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authorVladimir Davydov <vdavydov@parallels.com>2015-02-12 14:59:01 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2015-02-12 18:54:09 -0800
commit05257a1a3dcc196c197714b5c9a8dd35b7f6aefc (patch)
tree063e4bafec04171990ce3f95f649a9e3c6dcd6a8 /mm
parentdbcf73e26cd0b3d66e6db65ab595e664a55e58ff (diff)
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')
-rw-r--r--mm/memcontrol.c29
-rw-r--r--mm/slab_common.c9
2 files changed, 23 insertions, 15 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;
diff --git a/mm/slab_common.c b/mm/slab_common.c
index f8899eedab68..23f5fcde6043 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();