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memcg: add rwsem to synchronize against memcg_caches arrays relocation

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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>
This commit is contained in:
Vladimir Davydov 2015-02-12 14:59:01 -08:00 committed by Linus Torvalds
parent dbcf73e26c
commit 05257a1a3d
3 changed files with 33 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
include/linux/memcontrol.h
View File

@ -399,6 +399,8 @@ 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
@ -434,8 +436,6 @@ 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);
@ -569,6 +569,14 @@ 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)
{

29
mm/memcontrol.c
View File

@ -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;

9
mm/slab_common.c
View File

@ -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();