diff options
| -rw-r--r-- | include/linux/rmap.h | 15 | ||||
| -rw-r--r-- | mm/ksm.c | 17 | ||||
| -rw-r--r-- | mm/migrate.c | 10 | ||||
| -rw-r--r-- | mm/rmap.c | 46 |
4 files changed, 69 insertions, 19 deletions
diff --git a/include/linux/rmap.h b/include/linux/rmap.h index af43cb9a0506..dc9b3c0bf5d4 100644 --- a/include/linux/rmap.h +++ b/include/linux/rmap.h @@ -81,6 +81,13 @@ static inline int anonvma_external_refcount(struct anon_vma *anon_vma) { return atomic_read(&anon_vma->external_refcount); } + +static inline void get_anon_vma(struct anon_vma *anon_vma) +{ + atomic_inc(&anon_vma->external_refcount); +} + +void drop_anon_vma(struct anon_vma *); #else static inline void anonvma_external_refcount_init(struct anon_vma *anon_vma) { @@ -90,6 +97,14 @@ static inline int anonvma_external_refcount(struct anon_vma *anon_vma) { return 0; } + +static inline void get_anon_vma(struct anon_vma *anon_vma) +{ +} + +static inline void drop_anon_vma(struct anon_vma *anon_vma) +{ +} #endif /* CONFIG_KSM */ static inline struct anon_vma *page_anon_vma(struct page *page) @@ -318,19 +318,14 @@ static void hold_anon_vma(struct rmap_item *rmap_item, struct anon_vma *anon_vma) { rmap_item->anon_vma = anon_vma; - atomic_inc(&anon_vma->external_refcount); + get_anon_vma(anon_vma); } -static void drop_anon_vma(struct rmap_item *rmap_item) +static void ksm_drop_anon_vma(struct rmap_item *rmap_item) { struct anon_vma *anon_vma = rmap_item->anon_vma; - if (atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->root->lock)) { - int empty = list_empty(&anon_vma->head); - anon_vma_unlock(anon_vma); - if (empty) - anon_vma_free(anon_vma); - } + drop_anon_vma(anon_vma); } /* @@ -415,7 +410,7 @@ static void break_cow(struct rmap_item *rmap_item) * 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. */ - drop_anon_vma(rmap_item); + ksm_drop_anon_vma(rmap_item); down_read(&mm->mmap_sem); if (ksm_test_exit(mm)) @@ -470,7 +465,7 @@ static void remove_node_from_stable_tree(struct stable_node *stable_node) ksm_pages_sharing--; else ksm_pages_shared--; - drop_anon_vma(rmap_item); + ksm_drop_anon_vma(rmap_item); rmap_item->address &= PAGE_MASK; cond_resched(); } @@ -558,7 +553,7 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) else ksm_pages_shared--; - drop_anon_vma(rmap_item); + ksm_drop_anon_vma(rmap_item); rmap_item->address &= PAGE_MASK; } else if (rmap_item->address & UNSTABLE_FLAG) { diff --git a/mm/migrate.c b/mm/migrate.c index 5208fa1d9712..38e7cad782f4 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -639,7 +639,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private, * exist when the page is remapped later */ anon_vma = page_anon_vma(page); - atomic_inc(&anon_vma->external_refcount); + get_anon_vma(anon_vma); } } @@ -682,12 +682,8 @@ skip_unmap: rcu_unlock: /* Drop an anon_vma reference if we took one */ - if (anon_vma && atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->root->lock)) { - int empty = list_empty(&anon_vma->head); - anon_vma_unlock(anon_vma); - if (empty) - anon_vma_free(anon_vma); - } + if (anon_vma) + drop_anon_vma(anon_vma); if (rcu_locked) rcu_read_unlock(); diff --git a/mm/rmap.c b/mm/rmap.c index caa48b27371b..07e9814c7a41 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -235,6 +235,12 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma) * lock any of the anon_vmas in this anon_vma tree. */ anon_vma->root = pvma->anon_vma->root; + /* + * With KSM refcounts, an anon_vma can stay around longer than the + * process it belongs to. The root anon_vma needs to be pinned + * until this anon_vma is freed, because the lock lives in the root. + */ + get_anon_vma(anon_vma->root); /* Mark this anon_vma as the one where our new (COWed) pages go. */ vma->anon_vma = anon_vma; anon_vma_chain_link(vma, avc, anon_vma); @@ -264,8 +270,12 @@ static void anon_vma_unlink(struct anon_vma_chain *anon_vma_chain) empty = list_empty(&anon_vma->head) && !anonvma_external_refcount(anon_vma); anon_vma_unlock(anon_vma); - if (empty) + if (empty) { + /* We no longer need the root anon_vma */ + if (anon_vma->root != anon_vma) + drop_anon_vma(anon_vma->root); anon_vma_free(anon_vma); + } } void unlink_anon_vmas(struct vm_area_struct *vma) @@ -1382,6 +1392,40 @@ int try_to_munlock(struct page *page) return try_to_unmap_file(page, TTU_MUNLOCK); } +#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION) +/* + * Drop an anon_vma refcount, freeing the anon_vma and anon_vma->root + * if necessary. Be careful to do all the tests under the lock. Once + * we know we are the last user, nobody else can get a reference and we + * can do the freeing without the lock. + */ +void drop_anon_vma(struct anon_vma *anon_vma) +{ + if (atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->root->lock)) { + struct anon_vma *root = anon_vma->root; + int empty = list_empty(&anon_vma->head); + int last_root_user = 0; + int root_empty = 0; + + /* + * The refcount on a non-root anon_vma got dropped. Drop + * the refcount on the root and check if we need to free it. + */ + if (empty && anon_vma != root) { + last_root_user = atomic_dec_and_test(&root->external_refcount); + root_empty = list_empty(&root->head); + } + anon_vma_unlock(anon_vma); + + if (empty) { + anon_vma_free(anon_vma); + if (root_empty && last_root_user) + anon_vma_free(root); + } + } +} +#endif + #ifdef CONFIG_MIGRATION /* * rmap_walk() and its helpers rmap_walk_anon() and rmap_walk_file(): |