| // 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/fs.h> |
| #include <linux/mman.h> |
| #include <linux/sched.h> |
| #include <linux/sched/mm.h> |
| #include <linux/sched/coredump.h> |
| #include <linux/rwsem.h> |
| #include <linux/pagemap.h> |
| #include <linux/rmap.h> |
| #include <linux/spinlock.h> |
| #include <linux/xxhash.h> |
| #include <linux/delay.h> |
| #include <linux/kthread.h> |
| #include <linux/wait.h> |
| #include <linux/slab.h> |
| #include <linux/rbtree.h> |
| #include <linux/memory.h> |
| #include <linux/mmu_notifier.h> |
| #include <linux/swap.h> |
| #include <linux/ksm.h> |
| #include <linux/hashtable.h> |
| #include <linux/freezer.h> |
| #include <linux/oom.h> |
| #include <linux/numa.h> |
| |
| #include <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 DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait); |
| static DEFINE_MUTEX(ksm_thread_mutex); |
| static DEFINE_SPINLOCK(ksm_mmlist_lock); |
| |
| #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("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 = 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 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); |
| } |
| |
| enum get_ksm_page_flags { |
| GET_KSM_PAGE_NOLOCK, |
| GET_KSM_PAGE_LOCK, |
| GET_KSM_PAGE_TRYLOCK |
| }; |
| |
| /* |
| * get_ksm_page: checks if the page indicated by the stable node |
| * is still its ksm page, despite having held no reference to it. |
| * In which case we can trust the content of the page, and it |
| * returns the gotten page; but if the page has now been zapped, |
| * remove the stale node from the stable tree and return NULL. |
| * But beware, the stable node's page might be being migrated. |
| * |
| * You would expect the stable_node to hold a reference to the ksm page. |
| * But if it increments the page's count, swapping out has to wait for |
| * ksmd to come around again before it can free the page, which may take |
| * seconds or even minutes: much too unresponsive. So instead we use a |
| * "keyhole reference": access to the ksm page from the stable node peeps |
| * out through its keyhole to see if that page still holds the right key, |
| * pointing back to this stable node. This relies on freeing a PageAnon |
| * page to reset its page->mapping to NULL, and relies on no other use of |
| * a page to put something that might look like our key in page->mapping. |
| * is on its way to being freed; but it is an anomaly to bear in mind. |
| */ |
| static struct page *get_ksm_page(struct stable_node *stable_node, |
| enum get_ksm_page_flags flags) |
| { |
| struct page *page; |
| void *expected_mapping; |
| unsigned long kpfn; |
| |
| expected_mapping = (void *)((unsigned long)stable_node | |
| PAGE_MAPPING_KSM); |
| again: |
| kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */ |
| page = pfn_to_page(kpfn); |
| if (READ_ONCE(page->mapping) != expected_mapping) |
| goto stale; |
| |
| /* |
| * We cannot do anything with the page while its refcount is 0. |
| * Usually 0 means free, or tail of a higher-order page: in which |
| * case this node is no longer referenced, and should be freed; |
| * however, it might mean that the page is under page_ref_freeze(). |
| * The __remove_mapping() case is easy, again the node is now stale; |
| * the same is in reuse_ksm_page() case; but if page is swapcache |
| * in 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 (flags == GET_KSM_PAGE_TRYLOCK) { |
| if (!trylock_page(page)) { |
| put_page(page); |
| return ERR_PTR(-EBUSY); |
| } |
| } else if (flags == GET_KSM_PAGE_LOCK) |
| lock_page(page); |
| |
| if (flags != GET_KSM_PAGE_NOLOCK) { |
| if (READ_ONCE(page->mapping) != expected_mapping) { |
| unlock_page(page); |
| put_page(page); |
| goto stale; |
| } |
| } |
| return page; |
| |
| stale: |
| /* |
| * We come here from above when page->mapping or !PageSwapCache |
| * suggests that the node is stale; but it might be under migration. |
| * We need smp_rmb(), matching the smp_wmb() in 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, GET_KSM_PAGE_LOCK); |
| if (!page) |
| goto out; |
| |
| hlist_del(&rmap_item->hlist); |
| unlock_page(page); |
| put_page(page); |
| |
| if (!hlist_empty(&stable_node->hlist)) |
| ksm_pages_sharing--; |
| else |
| ksm_pages_shared--; |
| 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; |
| |
| } 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, GET_KSM_PAGE_LOCK); |
| if (!page) { |
| /* |
| * get_ksm_page did remove_node_from_stable_tree itself. |
| */ |
| return 0; |
| } |
| |
| /* |
| * Page could be still mapped if this races with __mmput() running in |
| * between ksm_exit() and exit_mmap(). Just refuse to let |
| * merge_across_nodes/max_page_sharing be switched. |
| */ |
| err = -EBUSY; |
| if (!page_mapped(page)) { |
| /* |
| * The stable node did not yet appear stale to get_ksm_page(), |
| * since that allows for an unmapped ksm page to be recognized |
| * right up until it is freed; but the node is safe to remove. |
| * This page might be in 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 = xxhash(addr, PAGE_SIZE, 0); |
| kunmap_atomic(addr); |
| return checksum; |
| } |
| |
| static int write_protect_page(struct vm_area_struct *vma, struct page *page, |
| pte_t *orig_pte) |
| { |
| struct mm_struct *mm = vma->vm_mm; |
| struct page_vma_mapped_walk pvmw = { |
| .page = page, |
| .vma = vma, |
| }; |
| int swapped; |
| int err = -EFAULT; |
| struct mmu_notifier_range range; |
| |
| pvmw.address = page_address_in_vma(page, vma); |
| if (pvmw.address == -EFAULT) |
| goto out; |
| |
| BUG_ON(PageTransCompound(page)); |
| |
| mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, 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; |
| |
| 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(&range); |
| out: |
| return err; |
| } |
| |
| /** |
| * replace_page - replace page in vma by new ksm page |
| * @vma: vma that holds the pte pointing to page |
| * @page: the page we are replacing by kpage |
| * @kpage: the ksm page we replace page by |
| * @orig_pte: the original value of the pte |
| * |
| * Returns 0 on success, -EFAULT on failure. |
| */ |
| static int replace_page(struct vm_area_struct *vma, struct page *page, |
| struct page *kpage, pte_t orig_pte) |
| { |
| struct mm_struct *mm = vma->vm_mm; |
| pmd_t *pmd; |
| pte_t *ptep; |
| pte_t newpte; |
| spinlock_t *ptl; |
| unsigned long addr; |
| int err = -EFAULT; |
| struct mmu_notifier_range range; |
| |
| addr = page_address_in_vma(page, vma); |
| if (addr == -EFAULT) |
| goto out; |
| |
| pmd = mm_find_pmd(mm, addr); |
| if (!pmd) |
| goto out; |
| |
| mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr, |
| addr + PAGE_SIZE); |
| mmu_notifier_invalidate_range_start(&range); |
| |
| 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(&range); |
| out: |
| return err; |
| } |
| |
| /* |
| * try_to_merge_one_page - take two pages and merge them into one |
| * @vma: the vma that holds the pte pointing to page |
| * @page: the PageAnon page that we want to replace with kpage |
| * @kpage: the PageKsm page that we want to map instead of page, |
| * or NULL the first time when we want to use page as kpage. |
| * |
| * This function returns 0 if the pages were merged, -EFAULT otherwise. |
| */ |
| static int try_to_merge_one_page(struct vm_area_struct *vma, |
| struct page *page, struct page *kpage) |
| { |
| pte_t orig_pte = __pte(0); |
| int err = -EFAULT; |
| |
| if (page == kpage) /* ksm page forked */ |
| return 0; |
| |
| if (!PageAnon(page)) |
| goto out; |
| |
| /* |
| * We need the page lock to read a stable PageSwapCache in |
| * write_protect_page(). We use trylock_page() instead of |
| * lock_page() because we don't want to wait here - we |
| * prefer to continue scanning and merging different pages, |
| * then come back to this page when it is unlocked. |
| */ |
| if (!trylock_page(page)) |
| goto out; |
| |
| if (PageTransCompound(page)) { |
| if (split_huge_page(page)) |
| goto out_unlock; |
| } |
| |
| /* |
| * If this anonymous page is mapped only here, its pte may need |
| * to be write-protected. If it's mapped elsewhere, all of its |
| * ptes are necessarily already write-protected. But in either |
| * case, we need to lock and check page_count is not raised. |
| */ |
| if (write_protect_page(vma, page, &orig_pte) == 0) { |
| if (!kpage) { |
| /* |
| * While we hold page lock, upgrade page from |
| * PageAnon+anon_vma to PageKsm+NULL stable_node: |
| * stable_tree_insert() will update stable_node. |
| */ |
| set_page_stable_node(page, NULL); |
| mark_page_accessed(page); |
| /* |
| * Page reclaim just frees a clean page with no dirty |
| * ptes: make sure that the ksm page would be swapped. |
| */ |
| if (!PageDirty(page)) |
| SetPageDirty(page); |
| err = 0; |
| } else if (pages_identical(page, kpage)) |
| err = replace_page(vma, page, kpage, orig_pte); |
| } |
| |
| 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, GET_KSM_PAGE_NOLOCK); |
| if (!_tree_page) |
| continue; |
| nr += 1; |
| if (is_page_sharing_candidate(dup)) { |
| if (!found || |
| dup->rmap_hlist_len > found_rmap_hlist_len) { |
| if (found) |
| put_page(tree_page); |
| found = dup; |
| found_rmap_hlist_len = found->rmap_hlist_len; |
| tree_page = _tree_page; |
| |
| /* skip put_page for found dup */ |
| if (!prune_stale_stable_nodes) |
| break; |
| continue; |
| } |
| } |
| put_page(_tree_page); |
| } |
| |
| if (found) { |
| /* |
| * nr is counting all dups in the chain only if |
| * prune_stale_stable_nodes is true, otherwise we may |
| * break the loop at nr == 1 even if there are |
| * multiple entries. |
| */ |
| if (prune_stale_stable_nodes && nr == 1) { |
| /* |
| * If there's not just one entry it would |
| * corrupt memory, better BUG_ON. In KSM |
| * context with no lock held it's not even |
| * fatal. |
| */ |
| BUG_ON(stable_node->hlist.first->next); |
| |
| /* |
| * There's just one entry and it is below the |
| * deduplication limit so drop the chain. |
| */ |
| rb_replace_node(&stable_node->node, &found->node, |
| root); |
| free_stable_node(stable_node); |
| ksm_stable_node_chains--; |
| ksm_stable_node_dups--; |
| /* |
| * NOTE: the caller depends on the stable_node |
| * to be equal to stable_node_dup if the chain |
| * was collapsed. |
| */ |
| *_stable_node = found; |
| /* |
| * Just for 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, GET_KSM_PAGE_NOLOCK); |
| } |
| /* |
| * _stable_node_dup set to NULL means the stable_node |
| * reached the ksm_max_page_sharing limit. |
| */ |
| *_stable_node_dup = NULL; |
| return NULL; |
| } |
| return stable_node_dup(_stable_node_dup, _stable_node, root, |
| prune_stale_stable_nodes); |
| } |
| |
| static __always_inline struct page *chain_prune(struct 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, |
| GET_KSM_PAGE_NOLOCK); |
| } |
| VM_BUG_ON(!stable_node_dup ^ !!stable_node_any); |
| if (!tree_page) { |
| /* |
| * If we walked over a stale stable_node, |
| * get_ksm_page() will call rb_erase() and it |
| * may rebalance the tree from under us. So |
| * restart the search from scratch. Returning |
| * NULL would be safe too, but we'd generate |
| * false negative insertions just because some |
| * stable_node was stale. |
| */ |
| goto again; |
| } |
| |
| ret = memcmp_pages(page, tree_page); |
| put_page(tree_page); |
| |
| parent = *new; |
| if (ret < 0) |
| new = &parent->rb_left; |
| else if (ret > 0) |
| new = &parent->rb_right; |
| else { |
| if (page_node) { |
| VM_BUG_ON(page_node->head != &migrate_nodes); |
| /* |
| * Test if the migrated page should be merged |
| * into a stable node dup. If the mapcount is |
| * 1 we can migrate it with another KSM page |
| * without adding it to the chain. |
| */ |
| if (page_mapcount(page) > 1) |
| goto chain_append; |
| } |
| |
| if (!stable_node_dup) { |
| /* |
| * If the stable_node is a chain and |
| * we got a payload match in memcmp |
| * but we cannot merge the scanned |
| * page in any of the existing |
| * stable_node dups because they're |
| * all full, we need to wait the |
| * scanned page to find itself a match |
| * in the unstable tree to create a |
| * brand new KSM page to add later to |
| * the dups of this stable_node. |
| */ |
| return NULL; |
| } |
| |
| /* |
| * Lock and unlock the stable_node's page (which |
| * might already have been migrated) so that page |
| * migration is sure to notice its raised count. |
| * It would be more elegant to return stable_node |
| * than kpage, but that involves more changes. |
| */ |
| tree_page = get_ksm_page(stable_node_dup, |
| GET_KSM_PAGE_TRYLOCK); |
| |
| if (PTR_ERR(tree_page) == -EBUSY) |
| return ERR_PTR(-EBUSY); |
| |
| if (unlikely(!tree_page)) |
| /* |
| * The tree may have been rebalanced, |
| * so re-evaluate parent and new. |
| */ |
| goto again; |
| unlock_page(tree_page); |
| |
| if (get_kpfn_nid(stable_node_dup->kpfn) != |
| NUMA(stable_node_dup->nid)) { |
| put_page(tree_page); |
| goto replace; |
| } |
| return tree_page; |
| } |
| } |
| |
| if (!page_node) |
| return NULL; |
| |
| list_del(&page_node->list); |
| DO_NUMA(page_node->nid = nid); |
| rb_link_node(&page_node->node, parent, new); |
| rb_insert_color(&page_node->node, root); |
| out: |
| if (is_page_sharing_candidate(page_node)) { |
| get_page(page); |
| return page; |
| } else |
| return NULL; |
| |
| replace: |
| /* |
| * If stable_node was a chain and chain_prune collapsed it, |
| * stable_node has been updated to be the new regular |
| * stable_node. A collapse of the chain is indistinguishable |
| * from the case there was no chain in the stable |
| * rbtree. Otherwise stable_node is the chain and |
| * stable_node_dup is the dup to replace. |
| */ |
| if (stable_node_dup == stable_node) { |
| VM_BUG_ON(is_stable_node_chain(stable_node_dup)); |
| VM_BUG_ON(is_stable_node_dup(stable_node_dup)); |
| /* there is no chain */ |
| if (page_node) { |
| VM_BUG_ON(page_node->head != &migrate_nodes); |
| list_del(&page_node->list); |
| DO_NUMA(page_node->nid = nid); |
| rb_replace_node(&stable_node_dup->node, |
| &page_node->node, |
| root); |
| if (is_page_sharing_candidate(page_node)) |
| get_page(page); |
| else |
| page = NULL; |
| } else { |
| rb_erase(&stable_node_dup->node, root); |
| page = NULL; |
| } |
| } else { |
| VM_BUG_ON(!is_stable_node_chain(stable_node)); |
| __stable_node_dup_del(stable_node_dup); |
| if (page_node) { |
| VM_BUG_ON(page_node->head != &migrate_nodes); |
| list_del(&page_node->list); |
| DO_NUMA(page_node->nid = nid); |
| stable_node_chain_add_dup(page_node, stable_node); |
| if (is_page_sharing_candidate(page_node)) |
| get_page(page); |
| else |
| page = NULL; |
| } else { |
| page = NULL; |
| } |
| } |
| stable_node_dup->head = &migrate_nodes; |
| list_add(&stable_node_dup->list, stable_node_dup->head); |
| return page; |
| |
| chain_append: |
| /* stable_node_dup could be null if it reached the limit */ |
| if (!stable_node_dup) |
| stable_node_dup = stable_node_any; |
| /* |
| * If stable_node was a chain and chain_prune collapsed it, |
| * stable_node has been updated to be the new regular |
| * stable_node. A collapse of the chain is indistinguishable |
| * from the case there was no chain in the stable |
| * rbtree. Otherwise stable_node is the chain and |
| * stable_node_dup is the dup to replace. |
| */ |
| if (stable_node_dup == stable_node) { |
| VM_BUG_ON(is_stable_node_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, |
| GET_KSM_PAGE_NOLOCK); |
| } |
| VM_BUG_ON(!stable_node_dup ^ !!stable_node_any); |
| if (!tree_page) { |
| /* |
| * If we walked over a stale stable_node, |
| * get_ksm_page() will call rb_erase() and it |
| * may rebalance the tree from under us. So |
| * restart the search from scratch. Returning |
| * NULL would be safe too, but we'd generate |
| * false negative insertions just because some |
| * stable_node was stale. |
| */ |
| goto again; |
| } |
| |
| ret = memcmp_pages(kpage, tree_page); |
| put_page(tree_page); |
| |
| parent = *new; |
| if (ret < 0) |
| new = &parent->rb_left; |
| else if (ret > 0) |
| new = &parent->rb_right; |
| else { |
| need_chain = true; |
| break; |
| } |
| } |
| |
| stable_node_dup = alloc_stable_node(); |
| if (!stable_node_dup) |
| return NULL; |
| |
| INIT_HLIST_HEAD(&stable_node_dup->hlist); |
| stable_node_dup->kpfn = kpfn; |
| set_page_stable_node(kpage, stable_node_dup); |
| stable_node_dup->rmap_hlist_len = 0; |
| DO_NUMA(stable_node_dup->nid = nid); |
| if (!need_chain) { |
| rb_link_node(&stable_node_dup->node, parent, new); |
| rb_insert_color(&stable_node_dup->node, root); |
| } else { |
| if (!is_stable_node_chain(stable_node)) { |
| struct 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) { |
| if (PTR_ERR(kpage) == -EBUSY) |
| return; |
| |
| err = try_to_merge_with_ksm_page(rmap_item, page, kpage); |
| if (!err) { |
| /* |
| * The page was successfully merged: |
| * add its rmap_item to the stable tree. |
| */ |
| lock_page(kpage); |
| stable_tree_append(rmap_item, page_stable_node(kpage), |
| max_page_sharing_bypass); |
| unlock_page(kpage); |
| } |
| put_page(kpage); |
| return; |
| } |
| |
| /* |
| * If the hash value of the page has changed from the last time |
| * we calculated it, this page is changing frequently: therefore we |
| * don't want to insert it in the unstable tree, and we don't want |
| * to waste our time searching for something identical to it there. |
| */ |
| checksum = calc_checksum(page); |
| if (rmap_item->oldchecksum != checksum) { |
| rmap_item->oldchecksum = checksum; |
| return; |
| } |
| |
| /* |
| * Same checksum as an empty page. We attempt to merge it with the |
| * appropriate zero page if the user enabled this via sysfs. |
| */ |
| if (ksm_use_zero_pages && (checksum == zero_checksum)) { |
| struct vm_area_struct *vma; |
| |
| down_read(&mm->mmap_sem); |
| vma = find_mergeable_vma(mm, rmap_item->address); |
| err = try_to_merge_one_page(vma, page, |
| ZERO_PAGE(rmap_item->address)); |
| 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, |
| GET_KSM_PAGE_NOLOCK); |
| if (page) |
| put_page(page); |
| cond_resched(); |
| } |
| } |
| |
| for (nid = 0; nid < ksm_nr_node_ids; nid++) |
| root_unstable_tree[nid] = RB_ROOT; |
| |
| spin_lock(&ksm_mmlist_lock); |
| slot = list_entry(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) |
| { |
| unsigned int sleep_ms; |
| |
| set_freezable(); |
| set_user_nice(current, 5); |
| |
| while (!kthread_should_stop()) { |
| mutex_lock(&ksm_thread_mutex); |
| wait_while_offlining(); |
| if (ksmd_should_run()) |
| ksm_do_scan(ksm_thread_pages_to_scan); |
| mutex_unlock(&ksm_thread_mutex); |
| |
| try_to_freeze(); |
| |
| if (ksmd_should_run()) { |
| sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs); |
| wait_event_interruptible_timeout(ksm_iter_wait, |
| sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs), |
| msecs_to_jiffies(sleep_ms)); |
| } else { |
| wait_event_freezable(ksm_thread_wait, |
| ksmd_should_run() || kthread_should_stop()); |
| } |
| } |
| return 0; |
| } |
| |
| 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; |
| } |
| EXPORT_SYMBOL_GPL(ksm_madvise); |
| |
| 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; |
| } |
| |
| bool reuse_ksm_page(struct page *page, |
| struct vm_area_struct *vma, |
| unsigned long address) |
| { |
| #ifdef CONFIG_DEBUG_VM |
| if (WARN_ON(is_zero_pfn(page_to_pfn(page))) || |
| WARN_ON(!page_mapped(page)) || |
| WARN_ON(!PageLocked(page))) { |
| dump_page(page, "reuse_ksm_page"); |
| return false; |
| } |
| #endif |
| |
| if (PageSwapCache(page) || !page_stable_node(page)) |
| return false; |
| /* Prohibit parallel get_ksm_page() */ |
| if (!page_ref_freeze(page, 1)) |
| return false; |
| |
| page_move_anon_rmap(page, vma); |
| page->index = linear_page_index(vma, address); |
| page_ref_unfreeze(page, 1); |
| |
| return true; |
| } |
| #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; |
| 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 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); |