We need a stable value of memcg_max_cache_ids in kmem_cache_create() (memcg_alloc_cache_params() wants it for root caches), where we only hold the slab_mutex and no memcg-related locks. As a result, we have to update memcg_cache_ids under the slab_mutex, which we can only take from the slab's side. This looks awkward and will become even worse when per-memcg list_lru is introduced, which also wants stable access to memcg_max_cache_ids.
To get rid of this dependency between the memcg_max_cache_ids and the slab_mutex, this patch introduces a special rwsem. The rwsem is held for writing during memcg_caches arrays relocation and memcg_max_cache_ids updates. Therefore one can take it for reading to get a stable access to memcg_caches arrays and/or memcg_max_cache_ids. Currently the semaphore is taken for reading only from kmem_cache_create, right before taking the slab_mutex, so right now there's no point in using rwsem instead of mutex. However, once list_lru is made per-memcg it will allow list_lru initializations to proceed concurrently. Signed-off-by: Vladimir Davydov <[email protected]> --- include/linux/memcontrol.h | 15 +++++++++++++-- mm/memcontrol.c | 28 ++++++++++++++++++---------- mm/slab_common.c | 10 +++++----- 3 files changed, 36 insertions(+), 17 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 7c1bf0a84950..f2cd342d6544 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -419,8 +419,13 @@ extern struct static_key memcg_kmem_enabled_key; * The maximal number of kmem-active memory cgroups that can exist on the * system. May grow, but never shrinks. The value returned by memcg_cache_id() * is always less. + * + * To prevent memcg_max_cache_ids from growing, memcg_lock_cache_id_space() can + * be used. It's backed by rw semaphore. */ extern int memcg_max_cache_ids; +extern void memcg_lock_cache_id_space(void); +extern void memcg_unlock_cache_id_space(void); static inline bool memcg_kmem_enabled(void) { @@ -449,8 +454,6 @@ void __memcg_kmem_uncharge_pages(struct page *page, int order); int memcg_cache_id(struct mem_cgroup *memcg); -void memcg_update_array_size(int num_groups); - struct kmem_cache * __memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp); @@ -587,6 +590,14 @@ static inline int memcg_cache_id(struct mem_cgroup *memcg) return -1; } +static inline void memcg_lock_cache_id_space(void) +{ +} + +static inline void memcg_unlock_cache_id_space(void) +{ +} + static inline struct kmem_cache * memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp) { diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 0020824dee96..0c6d412ae5a3 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -621,6 +621,19 @@ static void disarm_sock_keys(struct mem_cgroup *memcg) static DEFINE_IDA(memcg_cache_ida); int memcg_max_cache_ids; +/* Protects memcg_max_cache_ids */ +static DECLARE_RWSEM(memcg_cache_id_space_sem); + +void memcg_lock_cache_id_space(void) +{ + down_read(&memcg_cache_id_space_sem); +} + +void memcg_unlock_cache_id_space(void) +{ + up_read(&memcg_cache_id_space_sem); +} + /* * MIN_SIZE is different than 1, because we would like to avoid going through * the alloc/free process all the time. In a small machine, 4 kmem-limited @@ -2937,6 +2950,7 @@ static int memcg_alloc_cache_id(void) * There's no space for the new id in memcg_caches arrays, * so we have to grow them. */ + down_write(&memcg_cache_id_space_sem); size = 2 * (id + 1); if (size < MEMCG_CACHES_MIN_SIZE) @@ -2948,6 +2962,10 @@ static int memcg_alloc_cache_id(void) err = memcg_update_all_caches(size); mutex_unlock(&memcg_slab_mutex); + if (!err) + memcg_max_cache_ids = size; + up_write(&memcg_cache_id_space_sem); + if (err) { ida_simple_remove(&memcg_cache_ida, id); return err; @@ -2961,16 +2979,6 @@ static void memcg_free_cache_id(int id) ida_simple_remove(&memcg_cache_ida, id); } -/* - * We should update the current array size iff all caches updates succeed. This - * can only be done from the slab side. The slab mutex needs to be held when - * calling this. - */ -void memcg_update_array_size(int num) -{ - memcg_max_cache_ids = num; -} - static void memcg_register_cache(struct mem_cgroup *memcg, struct kmem_cache *root_cache) { diff --git a/mm/slab_common.c b/mm/slab_common.c index cc6e18437f6c..4e2b9040a49f 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -157,8 +157,8 @@ int memcg_update_all_caches(int num_memcgs) { struct kmem_cache *s; int ret = 0; - mutex_lock(&slab_mutex); + mutex_lock(&slab_mutex); list_for_each_entry(s, &slab_caches, list) { if (!is_root_cache(s)) continue; @@ -169,11 +169,8 @@ int memcg_update_all_caches(int num_memcgs) * up to this point in an updated state. */ if (ret) - goto out; + break; } - - memcg_update_array_size(num_memcgs); -out: mutex_unlock(&slab_mutex); return ret; } @@ -290,6 +287,8 @@ kmem_cache_create(const char *name, size_t size, size_t align, get_online_cpus(); get_online_mems(); + memcg_lock_cache_id_space(); /* memcg_alloc_cache_params() needs a + stable value of memcg_max_cache_ids */ mutex_lock(&slab_mutex); @@ -328,6 +327,7 @@ kmem_cache_create(const char *name, size_t size, size_t align, out_unlock: mutex_unlock(&slab_mutex); + memcg_unlock_cache_id_space(); put_online_mems(); put_online_cpus(); -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
