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author | Vladimir Davydov <vdavydov@parallels.com> | 2015-02-12 14:59:01 -0800 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2015-02-12 18:54:09 -0800 |
commit | 05257a1a3dcc196c197714b5c9a8dd35b7f6aefc (patch) | |
tree | 063e4bafec04171990ce3f95f649a9e3c6dcd6a8 /mm/memcontrol.c | |
parent | dbcf73e26cd0b3d66e6db65ab595e664a55e58ff (diff) | |
download | linux-05257a1a3dcc196c197714b5c9a8dd35b7f6aefc.tar.gz linux-05257a1a3dcc196c197714b5c9a8dd35b7f6aefc.tar.bz2 linux-05257a1a3dcc196c197714b5c9a8dd35b7f6aefc.zip |
memcg: add rwsem to synchronize against memcg_caches arrays relocation
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 <vdavydov@parallels.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Greg Thelen <gthelen@google.com>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memcontrol.c')
-rw-r--r-- | mm/memcontrol.c | 29 |
1 files changed, 19 insertions, 10 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 8608fa543b84..6706e5fa5ac0 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -544,6 +544,19 @@ 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 @@ -2549,6 +2562,7 @@ 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) @@ -2557,6 +2571,11 @@ 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; @@ -2569,16 +2588,6 @@ 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; |