milliseconds ksmd should sleep between batches */ +static unsigned int ksm_thread_sleep_millisecs = 20; + +/* Checksum of an empty (zeroed) page */ +static unsigned int zero_checksum __read_mostly; + +/* Whether to merge empty (zeroed) pages with actual zero pages */ +static bool ksm_use_zero_pages __read_mostly; + +#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 DEFINE_MUTEX(ksm_thread_mutex); +static DEFINE_SPINLOCK(ksm_mmlist_lock); + +#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\ + sizeof(struct __struct), __alignof__(struct __struct),\ + (__flags), NULL) + +static int __init ksm_slab_init(void) +{ + rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0); + if (!rmap_item_cache) + goto out; + + stable_node_cache = KSM_KMEM_CACHE(stable_node, 0); + if (!stable_node_cache) + goto out_free1; + + mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0); + if (!mm_slot_cache) + goto out_free2; + + return 0; + +out_free2: + kmem_cache_destroy(stable_node_cache); +out_free1: + kmem_cache_destroy(rmap_item_cache); +out: + return -ENOMEM; +} + +static void __init ksm_slab_free(void) +{ + kmem_cache_destroy(mm_slot_cache); + kmem_cache_destroy(stable_node_cache); + kmem_cache_destroy(rmap_item_cache); + mm_slot_cache = NULL; +} + +static __always_inline bool is_stable_node_chain(struct stable_node *chain) +{ + return chain->rmap_hlist_len == STABLE_NODE_CHAIN; +} + +static __always_inline bool is_stable_node_dup(struct stable_node *dup) +{ + return dup->head == STABLE_NODE_DUP_HEAD; +} + +static inline void stable_node_chain_add_dup(struct stable_node *dup, + struct 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 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 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 rmap_item *alloc_rmap_item(void) +{ + struct 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 rmap_item *rmap_item) +{ + ksm_rmap_items--; + rmap_item->mm = NULL; /* debug safety */ + kmem_cache_free(rmap_item_cache, rmap_item); +} + +static inline struct stable_node *alloc_stable_node(void) +{ + /* + * 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 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); +} + +static inline struct mm_slot *alloc_mm_slot(void) +{ + if (!mm_slot_cache) /* initialization failed */ + return NULL; + return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL); +} + +static inline void free_mm_slot(struct mm_slot *mm_slot) +{ + kmem_cache_free(mm_slot_cache, mm_slot); +} + +static struct mm_slot *get_mm_slot(struct mm_struct *mm) +{ + struct mm_slot *slot; + + hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm) + if (slot->mm == mm) + return slot; + + return NULL; +} + +static void insert_to_mm_slots_hash(struct mm_struct *mm, + struct mm_slot *mm_slot) +{ + mm_slot->mm = mm; + hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm); +} + +/* + * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's + * page tables after it has passed through ksm_exit() - which, if necessary, + * takes mmap_sem briefly to serialize against them. ksm_exit() does not set + * a special flag: they can just back out as soon as mm_users goes to zero. + * ksm_test_exit() is used throughout to make this test for exit: in some + * places for correctness, in some places just to avoid unnecessary work. + */ +static inline bool ksm_test_exit(struct mm_struct *mm) +{ + return atomic_read(&mm->mm_users) == 0; +} + +/* + * We use break_ksm to break COW on a ksm page: it's a stripped down + * + * if (get_user_pages(addr, 1, 1, 1, &page, NULL) == 1) + * put_page(page); + * + * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma, + * in case the application has unmapped and remapped mm,addr meanwhile. + * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP + * mmap of /dev/mem or /dev/kmem, where we would not want to touch it. + * + * FAULT_FLAG/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) +{ + struct page *page; + vm_fault_t ret = 0; + + do { + cond_resched(); + page = follow_page(vma, addr, + FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE); + if (IS_ERR_OR_NULL(page)) + break; + if (PageKsm(page)) + ret = handle_mm_fault(vma, addr, + FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE); + else + ret = VM_FAULT_WRITE; + put_page(page); + } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM))); + /* + * We must loop because handle_mm_fault() may back out if there's + * any difficulty e.g. if pte accessed bit gets updated concurrently. + * + * VM_FAULT_WRITE is what we have been hoping for: it indicates that + * COW has been broken, even if the vma does not permit VM_WRITE; + * but note that a concurrent fault might break PageKsm for us. + * + * VM_FAULT_SIGBUS could occur if we race with truncation of the + * backing file, which also invalidates anonymous pages: that's + * okay, that truncation will have unmapped the PageKsm for us. + * + * VM_FAULT_OOM: at the time of writing (late July 2009), setting + * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the + * current task has TIF_MEMDIE set, and will be OOM killed on return + * to user; and ksmd, having no mm, would never be chosen for that. + * + * But if the mm is in a limited mem_cgroup, then the fault may fail + * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and + * even ksmd can fail in this way - though it's usually breaking ksm + * just to undo a merge it made a moment before, so unlikely to oom. + * + * That's a pity: we might therefore have more kernel pages allocated + * than we're counting as nodes in the stable tree; but ksm_do_scan + * will retry to break_cow on each pass, so should recover the page + * in due course. The important thing is to not let VM_MERGEABLE + * be cleared while any such pages might remain in the area. + */ + return (ret & VM_FAULT_OOM) ? -ENOMEM : 0; +} + +static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm, + unsigned long addr) +{ + struct vm_area_struct *vma; + if (ksm_test_exit(mm)) + return NULL; + vma = find_vma(mm, addr); + if (!vma || vma->vm_start > addr) + return NULL; + if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) + return NULL; + return vma; +} + +static void break_cow(struct rmap_item *rmap_item) +{ + struct mm_struct *mm = rmap_item->mm; + unsigned long addr = rmap_item->address; + struct vm_area_struct *vma; + + /* + * It is not an accident that whenever we want to break COW + * to undo, we also need to drop a reference to the anon_vma. + */ + put_anon_vma(rmap_item->anon_vma); + + down_read(&mm->mmap_sem); + vma = find_mergeable_vma(mm, addr); + if (vma) + break_ksm(vma, addr); + up_read(&mm->mmap_sem); +} + +static struct page *get_mergeable_page(struct rmap_item *rmap_item) +{ + struct mm_struct *mm = rmap_item->mm; + unsigned long addr = rmap_item->address; + struct vm_area_struct *vma; + struct page *page; + + down_read(&mm->mmap_sem); + vma = find_mergeable_vma(mm, addr); + if (!vma) + goto out; + + page = follow_page(vma, addr, FOLL_GET); + if (IS_ERR_OR_NULL(page)) + goto out; + if (PageAnon(page)) { + flush_anon_page(vma, page, addr); + flush_dcache_page(page); + } else { + put_page(page); +out: + page = NULL; + } + up_read(&mm->mmap_sem); + return page; +} + +/* + * 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 stable_node *alloc_stable_node_chain(struct stable_node *dup, + struct rb_root *root) +{ + struct 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 = -1; /* 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 wrprotected and have the exact same + * content. + */ + stable_node_chain_add_dup(dup, chain); + } + return chain; +} + +static inline void free_stable_node_chain(struct 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 stable_node *stable_node) +{ + struct 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--; + else + ksm_pages_shared--; + 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. + */ +#if defined(GCC_VERSION) && GCC_VERSION >= 40903 + BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes); + BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1); +#endif + + if (stable_node->head == &migrate_nodes) + list_del(&stable_node->list); + else + stable_node_dup_del(stable_node); + free_stable_node(stable_node); +} + +/* + * get_ksm_page: checks if the page indicated by the stable node + * is still its ksm page, despite having held no reference to it. + * In which case we can trust the content of the page, and it + * returns the gotten page; but if the page has now been zapped, + * remove the stale node from the stable tree and return NULL. + * But beware, the stable node's page might be being migrated. + * + * You would expect the stable_node to hold a reference to the ksm page. + * But if it increments the page's count, swapping out has to wait for + * ksmd to come around again before it can free the page, which may take + * seconds or even minutes: much too unresponsive. So instead we use a + * "keyhole reference": access to the ksm page from the stable node peeps + * out through its keyhole to see if that page still holds the right key, + * pointing back to this stable node. This relies on freeing a PageAnon + * page to reset its page->mapping to NULL, and relies on no other use of + * a page to put something that might look like our key in page->mapping. + * is on its way to being freed; but it is an anomaly to bear in mind. + */ +static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it) +{ + struct page *page; + void *expected_mapping; + unsigned long kpfn; + + expected_mapping = (void *)((unsigned long)stable_node | + PAGE_MAPPING_KSM); +again: + kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */ + page = pfn_to_page(kpfn); + if (READ_ONCE(page->mapping) != expected_mapping) + goto stale; + + /* + * We cannot do anything with the page while its refcount is 0. + * Usually 0 means free, or tail of a higher-order page: in which + * case this node is no longer referenced, and should be freed; + * however, it might mean that the page is under page_ref_freeze(). + * The __remove_mapping() case is easy, again the node is now stale; + * but if page is swapcache in migrate_page_move_mapping(), it might + * still be our page, in which case it's essential to keep the node. + */ + while (!get_page_unless_zero(page)) { + /* + * Another check for page->mapping != expected_mapping would + * work here too. We have chosen the !PageSwapCache test to + * optimize the common case, when the page is or is about to + * be freed: PageSwapCache is cleared (under spin_lock_irq) + * in the ref_freeze section of __remove_mapping(); but Anon + * page->mapping reset to NULL later, in free_pages_prepare(). + */ + if (!PageSwapCache(page)) + goto stale; + cpu_relax(); + } + + if (READ_ONCE(page->mapping) != expected_mapping) { + put_page(page); + goto stale; + } + + if (lock_it) { + lock_page(page); + if (READ_ONCE(page->mapping) != expected_mapping) { + unlock_page(page); + put_page(page); + goto stale; + } + } + return page; + +stale: + /* + * We come here from above when page->mapping or !PageSwapCache + * suggests that the node is stale; but it might be under migration. + * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(), + * 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 rmap_item *rmap_item) +{ + if (rmap_item->address & STABLE_FLAG) { + struct stable_node *stable_node; + struct page *page; + + stable_node = rmap_item->head; + page = get_ksm_page(stable_node, true); + if (!page) + goto out; + + hlist_del(&rmap_item->hlist); + unlock_page(page); + put_page(page); + + if (!hlist_empty(&stable_node->hlist)) + ksm_pages_sharing--; + else + ksm_pages_shared--; + 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 mm_slot *mm_slot, + struct rmap_item **rmap_list) +{ + while (*rmap_list) { + struct rmap_item *rmap_item = *rmap_list; + *rmap_list = rmap_item->rmap_list; + remove_rmap_item_from_tree(rmap_item); + free_rmap_item(rmap_item); + } +} + +/* + * Though it's very tempting to unmerge 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_sem. Nor does it fit with the way we skip dup'ing + * rmap_items from parent to child at fork time (so as not to waste time + * if exit comes before the next scan reaches it). + * + * Similarly, although we'd like to remove rmap_items (so updating counts + * and freeing memory) when unmerging an area, it's easier to leave that + * to the next pass of ksmd - consider, for example, how ksmd might be + * in cmp_and_merge_page on one of the rmap_items we would be removing. + */ +static int unmerge_ksm_pages(struct vm_area_struct *vma, + unsigned long start, unsigned long end) +{ + unsigned long addr; + int err = 0; + + for (addr = start; addr < end && !err; addr += PAGE_SIZE) { + if (ksm_test_exit(vma->vm_mm)) + break; + if (signal_pending(current)) + err = -ERESTARTSYS; + else + err = break_ksm(vma, addr); + } + return err; +} + +static inline struct stable_node *page_stable_node(struct page *page) +{ + return PageKsm(page) ? page_rmapping(page) : NULL; +} + +static inline void set_page_stable_node(struct page *page, + struct stable_node *stable_node) +{ + page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM); +} + +#ifdef CONFIG_SYSFS +/* + * Only called through the sysfs control interface: + */ +static int remove_stable_node(struct stable_node *stable_node) +{ + struct page *page; + int err; + + page = get_ksm_page(stable_node, true); + if (!page) { + /* + * get_ksm_page did remove_node_from_stable_tree itself. + */ + return 0; + } + + /* + * Page could be still mapped if this races with __mmput() running in + * between ksm_exit() and exit_mmap(). Just refuse to let + * merge_across_nodes/max_page_sharing be switched. + */ + err = -EBUSY; + if (!page_mapped(page)) { + /* + * The stable node did not yet appear stale to get_ksm_page(), + * since that allows for an unmapped ksm page to be recognized + * right up until it is freed; but the node is safe to remove. + * This page might be in a pagevec waiting to be freed, + * or it might be PageSwapCache (perhaps under writeback), + * or it might have been removed from swapcache a moment ago. + */ + set_page_stable_node(page, NULL); + remove_node_from_stable_tree(stable_node); + err = 0; + } + + unlock_page(page); + put_page(page); + return err; +} + +static int remove_stable_node_chain(struct stable_node *stable_node, + struct rb_root *root) +{ + struct 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 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 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 mm_slot *mm_slot; + struct mm_struct *mm; + struct vm_area_struct *vma; + int err = 0; + + spin_lock(&ksm_mmlist_lock); + ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next, + struct mm_slot, mm_list); + spin_unlock(&ksm_mmlist_lock); + + for (mm_slot = ksm_scan.mm_slot; + mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) { + mm = mm_slot->mm; + down_read(&mm->mmap_sem); + for (vma = mm->mmap; vma; vma = vma->vm_next) { + if (ksm_test_exit(mm)) + break; + if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) + continue; + err = unmerge_ksm_pages(vma, + vma->vm_start, vma->vm_end); + if (err) + goto error; + } + + remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list); + up_read(&mm->mmap_sem); + + spin_lock(&ksm_mmlist_lock); + ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next, + struct mm_slot, mm_list); + if (ksm_test_exit(mm)) { + hash_del(&mm_slot->link); + list_del(&mm_slot->mm_list); + spin_unlock(&ksm_mmlist_lock); + + free_mm_slot(mm_slot); + clear_bit(MMF_VM_MERGEABLE, &mm->flags); + 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: + up_read(&mm->mmap_sem); + spin_lock(&ksm_mmlist_lock); + ksm_scan.mm_slot = &ksm_mm_head; + spin_unlock(&ksm_mmlist_lock); + return err; +} +#endif /* CONFIG_SYSFS */ + +static u32 calc_checksum(struct page *page) +{ + u32 checksum; + void *addr = kmap_atomic(page); + checksum = jhash2(addr, PAGE_SIZE / 4, 17); + kunmap_atomic(addr); + return checksum; +} + +static int memcmp_pages(struct page *page1, struct page *page2) +{ + char *addr1, *addr2; + int ret; + + addr1 = kmap_atomic(page1); + addr2 = kmap_atomic(page2); + ret = memcmp(addr1, addr2, PAGE_SIZE); + kunmap_atomic(addr2); + kunmap_atomic(addr1); + return ret; +} + +static inline int pages_identical(struct page *page1, struct page *page2) +{ + return !memcmp_pages(page1, page2); +} + +static int write_protect_page(struct vm_area_struct *vma, struct page *page, + pte_t *orig_pte) +{ + struct mm_struct *mm = vma->vm_mm; + struct page_vma_mapped_walk pvmw = { + .page = page, + .vma = vma, + }; + int swapped; + int err = -EFAULT; + unsigned long mmun_start; /* For mmu_notifiers */ + unsigned long mmun_end; /* For mmu_notifiers */ + + pvmw.address = page_address_in_vma(page, vma); + if (pvmw.address == -EFAULT) + goto out; + + BUG_ON(PageTransCompound(page)); + + mmun_start = pvmw.address; + mmun_end = pvmw.address + PAGE_SIZE; + mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end); + + if (!page_vma_mapped_walk(&pvmw)) + goto out_mn; + if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?")) + goto out_unlock; + + if (pte_write(*pvmw.pte) || pte_dirty(*pvmw.pte) || + (pte_protnone(*pvmw.pte) && pte_savedwrite(*pvmw.pte)) || + mm_tlb_flush_pending(mm)) { + pte_t entry; + + swapped = PageSwapCache(page); + flush_cache_page(vma, pvmw.address, page_to_pfn(page)); + /* + * Ok this is tricky, when get_user_pages_fast() run it doesn't + * take any lock, therefore the check that we are going to make + * with the pagecount against the mapcount is racey and + * O_DIRECT can happen right after the check. + * So we clear the pte and flush the tlb before the check + * this assure us that no O_DIRECT can happen after the check + * or in the middle of the check. + * + * No need to notify as we are downgrading page table to read + * only not changing it to point to a new page. + * + * See Documentation/vm/mmu_notifier.rst + */ + entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte); + /* + * Check that no O_DIRECT or similar I/O is in progress on the + * page + */ + if (page_mapcount(page) + 1 + swapped != page_count(page)) { + set_pte_at(mm, pvmw.address, pvmw.pte, entry); + goto out_unlock; + } + if (pte_dirty(entry)) + set_page_dirty(page); + + if (pte_protnone(entry)) + entry = pte_mkclean(pte_clear_savedwrite(entry)); + else + entry = pte_mkclean(pte_wrprotect(entry)); + set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry); + } + *orig_pte = *pvmw.pte; + err = 0; + +out_unlock: + page_vma_mapped_walk_done(&pvmw); +out_mn: + mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end); +out: + return err; +} + +/** + * replace_page - replace page in vma by new ksm page + * @vma: vma that holds the pte pointing to page + * @page: the page we are replacing by kpage + * @kpage: the ksm page we replace page by + * @orig_pte: the original value of the pte + * + * Returns 0 on success, -EFAULT on failure. + */ +static int replace_page(struct vm_area_struct *vma, struct page *page, + struct page *kpage, pte_t orig_pte) +{ + struct mm_struct *mm = vma->vm_mm; + pmd_t *pmd; + pte_t *ptep; + pte_t newpte; + spinlock_t *ptl; + unsigned long addr; + int err = -EFAULT; + unsigned long mmun_start; /* For mmu_notifiers */ + unsigned long mmun_end; /* For mmu_notifiers */ + + addr = page_address_in_vma(page, vma); + if (addr == -EFAULT) + goto out; + + pmd = mm_find_pmd(mm, addr); + if (!pmd) + goto out; + + mmun_start = addr; + mmun_end = addr + PAGE_SIZE; + mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end); + + ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); + if (!pte_same(*ptep, orig_pte)) { + pte_unmap_unlock(ptep, ptl); + goto out_mn; + } + + /* + * No need to check ksm_use_zero_pages here: we can only have a + * zero_page here if ksm_use_zero_pages was enabled alreaady. + */ + if (!is_zero_pfn(page_to_pfn(kpage))) { + get_page(kpage); + page_add_anon_rmap(kpage, vma, addr, false); + newpte = mk_pte(kpage, vma->vm_page_prot); + } else { + newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage), + vma->vm_page_prot)); + /* + * 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)); + /* + * No need to notify as we are replacing a read only page with another + * read only page with the same content. + * + * See Documentation/vm/mmu_notifier.rst + */ + ptep_clear_flush(vma, addr, ptep); + set_pte_at_notify(mm, addr, ptep, newpte); + + page_remove_rmap(page, false); + if (!page_mapped(page)) + try_to_free_swap(page); + put_page(page); + + pte_unmap_unlock(ptep, ptl); + err = 0; +out_mn: + mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end); +out: + return err; +} + +/* + * try_to_merge_one_page - take two pages and merge them into one + * @vma: the vma that holds the pte pointing to page + * @page: the PageAnon page that we want to replace with kpage + * @kpage: the PageKsm page that we want to map instead of page, + * or NULL the first time when we want to use page as kpage. + * + * This function returns 0 if the pages were merged, -EFAULT otherwise. + */ +static int try_to_merge_one_page(struct vm_area_struct *vma, + struct page *page, struct page *kpage) +{ + pte_t orig_pte = __pte(0); + int err = -EFAULT; + + if (page == kpage) /* ksm page forked */ + return 0; + + if (!PageAnon(page)) + goto out; + + /* + * We need the page lock to read a stable PageSwapCache in + * write_protect_page(). We use trylock_page() instead of + * lock_page() because we don't want to wait here - we + * prefer to continue scanning and merging different pages, + * then come back to this page when it is unlocked. + */ + if (!trylock_page(page)) + goto out; + + if (PageTransCompound(page)) { + if (split_huge_page(page)) + goto out_unlock; + } + + /* + * If this anonymous page is mapped only here, its pte may need + * to be write-protected. If it's mapped elsewhere, all of its + * ptes are necessarily already write-protected. But in either + * case, we need to lock and check page_count is not raised. + */ + if (write_protect_page(vma, page, &orig_pte) == 0) { + if (!kpage) { + /* + * While we hold page lock, upgrade page from + * PageAnon+anon_vma to PageKsm+NULL stable_node: + * stable_tree_insert() will update stable_node. + */ + set_page_stable_node(page, NULL); + mark_page_accessed(page); + /* + * Page reclaim just frees a clean page with no dirty + * ptes: make sure that the ksm page would be swapped. + */ + if (!PageDirty(page)) + SetPageDirty(page); + err = 0; + } else if (pages_identical(page, kpage)) + err = replace_page(vma, page, kpage, orig_pte); + } + + if ((vma->vm_flags & VM_LOCKED) && kpage && !err) { + munlock_vma_page(page); + if (!PageMlocked(kpage)) { + unlock_page(page); + lock_page(kpage); + mlock_vma_page(kpage); + page = kpage; /* for final unlock */ + } + } + +out_unlock: + unlock_page(page); +out: + return err; +} + +/* + * try_to_merge_with_ksm_page - like try_to_merge_two_pages, + * but no new kernel page is allocated: kpage must already be a ksm page. + * + * This function returns 0 if the pages were merged, -EFAULT otherwise. + */ +static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item, + struct page *page, struct page *kpage) +{ + struct mm_struct *mm = rmap_item->mm; + struct vm_area_struct *vma; + int err = -EFAULT; + + down_read(&mm->mmap_sem); + 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_sem */ + rmap_item->anon_vma = vma->anon_vma; + get_anon_vma(vma->anon_vma); +out: + up_read(&mm->mmap_sem); + return err; +} + +/* + * try_to_merge_two_pages - take two identical pages and prepare them + * to be merged into one page. + * + * This function returns the kpage if we successfully merged two identical + * pages into one ksm page, NULL otherwise. + * + * Note that this function upgrades page to ksm page: if one of the pages + * is already a ksm page, try_to_merge_with_ksm_page should be used. + */ +static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item, + struct page *page, + struct rmap_item *tree_rmap_item, + struct page *tree_page) +{ + int err; + + err = try_to_merge_with_ksm_page(rmap_item, page, NULL); + if (!err) { + err = try_to_merge_with_ksm_page(tree_rmap_item, + tree_page, page); + /* + * If that fails, we have a ksm page with only one pte + * pointing to it: so break it. + */ + if (err) + break_cow(rmap_item); + } + return err ? NULL : page; +} + +static __always_inline +bool __is_page_sharing_candidate(struct 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 stable_node *stable_node) +{ + return __is_page_sharing_candidate(stable_node, 0); +} + +static struct page *stable_node_dup(struct stable_node **_stable_node_dup, + struct stable_node **_stable_node, + struct rb_root *root, + bool prune_stale_stable_nodes) +{ + struct stable_node *dup, *found = NULL, *stable_node = *_stable_node; + struct hlist_node *hlist_safe; + struct page *_tree_page, *tree_page = NULL; + int nr = 0; + int found_rmap_hlist_len; + + if (!prune_stale_stable_nodes || + time_before(jiffies, stable_node->chain_prune_time + + msecs_to_jiffies( + ksm_stable_node_chains_prune_millisecs))) + prune_stale_stable_nodes = false; + else + stable_node->chain_prune_time = jiffies; + + hlist_for_each_entry_safe(dup, hlist_safe, + &stable_node->hlist, hlist_dup) { + cond_resched(); + /* + * We must walk all stable_node_dup to prune the stale + * stable nodes during lookup. + * + * get_ksm_page can drop the nodes from the + * stable_node->hlist if they point to freed pages + * (that's why we do a _safe walk). The "dup" + * stable_node parameter itself will be freed from + * under us if it returns NULL. + */ + _tree_page = get_ksm_page(dup, false); + if (!_tree_page) + continue; + nr += 1; + if (is_page_sharing_candidate(dup)) { + if (!found || + dup->rmap_hlist_len > found_rmap_hlist_len) { + if (found) + put_page(tree_page); + found = dup; + found_rmap_hlist_len = found->rmap_hlist_len; + tree_page = _tree_page; + + /* skip put_page for found dup */ + if (!prune_stale_stable_nodes) + break; + continue; + } + } + put_page(_tree_page); + } + + if (found) { + /* + * nr is counting all dups in the chain only if + * prune_stale_stable_nodes is true, otherwise we may + * break the loop at nr == 1 even if there are + * multiple entries. + */ + if (prune_stale_stable_nodes && nr == 1) { + /* + * If there's not just one entry it would + * corrupt memory, better BUG_ON. In KSM + * context with no lock held it's not even + * fatal. + */ + BUG_ON(stable_node->hlist.first->next); + + /* + * There's just one entry and it is below the + * deduplication limit so drop the chain. + */ + rb_replace_node(&stable_node->node, &found->node, + root); + free_stable_node(stable_node); + ksm_stable_node_chains--; + ksm_stable_node_dups--; + /* + * NOTE: the caller depends on the stable_node + * to be equal to stable_node_dup if the chain + * was collapsed. + */ + *_stable_node = found; + /* + * Just for robustneess as stable_node is + * otherwise left as a stable pointer, the + * compiler shall optimize it away at build + * time. + */ + stable_node = NULL; + } else if (stable_node->hlist.first != &found->hlist_dup && + __is_page_sharing_candidate(found, 1)) { + /* + * If the found stable_node dup can accept one + * more future merge (in addition to the one + * that is underway) and is not at the head of + * the chain, put it there so next search will + * be quicker in the !prune_stale_stable_nodes + * case. + * + * NOTE: it would be inaccurate to use nr > 1 + * instead of checking the hlist.first pointer + * directly, because in the + * prune_stale_stable_nodes case "nr" isn't + * the position of the found dup in the chain, + * but the total number of dups in the chain. + */ + hlist_del(&found->hlist_dup); + hlist_add_head(&found->hlist_dup, + &stable_node->hlist); + } + } + + *_stable_node_dup = found; + return tree_page; +} + +static struct stable_node *stable_node_dup_any(struct stable_node *stable_node, + struct rb_root *root) +{ + if (!is_stable_node_chain(stable_node)) + return stable_node; + if (hlist_empty(&stable_node->hlist)) { + free_stable_node_chain(stable_node, root); + return NULL; + } + return hlist_entry(stable_node->hlist.first, + typeof(*stable_node), hlist_dup); +} + +/* + * Like for get_ksm_page, this function can free the *_stable_node and + * *_stable_node_dup if the returned tree_page is NULL. + * + * It can also free and overwrite *_stable_node with the found + * stable_node_dup if the chain is collapsed (in which case + * *_stable_node will be equal to *_stable_node_dup like if the chain + * never existed). It's up to the caller to verify tree_page is not + * NULL before dereferencing *_stable_node or *_stable_node_dup. + * + * *_stable_node_dup is really a second output parameter of this + * function and will be overwritten in all cases, the caller doesn't + * need to initialize it. + */ +static struct page *__stable_node_chain(struct stable_node **_stable_node_dup, + struct stable_node **_stable_node, + struct rb_root *root, + bool prune_stale_stable_nodes) +{ + struct stable_node *stable_node = *_stable_node; + if (!is_stable_node_chain(stable_node)) { + if (is_page_sharing_candidate(stable_node)) { + *_stable_node_dup = stable_node; + return get_ksm_page(stable_node, false); + } + /* + * _stable_node_dup set to NULL means the stable_node + * reached the ksm_max_page_sharing limit. + */ + *_stable_node_dup = NULL; + return NULL; + } + return stable_node_dup(_stable_node_dup, _stable_node, root, + prune_stale_stable_nodes); +} + +static __always_inline struct page *chain_prune(struct stable_node **s_n_d, + struct stable_node **s_n, + struct rb_root *root) +{ + return __stable_node_chain(s_n_d, s_n, root, true); +} + +static __always_inline struct page *chain(struct stable_node **s_n_d, + struct stable_node *s_n, + struct rb_root *root) +{ + struct stable_node *old_stable_node = s_n; + struct page *tree_page; + + tree_page = __stable_node_chain(s_n_d, &s_n, root, false); + /* not pruning dups so s_n cannot have changed */ + VM_BUG_ON(s_n != old_stable_node); + return tree_page; +} + +/* + * stable_tree_search - search for page inside the stable tree + * + * This function checks if there is a page inside the stable tree + * with identical content to the page that we are scanning right now. + * + * This function returns the stable tree node of identical content if found, + * NULL otherwise. + */ +static struct page *stable_tree_search(struct page *page) +{ + int nid; + struct rb_root *root; + struct rb_node **new; + struct rb_node *parent; + struct stable_node *stable_node, *stable_node_dup, *stable_node_any; + struct stable_node *page_node; + + page_node = page_stable_node(page); + if (page_node && page_node->head != &migrate_nodes) { + /* ksm page forked */ + get_page(page); + return page; + } + + nid = get_kpfn_nid(page_to_pfn(page)); + root = root_stable_tree + nid; +again: + new = &root->rb_node; + parent = NULL; + + while (*new) { + struct page *tree_page; + int ret; + + cond_resched(); + stable_node = rb_entry(*new, struct stable_node, node); + stable_node_any = NULL; + tree_page = chain_prune(&stable_node_dup, &stable_node, root); + /* + * NOTE: stable_node may have been freed by + * chain_prune() if the returned stable_node_dup is + * not NULL. stable_node_dup may have been inserted in + * the rbtree instead as a regular stable_node (in + * order to collapse the stable_node chain if a single + * stable_node dup was found in it). In such case the + * stable_node is overwritten by the calleee to point + * to the stable_node_dup that was collapsed in the + * stable rbtree and stable_node will be equal to + * stable_node_dup like if the chain never existed. + */ + if (!stable_node_dup) { + /* + * Either all stable_node dups were full in + * this stable_node chain, or this chain was + * empty and should be rb_erased. + */ + stable_node_any = stable_node_dup_any(stable_node, + root); + if (!stable_node_any) { + /* rb_erase just run */ + goto again; + } + /* + * Take any of the stable_node dups page of + * this stable_node chain to let the tree walk + * continue. All KSM pages belonging to the + * stable_node dups in a stable_node chain + * have the same content and they're + * wrprotected at all times. Any will work + * fine to continue the walk. + */ + tree_page = get_ksm_page(stable_node_any, false); + } + VM_BUG_ON(!stable_node_dup ^ !!stable_node_any); + if (!tree_page) { + /* + * If we walked over a stale stable_node, + * get_ksm_page() will call rb_erase() and it + * may rebalance the tree from under us. So + * restart the search from scratch. Returning + * NULL would be safe too, but we'd generate + * false negative insertions just because some + * stable_node was stale. + */ + goto again; + } + + ret = memcmp_pages(page, tree_page); + put_page(tree_page); + + parent = *new; + if (ret < 0) + new = &parent->rb_left; + else if (ret > 0) + new = &parent->rb_right; + else { + if (page_node) { + VM_BUG_ON(page_node->head != &migrate_nodes); + /* + * Test if the migrated page should be merged + * into a stable node dup. If the mapcount is + * 1 we can migrate it with another KSM page + * without adding it to the chain. + */ + if (page_mapcount(page) > 1) + goto chain_append; + } + + if (!stable_node_dup) { + /* + * If the stable_node is a chain and + * we got a payload match in memcmp + * but we cannot merge the scanned + * page in any of the existing + * stable_node dups because they're + * all full, we need to wait the + * scanned page to find itself a match + * in the unstable tree to create a + * brand new KSM page to add later to + * the dups of this stable_node. + */ + return NULL; + } + + /* + * Lock and unlock the stable_node's page (which + * might already have been migrated) so that page + * migration is sure to notice its raised count. + * It would be more elegant to return stable_node + * than kpage, but that involves more changes. + */ + tree_page = get_ksm_page(stable_node_dup, true); + if (unlikely(!tree_page)) + /* + * The tree may have been rebalanced, + * so re-evaluate parent and new. + */ + goto again; + unlock_page(tree_page); + + if (get_kpfn_nid(stable_node_dup->kpfn) != + NUMA(stable_node_dup->nid)) { + put_page(tree_page); + goto replace; + } + return tree_page; + } + } + + if (!page_node) + return NULL; + + list_del(&page_node->list); + DO_NUMA(page_node->nid = nid); + rb_link_node(&page_node->node, parent, new); + rb_insert_color(&page_node->node, root); +out: + if (is_page_sharing_candidate(page_node)) { + get_page(page); + return page; + } else + return NULL; + +replace: + /* + * If stable_node was a chain and chain_prune collapsed it, + * stable_node has been updated to be the new regular + * stable_node. A collapse of the chain is indistinguishable + * from the case there was no chain in the stable + * rbtree. Otherwise stable_node is the chain and + * stable_node_dup is the dup to replace. + */ + if (stable_node_dup == stable_node) { + VM_BUG_ON(is_stable_node_chain(stable_node_dup)); + VM_BUG_ON(is_stable_node_dup(stable_node_dup)); + /* there is no chain */ + if (page_node) { + VM_BUG_ON(page_node->head != &migrate_nodes); + list_del(&page_node->list); + DO_NUMA(page_node->nid = nid); + rb_replace_node(&stable_node_dup->node, + &page_node->node, + root); + if (is_page_sharing_candidate(page_node)) + get_page(page); + else + page = NULL; + } else { + rb_erase(&stable_node_dup->node, root); + page = NULL; + } + } else { + VM_BUG_ON(!is_stable_node_chain(stable_node)); + __stable_node_dup_del(stable_node_dup); + if (page_node) { + VM_BUG_ON(page_node->head != &migrate_nodes); + list_del(&page_node->list); + DO_NUMA(page_node->nid = nid); + stable_node_chain_add_dup(page_node, stable_node); + if (is_page_sharing_candidate(page_node)) + get_page(page); + else + page = NULL; + } else { + page = NULL; + } + } + stable_node_dup->head = &migrate_nodes; + list_add(&stable_node_dup->list, stable_node_dup->head); + return page; + +chain_append: + /* stable_node_dup could be null if it reached the limit */ + if (!stable_node_dup) + stable_node_dup = stable_node_any; + /* + * If stable_node was a chain and chain_prune collapsed it, + * stable_node has been updated to be the new regular + * stable_node. A collapse of the chain is indistinguishable + * from the case there was no chain in the stable + * rbtree. Otherwise stable_node is the chain and + * stable_node_dup is the dup to replace. + */ + if (stable_node_dup == stable_node) { + VM_BUG_ON(is_stable_node_chain(stable_node_dup)); + 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_chain(stable_node)); + 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 stable_node *stable_tree_insert(struct page *kpage) +{ + int nid; + unsigned long kpfn; + struct rb_root *root; + struct rb_node **new; + struct rb_node *parent; + struct stable_node *stable_node, *stable_node_dup, *stable_node_any; + bool need_chain = false; + + kpfn = page_to_pfn(kpage); + nid = get_kpfn_nid(kpfn); + root = root_stable_tree + nid; +again: + parent = NULL; + new = &root->rb_node; + + while (*new) { + struct page *tree_page; + int ret; + + cond_resched(); + stable_node = rb_entry(*new, struct stable_node, node); + stable_node_any = NULL; + tree_page = chain(&stable_node_dup, stable_node, root); + if (!stable_node_dup) { + /* + * Either all stable_node dups were full in + * this stable_node chain, or this chain was + * empty and should be rb_erased. + */ + stable_node_any = stable_node_dup_any(stable_node, + root); + if (!stable_node_any) { + /* rb_erase just run */ + goto again; + } + /* + * Take any of the stable_node dups page of + * this stable_node chain to let the tree walk + * continue. All KSM pages belonging to the + * stable_node dups in a stable_node chain + * have the same content and they're + * wrprotected at all times. Any will work + * fine to continue the walk. + */ + tree_page = get_ksm_page(stable_node_any, false); + } + VM_BUG_ON(!stable_node_dup ^ !!stable_node_any); + if (!tree_page) { + /* + * If we walked over a stale stable_node, + * get_ksm_page() will call rb_erase() and it + * may rebalance the tree from under us. So + * restart the search from scratch. Returning + * NULL would be safe too, but we'd generate + * false negative insertions just because some + * stable_node was stale. + */ + goto again; + } + + ret = memcmp_pages(kpage, tree_page); + put_page(tree_page); + + parent = *new; + if (ret < 0) + new = &parent->rb_left; + else if (ret > 0) + new = &parent->rb_right; + else { + need_chain = true; + break; + } + } + + stable_node_dup = alloc_stable_node(); + if (!stable_node_dup) + return NULL; + + INIT_HLIST_HEAD(&stable_node_dup->hlist); + stable_node_dup->kpfn = kpfn; + set_page_stable_node(kpage, stable_node_dup); + stable_node_dup->rmap_hlist_len = 0; + DO_NUMA(stable_node_dup->nid = nid); + if (!need_chain) { + rb_link_node(&stable_node_dup->node, parent, new); + rb_insert_color(&stable_node_dup->node, root); + } else { + if (!is_stable_node_chain(stable_node)) { + struct stable_node *orig = stable_node; + /* chain is missing so create it */ + stable_node = alloc_stable_node_chain(orig, root); + if (!stable_node) { + free_stable_node(stable_node_dup); + return NULL; + } + } + stable_node_chain_add_dup(stable_node_dup, stable_node); + } + + return stable_node_dup; +} + +/* + * unstable_tree_search_insert - search for identical page, + * else insert rmap_item into the unstable tree. + * + * This function searches for a page in the unstable tree identical to the + * page currently being scanned; and if no identical page is found in the + * tree, we insert rmap_item as a new object into the unstable tree. + * + * This function returns pointer to rmap_item found to be identical + * to the currently scanned page, NULL otherwise. + * + * This function does both searching and inserting, because they share + * the same walking algorithm in an rbtree. + */ +static +struct rmap_item *unstable_tree_search_insert(struct 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 rmap_item *tree_rmap_item; + struct page *tree_page; + int ret; + + cond_resched(); + tree_rmap_item = rb_entry(*new, struct rmap_item, node); + tree_page = get_mergeable_page(tree_rmap_item); + if (!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 rmap_item *rmap_item, + struct 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 undeflow 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++; +} + +/* + * cmp_and_merge_page - first see if page can be merged into the stable tree; + * if not, compare checksum to previous and if it's the same, see if page can + * be inserted into the unstable tree, or merged with a page already there and + * both transferred to the stable tree. + * + * @page: the page that we are searching identical page to. + * @rmap_item: the reverse mapping into the virtual address of this page + */ +static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) +{ + struct mm_struct *mm = rmap_item->mm; + struct rmap_item *tree_rmap_item; + struct page *tree_page = NULL; + struct stable_node *stable_node; + struct page *kpage; + unsigned int checksum; + int err; + bool max_page_sharing_bypass = false; + + stable_node = page_stable_node(page); + if (stable_node) { + if (stable_node->head != &migrate_nodes && + get_kpfn_nid(READ_ONCE(stable_node->kpfn)) != + NUMA(stable_node->nid)) { + stable_node_dup_del(stable_node); + stable_node->head = &migrate_nodes; + list_add(&stable_node->list, stable_node->head); + } + if (stable_node->head != &migrate_nodes && + rmap_item->head == stable_node) + return; + /* + * If it's a KSM fork, allow it to go over the sharing limit + * without warnings. + */ + if (!is_page_sharing_candidate(stable_node)) + max_page_sharing_bypass = true; + } + + /* We first start with searching the page inside the stable tree */ + kpage = stable_tree_search(page); + if (kpage == page && rmap_item->head == stable_node) { + put_page(kpage); + return; + } + + remove_rmap_item_from_tree(rmap_item); + + if (kpage) { + err = try_to_merge_with_ksm_page(rmap_item, page, kpage); + if (!err) { + /* + * The page was successfully merged: + * add its rmap_item to the stable tree. + */ + lock_page(kpage); + stable_tree_append(rmap_item, page_stable_node(kpage), + max_page_sharing_bypass); + unlock_page(kpage); + } + put_page(kpage); + return; + } + + /* + * If the hash value of the page has changed from the last time + * we calculated it, this page is changing frequently: therefore we + * don't want to insert it in the unstable tree, and we don't want + * to waste our time searching for something identical to it there. + */ + checksum = calc_checksum(page); + if (rmap_item->oldchecksum != checksum) { + rmap_item->oldchecksum = checksum; + return; + } + + /* + * Same checksum as an empty page. We attempt to merge it with the + * appropriate zero page if the user enabled this via sysfs. + */ + if (ksm_use_zero_pages && (checksum == zero_checksum)) { + struct vm_area_struct *vma; + + down_read(&mm->mmap_sem); + vma = find_mergeable_vma(mm, rmap_item->address); + if (vma) { + err = try_to_merge_one_page(vma, page, + ZERO_PAGE(rmap_item->address)); + } else { + /* + * If the vma is out of date, we do not need to + * continue. + */ + err = 0; + } + up_read(&mm->mmap_sem); + /* + * In case of failure, the page was not really empty, so we + * need to continue. Otherwise we're done. + */ + if (!err) + return; + } + tree_rmap_item = + unstable_tree_search_insert(rmap_item, page, &tree_page); + if (tree_rmap_item) { + bool split; + + kpage = try_to_merge_two_pages(rmap_item, page, + tree_rmap_item, tree_page); + /* + * If both pages we tried to merge belong to the same compound + * page, then we actually ended up increasing the reference + * count of the same compound page twice, and split_huge_page + * failed. + * Here we set a flag if that happened, and we use it later to + * try split_huge_page again. Since we call put_page right + * afterwards, the reference count will be correct and + * split_huge_page should succeed. + */ + split = PageTransCompound(page) + && compound_head(page) == compound_head(tree_page); + put_page(tree_page); + if (kpage) { + /* + * The pages were successfully merged: insert new + * node in the stable tree and add both rmap_items. + */ + lock_page(kpage); + stable_node = stable_tree_insert(kpage); + if (stable_node) { + stable_tree_append(tree_rmap_item, stable_node, + false); + stable_tree_append(rmap_item, stable_node, + false); + } + unlock_page(kpage); + + /* + * If we fail to insert the page into the stable tree, + * we will have 2 virtual addresses that are pointing + * to a ksm page left outside the stable tree, + * in which case we need to break_cow on both. + */ + if (!stable_node) { + break_cow(tree_rmap_item); + break_cow(rmap_item); + } + } else if (split) { + /* + * We are here if we tried to merge two pages and + * failed because they both belonged to the same + * compound page. We will split the page now, but no + * merging will take place. + * We do not want to add the cost of a full lock; if + * the page is locked, it is better to skip it and + * perhaps try again later. + */ + if (!trylock_page(page)) + return; + split_huge_page(page); + unlock_page(page); + } + } +} + +static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot, + struct rmap_item **rmap_list, + unsigned long addr) +{ + struct rmap_item *rmap_item; + + while (*rmap_list) { + rmap_item = *rmap_list; + if ((rmap_item->address & PAGE_MASK) == addr) + return rmap_item; + if (rmap_item->address > addr) + break; + *rmap_list = rmap_item->rmap_list; + remove_rmap_item_from_tree(rmap_item); + free_rmap_item(rmap_item); + } + + rmap_item = alloc_rmap_item(); + if (rmap_item) { + /* It has already been zeroed */ + rmap_item->mm = mm_slot->mm; + rmap_item->address = addr; + rmap_item->rmap_list = *rmap_list; + *rmap_list = rmap_item; + } + return rmap_item; +} + +static struct rmap_item *scan_get_next_rmap_item(struct page **page) +{ + struct mm_struct *mm; + struct mm_slot *slot; + struct vm_area_struct *vma; + struct rmap_item *rmap_item; + int nid; + + if (list_empty(&ksm_mm_head.mm_list)) + return NULL; + + slot = ksm_scan.mm_slot; + if (slot == &ksm_mm_head) { + /* + * A number of pages can hang around indefinitely on per-cpu + * pagevecs, raised page count preventing write_protect_page + * from merging them. Though it doesn't really matter much, + * it is puzzling to see some stuck in pages_volatile until + * other activity jostles them out, and they also prevented + * LTP's KSM test from succeeding deterministically; so drain + * them here (here rather than on entry to ksm_do_scan(), + * so we don't IPI too often when pages_to_scan is set low). + */ + lru_add_drain_all(); + + /* + * 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 stable_node *stable_node, *next; + struct page *page; + + list_for_each_entry_safe(stable_node, next, + &migrate_nodes, list) { + page = get_ksm_page(stable_node, false); + if (page) + put_page(page); + cond_resched(); + } + } + + for (nid = 0; nid < ksm_nr_node_ids; nid++) + root_unstable_tree[nid] = RB_ROOT; + + spin_lock(&ksm_mmlist_lock); + slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); + ksm_scan.mm_slot = slot; + spin_unlock(&ksm_mmlist_lock); + /* + * Although we tested list_empty() above, a racing __ksm_exit + * of the last mm on the list may have removed it since then. + */ + if (slot == &ksm_mm_head) + return NULL; +next_mm: + ksm_scan.address = 0; + ksm_scan.rmap_list = &slot->rmap_list; + } + + mm = slot->mm; + down_read(&mm->mmap_sem); + if (ksm_test_exit(mm)) + vma = NULL; + else + vma = find_vma(mm, ksm_scan.address); + + for (; vma; vma = vma->vm_next) { + if (!(vma->vm_flags & VM_MERGEABLE)) + continue; + if (ksm_scan.address < vma->vm_start) + ksm_scan.address = vma->vm_start; + if (!vma->anon_vma) + ksm_scan.address = vma->vm_end; + + while (ksm_scan.address < vma->vm_end) { + if (ksm_test_exit(mm)) + break; + *page = follow_page(vma, ksm_scan.address, FOLL_GET); + if (IS_ERR_OR_NULL(*page)) { + ksm_scan.address += PAGE_SIZE; + cond_resched(); + continue; + } + if (PageAnon(*page)) { + flush_anon_page(vma, *page, ksm_scan.address); + flush_dcache_page(*page); + rmap_item = get_next_rmap_item(slot, + ksm_scan.rmap_list, ksm_scan.address); + if (rmap_item) { + ksm_scan.rmap_list = + &rmap_item->rmap_list; + ksm_scan.address += PAGE_SIZE; + } else + put_page(*page); + up_read(&mm->mmap_sem); + return rmap_item; + } + put_page(*page); + ksm_scan.address += PAGE_SIZE; + cond_resched(); + } + } + + if (ksm_test_exit(mm)) { + ksm_scan.address = 0; + ksm_scan.rmap_list = &slot->rmap_list; + } + /* + * Nuke all the rmap_items that are above this current rmap: + * because there were no VM_MERGEABLE vmas with such addresses. + */ + remove_trailing_rmap_items(slot, ksm_scan.rmap_list); + + spin_lock(&ksm_mmlist_lock); + ksm_scan.mm_slot = list_entry(slot->mm_list.next, + struct mm_slot, mm_list); + if (ksm_scan.address == 0) { + /* + * We've completed a full scan of all vmas, holding mmap_sem + * throughout, and found no VM_MERGEABLE: so do the same as + * __ksm_exit does to remove this mm from all our lists now. + * This applies either when cleaning up after __ksm_exit + * (but beware: we can reach here even before __ksm_exit), + * or when all VM_MERGEABLE areas have been unmapped (and + * mmap_sem then protects against race with MADV_MERGEABLE). + */ + hash_del(&slot->link); + list_del(&slot->mm_list); + spin_unlock(&ksm_mmlist_lock); + + free_mm_slot(slot); + clear_bit(MMF_VM_MERGEABLE, &mm->flags); + up_read(&mm->mmap_sem); + mmdrop(mm); + } else { + up_read(&mm->mmap_sem); + /* + * up_read(&mm->mmap_sem) 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 */ + slot = ksm_scan.mm_slot; + if (slot != &ksm_mm_head) + goto next_mm; + + ksm_scan.seqnr++; + return NULL; +} + +/** + * ksm_do_scan - the ksm scanner main worker function. + * @scan_npages: number of pages we want to scan before we return. + */ +static void ksm_do_scan(unsigned int scan_npages) +{ + struct rmap_item *rmap_item; + struct page *uninitialized_var(page); + + while (scan_npages-- && likely(!freezing(current))) { + cond_resched(); + rmap_item = scan_get_next_rmap_item(&page); + if (!rmap_item) + return; + cmp_and_merge_page(page, rmap_item); + put_page(page); + } +} + +static int ksmd_should_run(void) +{ + return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list); +} + +static int ksm_scan_thread(void *nothing) +{ + set_freezable(); + set_user_nice(current, 5); + + while (!kthread_should_stop()) { + mutex_lock(&ksm_thread_mutex); + wait_while_offlining(); + if (ksmd_should_run()) + ksm_do_scan(ksm_thread_pages_to_scan); + mutex_unlock(&ksm_thread_mutex); + + try_to_freeze(); + + if (ksmd_should_run()) { + schedule_timeout_interruptible( + msecs_to_jiffies(ksm_thread_sleep_millisecs)); + } else { + wait_event_freezable(ksm_thread_wait, + ksmd_should_run() || kthread_should_stop()); + } + } + return 0; +} + +int ksm_madvise(struct vm_area_struct *vma, unsigned long start, + unsigned long end, int advice, unsigned long *vm_flags) +{ + struct mm_struct *mm = vma->vm_mm; + int err; + + switch (advice) { + case MADV_MERGEABLE: + /* + * Be somewhat over-protective for now! + */ + if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE | + VM_PFNMAP | VM_IO | VM_DONTEXPAND | + VM_HUGETLB | VM_MIXEDMAP)) + return 0; /* just ignore the advice */ + + if (vma_is_dax(vma)) + return 0; + +#ifdef VM_SAO + if (*vm_flags & VM_SAO) + return 0; +#endif +#ifdef VM_SPARC_ADI + if (*vm_flags & VM_SPARC_ADI) + return 0; +#endif + + if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) { + err = __ksm_enter(mm); + if (err) + return err; + } + + *vm_flags |= VM_MERGEABLE; + break; + + case MADV_UNMERGEABLE: + if (!(*vm_flags & VM_MERGEABLE)) + return 0; /* just ignore the advice */ + + if (vma->anon_vma) { + err = unmerge_ksm_pages(vma, start, end); + if (err) + return err; + } + + *vm_flags &= ~VM_MERGEABLE; + break; + } + + return 0; +} + +int __ksm_enter(struct mm_struct *mm) +{ + struct mm_slot *mm_slot; + int needs_wakeup; + + mm_slot = alloc_mm_slot(); + if (!mm_slot) + return -ENOMEM; + + /* Check ksm_run too? Would need tighter locking */ + needs_wakeup = list_empty(&ksm_mm_head.mm_list); + + spin_lock(&ksm_mmlist_lock); + insert_to_mm_slots_hash(mm, mm_slot); + /* + * 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(&mm_slot->mm_list, &ksm_mm_head.mm_list); + else + list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list); + spin_unlock(&ksm_mmlist_lock); + + set_bit(MMF_VM_MERGEABLE, &mm->flags); + mmgrab(mm); + + if (needs_wakeup) + wake_up_interruptible(&ksm_thread_wait); + + return 0; +} + +void __ksm_exit(struct mm_struct *mm) +{ + struct mm_slot *mm_slot; + int easy_to_free = 0; + + /* + * This process is exiting: if it's straightforward (as is the + * case when ksmd was never running), free mm_slot immediately. + * But if it's at the cursor or has rmap_items linked to it, use + * mmap_sem to synchronize with any break_cows before pagetables + * are freed, and leave the mm_slot on the list for ksmd to free. + * Beware: ksm may already have noticed it exiting and freed the slot. + */ + + spin_lock(&ksm_mmlist_lock); + mm_slot = get_mm_slot(mm); + if (mm_slot && ksm_scan.mm_slot != mm_slot) { + if (!mm_slot->rmap_list) { + hash_del(&mm_slot->link); + list_del(&mm_slot->mm_list); + easy_to_free = 1; + } else { + list_move(&mm_slot->mm_list, + &ksm_scan.mm_slot->mm_list); + } + } + spin_unlock(&ksm_mmlist_lock); + + if (easy_to_free) { + free_mm_slot(mm_slot); + clear_bit(MMF_VM_MERGEABLE, &mm->flags); + mmdrop(mm); + } else if (mm_slot) { + down_write(&mm->mmap_sem); + up_write(&mm->mmap_sem); + } +} + +struct page *ksm_might_need_to_copy(struct page *page, + struct vm_area_struct *vma, unsigned long address) +{ + struct anon_vma *anon_vma = page_anon_vma(page); + struct page *new_page; + + if (PageKsm(page)) { + if (page_stable_node(page) && + !(ksm_run & KSM_RUN_UNMERGE)) + return page; /* no need to copy it */ + } else if (!anon_vma) { + return page; /* no need to copy it */ + } else if (anon_vma->root == vma->anon_vma->root && + page->index == linear_page_index(vma, address)) { + return page; /* still no need to copy it */ + } + if (!PageUptodate(page)) + return page; /* let do_swap_page report the error */ + + new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address); + if (new_page) { + copy_user_highpage(new_page, page, address, vma); + + SetPageDirty(new_page); + __SetPageUptodate(new_page); + __SetPageLocked(new_page); + } + + return new_page; +} + +void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc) +{ + struct stable_node *stable_node; + struct rmap_item *rmap_item; + int search_new_forks = 0; + + VM_BUG_ON_PAGE(!PageKsm(page), page); + + /* + * Rely on the page lock to protect against concurrent modifications + * to that page's node of the stable tree. + */ + VM_BUG_ON_PAGE(!PageLocked(page), page); + + stable_node = page_stable_node(page); + 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(); + 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 & ~KSM_FLAG_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(page, vma, addr, rwc->arg)) { + anon_vma_unlock_read(anon_vma); + return; + } + if (rwc->done && rwc->done(page)) { + anon_vma_unlock_read(anon_vma); + return; + } + } + anon_vma_unlock_read(anon_vma); + } + if (!search_new_forks++) + goto again; +} + +#ifdef CONFIG_MIGRATION +void ksm_migrate_page(struct page *newpage, struct page *oldpage) +{ + struct stable_node *stable_node; + + VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage); + VM_BUG_ON_PAGE(!PageLocked(newpage), newpage); + VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage); + + stable_node = page_stable_node(newpage); + if (stable_node) { + VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage); + stable_node->kpfn = page_to_pfn(newpage); + /* + * newpage->mapping was set in advance; now we need smp_wmb() + * to make sure that the new stable_node->kpfn is visible + * to get_ksm_page() before it can see that oldpage->mapping + * has gone stale (or that PageSwapCache has been cleared). + */ + smp_wmb(); + set_page_stable_node(oldpage, 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 stable_node *stable_node, + unsigned long start_pfn, + unsigned long end_pfn) +{ + if (stable_node->kpfn >= start_pfn && + stable_node->kpfn < end_pfn) { + /* + * Don't get_ksm_page, page has already gone: + * which is why we keep kpfn instead of page* + */ + remove_node_from_stable_tree(stable_node); + return true; + } + return false; +} + +static bool stable_node_chain_remove_range(struct stable_node *stable_node, + unsigned long start_pfn, + unsigned long end_pfn, + struct rb_root *root) +{ + struct 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 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 stable_node, node); + if (stable_node_chain_remove_range(stable_node, + start_pfn, end_pfn, + root_stable_tree + + nid)) + node = rb_first(root_stable_tree + nid); + else + node = rb_next(node); + cond_resched(); + } + } + list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) { + if (stable_node->kpfn >= start_pfn && + stable_node->kpfn < end_pfn) + remove_node_from_stable_tree(stable_node); + cond_resched(); + } +} + +static int ksm_memory_callback(struct notifier_block *self, + unsigned long action, void *arg) +{ + struct memory_notify *mn = arg; + + switch (action) { + case MEM_GOING_OFFLINE: + /* + * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items() + * and remove_all_stable_nodes() while memory is going offline: + * it is unsafe for them to touch the stable tree at this time. + * But unmerge_ksm_pages(), rmap lookups and other entry points + * which do not need the ksm_thread_mutex are all safe. + */ + mutex_lock(&ksm_thread_mutex); + ksm_run |= KSM_RUN_OFFLINE; + mutex_unlock(&ksm_thread_mutex); + break; + + case MEM_OFFLINE: + /* + * Most of the work is done by page migration; but there might + * be a few stable_nodes left over, still pointing to struct + * pages which have been offlined: prune those from the tree, + * otherwise get_ksm_page() might later try to access a + * non-existent struct page. + */ + ksm_check_stable_tree(mn->start_pfn, + mn->start_pfn + mn->nr_pages); + /* fallthrough */ + + case MEM_CANCEL_OFFLINE: + mutex_lock(&ksm_thread_mutex); + ksm_run &= ~KSM_RUN_OFFLINE; + mutex_unlock(&ksm_thread_mutex); + + smp_mb(); /* wake_up_bit advises this */ + wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE)); + break; + } + return NOTIFY_OK; +} +#else +static void wait_while_offlining(void) +{ +} +#endif /* CONFIG_MEMORY_HOTREMOVE */ + +#ifdef CONFIG_SYSFS +/* + * This all compiles without CONFIG_SYSFS, but is a waste of space. + */ + +#define KSM_ATTR_RO(_name) \ + static struct kobj_attribute _name##_attr = __ATTR_RO(_name) +#define KSM_ATTR(_name) \ + static struct kobj_attribute _name##_attr = \ + __ATTR(_name, 0644, _name##_show, _name##_store) + +static ssize_t sleep_millisecs_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs); +} + +static ssize_t sleep_millisecs_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + unsigned long msecs; + int err; + + err = kstrtoul(buf, 10, &msecs); + if (err || msecs > UINT_MAX) + return -EINVAL; + + ksm_thread_sleep_millisecs = msecs; + + return count; +} +KSM_ATTR(sleep_millisecs); + +static ssize_t pages_to_scan_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%u\n", ksm_thread_pages_to_scan); +} + +static ssize_t pages_to_scan_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + unsigned long nr_pages; + + err = kstrtoul(buf, 10, &nr_pages); + if (err || nr_pages > UINT_MAX) + return -EINVAL; + + ksm_thread_pages_to_scan = nr_pages; + + return count; +} +KSM_ATTR(pages_to_scan); + +static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr, + char *buf) +{ + return sprintf(buf, "%lu\n", ksm_run); +} + +static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + unsigned long flags; + + err = kstrtoul(buf, 10, &flags); + if (err || flags > UINT_MAX) + return -EINVAL; + if (flags > KSM_RUN_UNMERGE) + return -EINVAL; + + /* + * KSM_RUN_MERGE sets ksmd running, and 0 stops it running. + * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items, + * breaking COW to free the pages_shared (but leaves mm_slots + * on the list for when ksmd may be set running again). + */ + + mutex_lock(&ksm_thread_mutex); + wait_while_offlining(); + if (ksm_run != flags) { + ksm_run = flags; + if (flags & KSM_RUN_UNMERGE) { + set_current_oom_origin(); + err = unmerge_and_remove_all_rmap_items(); + clear_current_oom_origin(); + if (err) { + ksm_run = KSM_RUN_STOP; + count = err; + } + } + } + mutex_unlock(&ksm_thread_mutex); + + if (flags & KSM_RUN_MERGE) + wake_up_interruptible(&ksm_thread_wait); + + return count; +} +KSM_ATTR(run); + +#ifdef CONFIG_NUMA +static ssize_t merge_across_nodes_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%u\n", ksm_merge_across_nodes); +} + +static ssize_t merge_across_nodes_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + unsigned long knob; + + err = kstrtoul(buf, 10, &knob); + if (err) + return err; + if (knob > 1) + return -EINVAL; + + mutex_lock(&ksm_thread_mutex); + wait_while_offlining(); + if (ksm_merge_across_nodes != knob) { + if (ksm_pages_shared || remove_all_stable_nodes()) + err = -EBUSY; + else if (root_stable_tree == one_stable_tree) { + struct rb_root *buf; + /* + * This is the first time that we switch away from the + * default of merging across nodes: must now allocate + * a buffer to hold as many roots as may be needed. + * Allocate stable and unstable together: + * MAXSMP NODES_SHIFT 10 will use 16kB. + */ + buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf), + GFP_KERNEL); + /* Let us assume that RB_ROOT is NULL is zero */ + if (!buf) + err = -ENOMEM; + else { + root_stable_tree = buf; + root_unstable_tree = buf + nr_node_ids; + /* Stable tree is empty but not the unstable */ + root_unstable_tree[0] = one_unstable_tree[0]; + } + } + if (!err) { + ksm_merge_across_nodes = knob; + ksm_nr_node_ids = knob ? 1 : nr_node_ids; + } + } + mutex_unlock(&ksm_thread_mutex); + + return err ? err : count; +} +KSM_ATTR(merge_across_nodes); +#endif + +static ssize_t use_zero_pages_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%u\n", ksm_use_zero_pages); +} +static ssize_t use_zero_pages_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + bool value; + + err = kstrtobool(buf, &value); + if (err) + return -EINVAL; + + ksm_use_zero_pages = value; + + return count; +} +KSM_ATTR(use_zero_pages); + +static ssize_t max_page_sharing_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%u\n", ksm_max_page_sharing); +} + +static ssize_t max_page_sharing_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + int knob; + + err = kstrtoint(buf, 10, &knob); + if (err) + return err; + /* + * When a KSM page is created it is shared by 2 mappings. This + * being a signed comparison, it implicitly verifies it's not + * negative. + */ + if (knob < 2) + return -EINVAL; + + if (READ_ONCE(ksm_max_page_sharing) == knob) + return count; + + mutex_lock(&ksm_thread_mutex); + wait_while_offlining(); + if (ksm_max_page_sharing != knob) { + if (ksm_pages_shared || remove_all_stable_nodes()) + err = -EBUSY; + else + ksm_max_page_sharing = knob; + } + mutex_unlock(&ksm_thread_mutex); + + return err ? err : count; +} +KSM_ATTR(max_page_sharing); + +static ssize_t pages_shared_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%lu\n", ksm_pages_shared); +} +KSM_ATTR_RO(pages_shared); + +static ssize_t pages_sharing_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%lu\n", ksm_pages_sharing); +} +KSM_ATTR_RO(pages_sharing); + +static ssize_t pages_unshared_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%lu\n", ksm_pages_unshared); +} +KSM_ATTR_RO(pages_unshared); + +static ssize_t pages_volatile_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + long ksm_pages_volatile; + + ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared + - ksm_pages_sharing - ksm_pages_unshared; + /* + * It was not worth any locking to calculate that statistic, + * but it might therefore sometimes be negative: conceal that. + */ + if (ksm_pages_volatile < 0) + ksm_pages_volatile = 0; + return sprintf(buf, "%ld\n", ksm_pages_volatile); +} +KSM_ATTR_RO(pages_volatile); + +static ssize_t stable_node_dups_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%lu\n", ksm_stable_node_dups); +} +KSM_ATTR_RO(stable_node_dups); + +static ssize_t stable_node_chains_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%lu\n", ksm_stable_node_chains); +} +KSM_ATTR_RO(stable_node_chains); + +static ssize_t +stable_node_chains_prune_millisecs_show(struct kobject *kobj, + struct kobj_attribute *attr, + char *buf) +{ + return sprintf(buf, "%u\n", ksm_stable_node_chains_prune_millisecs); +} + +static ssize_t +stable_node_chains_prune_millisecs_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + unsigned long msecs; + int err; + + err = kstrtoul(buf, 10, &msecs); + if (err || msecs > UINT_MAX) + return -EINVAL; + + ksm_stable_node_chains_prune_millisecs = msecs; + + return count; +} +KSM_ATTR(stable_node_chains_prune_millisecs); + +static ssize_t full_scans_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sprintf(buf, "%lu\n", ksm_scan.seqnr); +} +KSM_ATTR_RO(full_scans); + +static struct attribute *ksm_attrs[] = { + &sleep_millisecs_attr.attr, + &pages_to_scan_attr.attr, + &run_attr.attr, + &pages_shared_attr.attr, + &pages_sharing_attr.attr, + &pages_unshared_attr.attr, + &pages_volatile_attr.attr, + &full_scans_attr.attr, +#ifdef CONFIG_NUMA + &merge_across_nodes_attr.attr, +#endif + &max_page_sharing_attr.attr, + &stable_node_chains_attr.attr, + &stable_node_dups_attr.attr, + &stable_node_chains_prune_millisecs_attr.attr, + &use_zero_pages_attr.attr, + NULL, +}; + +static const struct attribute_group ksm_attr_group = { + .attrs = ksm_attrs, + .name = "ksm", +}; +#endif /* CONFIG_SYSFS */ + +static int __init ksm_init(void) +{ + struct task_struct *ksm_thread; + int err; + + /* The correct value depends on page size and endianness */ + zero_checksum = calc_checksum(ZERO_PAGE(0)); + /* Default to false for backwards compatibility */ + ksm_use_zero_pages = false; + + err = ksm_slab_init(); + if (err) + goto out; + + ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd"); + if (IS_ERR(ksm_thread)) { + pr_err("ksm: creating kthread failed\n"); + err = PTR_ERR(ksm_thread); + goto out_free; + } + +#ifdef CONFIG_SYSFS + err = sysfs_create_group(mm_kobj, &ksm_attr_group); + if (err) { + pr_err("ksm: register sysfs failed\n"); + kthread_stop(ksm_thread); + goto out_free; + } +#else + ksm_run = KSM_RUN_MERGE; /* no way for user to start it */ + +#endif /* CONFIG_SYSFS */ + +#ifdef CONFIG_MEMORY_HOTREMOVE + /* There is no significance to this priority 100 */ + hotplug_memory_notifier(ksm_memory_callback, 100); +#endif + return 0; + +out_free: + ksm_slab_free(); +out: + return err; +} +subsys_initcall(ksm_init); |