diff options
Diffstat (limited to 'mm/ksm.c')
| -rw-r--r-- | mm/ksm.c | 820 |
1 files changed, 754 insertions, 66 deletions
@@ -128,9 +128,12 @@ struct ksm_scan { * 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 { @@ -138,11 +141,24 @@ struct stable_node { struct rb_node node; /* when node of stable tree */ struct { /* when listed for migration */ struct list_head *head; - struct list_head list; + struct { + struct hlist_node hlist_dup; + struct list_head list; + }; }; }; struct hlist_head hlist; - unsigned long kpfn; + 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 @@ -192,6 +208,7 @@ 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); @@ -219,6 +236,18 @@ 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; @@ -287,6 +316,45 @@ static void __init ksm_slab_free(void) 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; @@ -317,6 +385,8 @@ static inline struct stable_node *alloc_stable_node(void) 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); } @@ -498,25 +568,82 @@ static inline int get_kpfn_nid(unsigned long kpfn) return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn)); } +static struct stable_node *alloc_stable_node_chain(struct stable_node *dup, + struct rb_root *root) +{ + struct stable_node *chain = alloc_stable_node(); + VM_BUG_ON(is_stable_node_chain(dup)); + if (likely(chain)) { + INIT_HLIST_HEAD(&chain->hlist); + chain->chain_prune_time = jiffies; + chain->rmap_hlist_len = STABLE_NODE_CHAIN; +#if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA) + chain->nid = -1; /* debug */ +#endif + ksm_stable_node_chains++; + + /* + * Put the stable node chain in the first dimension of + * the stable tree and at the same time remove the old + * stable node. + */ + rb_replace_node(&dup->node, &chain->node, root); + + /* + * Move the old stable node to the second dimension + * queued in the hlist_dup. The invariant is that all + * dup stable_nodes in the chain->hlist point to pages + * that are wrprotected and have the exact same + * content. + */ + stable_node_chain_add_dup(dup, chain); + } + return chain; +} + +static inline void free_stable_node_chain(struct stable_node *chain, + struct rb_root *root) +{ + rb_erase(&chain->node, root); + free_stable_node(chain); + ksm_stable_node_chains--; +} + static void remove_node_from_stable_tree(struct stable_node *stable_node) { struct rmap_item *rmap_item; + /* check it's not STABLE_NODE_CHAIN or negative */ + BUG_ON(stable_node->rmap_hlist_len < 0); + hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) { if (rmap_item->hlist.next) ksm_pages_sharing--; else ksm_pages_shared--; + VM_BUG_ON(stable_node->rmap_hlist_len <= 0); + stable_node->rmap_hlist_len--; put_anon_vma(rmap_item->anon_vma); rmap_item->address &= PAGE_MASK; cond_resched(); } + /* + * We need the second aligned pointer of the migrate_nodes + * list_head to stay clear from the rb_parent_color union + * (aligned and different than any node) and also different + * from &migrate_nodes. This will verify that future list.h changes + * don't break STABLE_NODE_DUP_HEAD. + */ +#if GCC_VERSION >= 40903 /* only recent gcc can handle it */ + BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes); + BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1); +#endif + if (stable_node->head == &migrate_nodes) list_del(&stable_node->list); else - rb_erase(&stable_node->node, - root_stable_tree + NUMA(stable_node->nid)); + stable_node_dup_del(stable_node); free_stable_node(stable_node); } @@ -635,6 +762,8 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) 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; @@ -743,6 +872,31 @@ static int remove_stable_node(struct stable_node *stable_node) 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; @@ -753,7 +907,8 @@ static int remove_all_stable_nodes(void) 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(stable_node)) { + if (remove_stable_node_chain(stable_node, + root_stable_tree + nid)) { err = -EBUSY; break; /* proceed to next nid */ } @@ -1138,6 +1293,214 @@ static struct page *try_to_merge_two_pages(struct rmap_item *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); +} + +struct page *stable_node_dup(struct stable_node **_stable_node_dup, + struct stable_node **_stable_node, + struct rb_root *root, + bool prune_stale_stable_nodes) +{ + struct stable_node *dup, *found = NULL, *stable_node = *_stable_node; + struct hlist_node *hlist_safe; + struct page *_tree_page, *tree_page = NULL; + int nr = 0; + int found_rmap_hlist_len; + + if (!prune_stale_stable_nodes || + time_before(jiffies, stable_node->chain_prune_time + + msecs_to_jiffies( + ksm_stable_node_chains_prune_millisecs))) + prune_stale_stable_nodes = false; + else + stable_node->chain_prune_time = jiffies; + + hlist_for_each_entry_safe(dup, hlist_safe, + &stable_node->hlist, hlist_dup) { + cond_resched(); + /* + * We must walk all stable_node_dup to prune the stale + * stable nodes during lookup. + * + * get_ksm_page can drop the nodes from the + * stable_node->hlist if they point to freed pages + * (that's why we do a _safe walk). The "dup" + * stable_node parameter itself will be freed from + * under us if it returns NULL. + */ + _tree_page = get_ksm_page(dup, false); + if (!_tree_page) + continue; + nr += 1; + if (is_page_sharing_candidate(dup)) { + if (!found || + dup->rmap_hlist_len > found_rmap_hlist_len) { + if (found) + put_page(tree_page); + found = dup; + found_rmap_hlist_len = found->rmap_hlist_len; + tree_page = _tree_page; + + /* skip put_page for found dup */ + if (!prune_stale_stable_nodes) + break; + continue; + } + } + put_page(_tree_page); + } + + if (found) { + /* + * nr is counting all dups in the chain only if + * prune_stale_stable_nodes is true, otherwise we may + * break the loop at nr == 1 even if there are + * multiple entries. + */ + if (prune_stale_stable_nodes && nr == 1) { + /* + * If there's not just one entry it would + * corrupt memory, better BUG_ON. In KSM + * context with no lock held it's not even + * fatal. + */ + BUG_ON(stable_node->hlist.first->next); + + /* + * There's just one entry and it is below the + * deduplication limit so drop the chain. + */ + rb_replace_node(&stable_node->node, &found->node, + root); + free_stable_node(stable_node); + ksm_stable_node_chains--; + ksm_stable_node_dups--; + /* + * NOTE: the caller depends on the stable_node + * to be equal to stable_node_dup if the chain + * was collapsed. + */ + *_stable_node = found; + /* + * Just for robustneess as stable_node is + * otherwise left as a stable pointer, the + * compiler shall optimize it away at build + * time. + */ + stable_node = NULL; + } else if (stable_node->hlist.first != &found->hlist_dup && + __is_page_sharing_candidate(found, 1)) { + /* + * If the found stable_node dup can accept one + * more future merge (in addition to the one + * that is underway) and is not at the head of + * the chain, put it there so next search will + * be quicker in the !prune_stale_stable_nodes + * case. + * + * NOTE: it would be inaccurate to use nr > 1 + * instead of checking the hlist.first pointer + * directly, because in the + * prune_stale_stable_nodes case "nr" isn't + * the position of the found dup in the chain, + * but the total number of dups in the chain. + */ + hlist_del(&found->hlist_dup); + hlist_add_head(&found->hlist_dup, + &stable_node->hlist); + } + } + + *_stable_node_dup = found; + return tree_page; +} + +static struct stable_node *stable_node_dup_any(struct stable_node *stable_node, + struct rb_root *root) +{ + if (!is_stable_node_chain(stable_node)) + return stable_node; + if (hlist_empty(&stable_node->hlist)) { + free_stable_node_chain(stable_node, root); + return NULL; + } + return hlist_entry(stable_node->hlist.first, + typeof(*stable_node), hlist_dup); +} + +/* + * Like for get_ksm_page, this function can free the *_stable_node and + * *_stable_node_dup if the returned tree_page is NULL. + * + * It can also free and overwrite *_stable_node with the found + * stable_node_dup if the chain is collapsed (in which case + * *_stable_node will be equal to *_stable_node_dup like if the chain + * never existed). It's up to the caller to verify tree_page is not + * NULL before dereferencing *_stable_node or *_stable_node_dup. + * + * *_stable_node_dup is really a second output parameter of this + * function and will be overwritten in all cases, the caller doesn't + * need to initialize it. + */ +static struct page *__stable_node_chain(struct stable_node **_stable_node_dup, + struct stable_node **_stable_node, + struct rb_root *root, + bool prune_stale_stable_nodes) +{ + struct stable_node *stable_node = *_stable_node; + if (!is_stable_node_chain(stable_node)) { + if (is_page_sharing_candidate(stable_node)) { + *_stable_node_dup = stable_node; + return get_ksm_page(stable_node, false); + } + /* + * _stable_node_dup set to NULL means the stable_node + * reached the ksm_max_page_sharing limit. + */ + *_stable_node_dup = NULL; + return NULL; + } + return stable_node_dup(_stable_node_dup, _stable_node, root, + prune_stale_stable_nodes); +} + +static __always_inline struct page *chain_prune(struct stable_node **s_n_d, + struct stable_node **s_n, + struct rb_root *root) +{ + return __stable_node_chain(s_n_d, s_n, root, true); +} + +static __always_inline struct page *chain(struct stable_node **s_n_d, + struct stable_node *s_n, + struct rb_root *root) +{ + struct stable_node *old_stable_node = s_n; + struct page *tree_page; + + tree_page = __stable_node_chain(s_n_d, &s_n, root, false); + /* not pruning dups so s_n cannot have changed */ + VM_BUG_ON(s_n != old_stable_node); + return tree_page; +} + /* * stable_tree_search - search for page inside the stable tree * @@ -1153,7 +1516,7 @@ static struct page *stable_tree_search(struct page *page) struct rb_root *root; struct rb_node **new; struct rb_node *parent; - struct stable_node *stable_node; + struct stable_node *stable_node, *stable_node_dup, *stable_node_any; struct stable_node *page_node; page_node = page_stable_node(page); @@ -1175,7 +1538,44 @@ again: cond_resched(); stable_node = rb_entry(*new, struct stable_node, node); - tree_page = get_ksm_page(stable_node, false); + stable_node_any = NULL; + tree_page = chain_prune(&stable_node_dup, &stable_node, root); + /* + * NOTE: stable_node may have been freed by + * chain_prune() if the returned stable_node_dup is + * not NULL. stable_node_dup may have been inserted in + * the rbtree instead as a regular stable_node (in + * order to collapse the stable_node chain if a single + * stable_node dup was found in it). In such case the + * stable_node is overwritten by the calleee to point + * to the stable_node_dup that was collapsed in the + * stable rbtree and stable_node will be equal to + * stable_node_dup like if the chain never existed. + */ + if (!stable_node_dup) { + /* + * Either all stable_node dups were full in + * this stable_node chain, or this chain was + * empty and should be rb_erased. + */ + stable_node_any = stable_node_dup_any(stable_node, + root); + if (!stable_node_any) { + /* rb_erase just run */ + goto again; + } + /* + * Take any of the stable_node dups page of + * this stable_node chain to let the tree walk + * continue. All KSM pages belonging to the + * stable_node dups in a stable_node chain + * have the same content and they're + * wrprotected at all times. Any will work + * fine to continue the walk. + */ + tree_page = get_ksm_page(stable_node_any, false); + } + VM_BUG_ON(!stable_node_dup ^ !!stable_node_any); if (!tree_page) { /* * If we walked over a stale stable_node, @@ -1198,6 +1598,34 @@ again: 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 @@ -1205,23 +1633,21 @@ again: * It would be more elegant to return stable_node * than kpage, but that involves more changes. */ - tree_page = get_ksm_page(stable_node, true); - if (tree_page) { - unlock_page(tree_page); - if (get_kpfn_nid(stable_node->kpfn) != - NUMA(stable_node->nid)) { - put_page(tree_page); - goto replace; - } - return tree_page; - } - /* - * There is now a place for page_node, but the tree may - * have been rebalanced, so re-evaluate parent and new. - */ - if (page_node) + tree_page = get_ksm_page(stable_node_dup, true); + if (unlikely(!tree_page)) + /* + * The tree may have been rebalanced, + * so re-evaluate parent and new. + */ goto again; - return NULL; + 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; } } @@ -1232,22 +1658,95 @@ again: DO_NUMA(page_node->nid = nid); rb_link_node(&page_node->node, parent, new); rb_insert_color(&page_node->node, root); - get_page(page); - return page; +out: + if (is_page_sharing_candidate(page_node)) { + get_page(page); + return page; + } else + return NULL; replace: - if (page_node) { - list_del(&page_node->list); - DO_NUMA(page_node->nid = nid); - rb_replace_node(&stable_node->node, &page_node->node, root); - get_page(page); + /* + * 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 { - rb_erase(&stable_node->node, root); - page = NULL; + 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->head = &migrate_nodes; - list_add(&stable_node->list, stable_node->head); + 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; } /* @@ -1264,7 +1763,8 @@ static struct stable_node *stable_tree_insert(struct page *kpage) struct rb_root *root; struct rb_node **new; struct rb_node *parent; - struct stable_node *stable_node; + 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); @@ -1279,7 +1779,32 @@ again: cond_resched(); stable_node = rb_entry(*new, struct stable_node, node); - tree_page = get_ksm_page(stable_node, false); + stable_node_any = NULL; + tree_page = chain(&stable_node_dup, stable_node, root); + if (!stable_node_dup) { + /* + * Either all stable_node dups were full in + * this stable_node chain, or this chain was + * empty and should be rb_erased. + */ + stable_node_any = stable_node_dup_any(stable_node, + root); + if (!stable_node_any) { + /* rb_erase just run */ + goto again; + } + /* + * Take any of the stable_node dups page of + * this stable_node chain to let the tree walk + * continue. All KSM pages belonging to the + * stable_node dups in a stable_node chain + * have the same content and they're + * wrprotected at all times. Any will work + * fine to continue the walk. + */ + tree_page = get_ksm_page(stable_node_any, false); + } + VM_BUG_ON(!stable_node_dup ^ !!stable_node_any); if (!tree_page) { /* * If we walked over a stale stable_node, @@ -1302,27 +1827,37 @@ again: else if (ret > 0) new = &parent->rb_right; else { - /* - * It is not a bug that stable_tree_search() didn't - * find this node: because at that time our page was - * not yet write-protected, so may have changed since. - */ - return NULL; + need_chain = true; + break; } } - stable_node = alloc_stable_node(); - if (!stable_node) + stable_node_dup = alloc_stable_node(); + if (!stable_node_dup) return NULL; - INIT_HLIST_HEAD(&stable_node->hlist); - stable_node->kpfn = kpfn; - set_page_stable_node(kpage, stable_node); - DO_NUMA(stable_node->nid = nid); - rb_link_node(&stable_node->node, parent, new); - rb_insert_color(&stable_node->node, root); + 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; + return stable_node_dup; } /* @@ -1412,8 +1947,27 @@ struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item, * the same ksm page. */ static void stable_tree_append(struct rmap_item *rmap_item, - struct stable_node *stable_node) + 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); @@ -1441,19 +1995,26 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) 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(stable_node->kpfn) != NUMA(stable_node->nid)) { - rb_erase(&stable_node->node, - root_stable_tree + NUMA(stable_node->nid)); + 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 */ @@ -1473,7 +2034,8 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) * add its rmap_item to the stable tree. */ lock_page(kpage); - stable_tree_append(rmap_item, page_stable_node(kpage)); + stable_tree_append(rmap_item, page_stable_node(kpage), + max_page_sharing_bypass); unlock_page(kpage); } put_page(kpage); @@ -1523,8 +2085,10 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) lock_page(kpage); stable_node = stable_tree_insert(kpage); if (stable_node) { - stable_tree_append(tree_rmap_item, stable_node); - stable_tree_append(rmap_item, stable_node); + stable_tree_append(tree_rmap_item, stable_node, + false); + stable_tree_append(rmap_item, stable_node, + false); } unlock_page(kpage); @@ -2028,6 +2592,48 @@ static void wait_while_offlining(void) } } +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) { @@ -2039,15 +2645,12 @@ static void ksm_check_stable_tree(unsigned long start_pfn, node = rb_first(root_stable_tree + nid); while (node) { stable_node = rb_entry(node, struct stable_node, node); - 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); + if (stable_node_chain_remove_range(stable_node, + start_pfn, end_pfn, + root_stable_tree + + nid)) node = rb_first(root_stable_tree + nid); - } else + else node = rb_next(node); cond_resched(); } @@ -2293,6 +2896,47 @@ static ssize_t use_zero_pages_store(struct kobject *kobj, } 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) { @@ -2331,6 +2975,46 @@ static ssize_t pages_volatile_show(struct kobject *kobj, } 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) { @@ -2350,6 +3034,10 @@ static struct attribute *ksm_attrs[] = { #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, }; |