We need a stable value of memcg_nr_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_nr_cache_ids under the slab_mutex, which we can only take on the slab's side (see memcg_update_array_size). This looks awkward and will become even worse when per-memcg list_lru is introduced, which also wants stable access to memcg_nr_cache_ids.
To get rid of this dependency between the memcg_nr_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_nr_cache_ids updates. Therefore one can take it for reading to get a stable access to memcg_caches arrays and/or memcg_nr_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 much 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 | 12 ++++++++++-- mm/memcontrol.c | 29 +++++++++++++++++++---------- mm/slab_common.c | 9 ++++----- 3 files changed, 33 insertions(+), 17 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index b27f183e65cd..8dafad6bb248 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -361,6 +361,8 @@ static inline void sock_release_memcg(struct sock *sk) extern struct static_key memcg_kmem_enabled_key; extern int memcg_nr_cache_ids; +extern void memcg_get_cache_ids(void); +extern void memcg_put_cache_ids(void); /* * Helper macro to loop through all memcg-specific caches. Callers must still @@ -396,8 +398,6 @@ 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); void __memcg_kmem_put_cache(struct kmem_cache *cachep); @@ -531,6 +531,14 @@ static inline int memcg_cache_id(struct mem_cgroup *memcg) return -1; } +static inline void memcg_get_cache_ids(void) +{ +} + +static inline void memcg_put_cache_ids(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 355e72b01ad6..3596f44875c1 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -570,6 +570,19 @@ static void disarm_sock_keys(struct mem_cgroup *memcg) static DEFINE_IDA(memcg_cache_ida); int memcg_nr_cache_ids; +/* Protects memcg_nr_cache_ids */ +static DECLARE_RWSEM(memcg_cache_ids_sem); + +void memcg_get_cache_ids(void) +{ + down_read(&memcg_cache_ids_sem); +} + +void memcg_put_cache_ids(void) +{ + up_read(&memcg_cache_ids_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 @@ -2558,6 +2571,7 @@ 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_ids_sem); size = 2 * (id + 1); if (size < MEMCG_CACHES_MIN_SIZE) @@ -2566,6 +2580,11 @@ static int memcg_alloc_cache_id(void) size = MEMCG_CACHES_MAX_SIZE; err = memcg_update_all_caches(size); + if (!err) + memcg_nr_cache_ids = size; + + up_write(&memcg_cache_ids_sem); + if (err) { ida_simple_remove(&memcg_cache_ida, id); return err; @@ -2578,16 +2597,6 @@ 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_nr_cache_ids = num; -} - struct memcg_kmem_cache_create_work { struct mem_cgroup *memcg; struct kmem_cache *cachep; diff --git a/mm/slab_common.c b/mm/slab_common.c index d6cf88c2739f..42bb22cb4219 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -169,8 +169,8 @@ 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; @@ -181,11 +181,8 @@ 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; } @@ -369,6 +366,7 @@ kmem_cache_create(const char *name, size_t size, size_t align, get_online_cpus(); get_online_mems(); + memcg_get_cache_ids(); mutex_lock(&slab_mutex); @@ -407,6 +405,7 @@ kmem_cache_create(const char *name, size_t size, size_t align, out_unlock: mutex_unlock(&slab_mutex); + memcg_put_cache_ids(); 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/
