memcg: don't call memcg_update_all_caches if new cache id fits

memcg_update_all_caches grows arrays of per-memcg caches, so we only need
to call it when memcg_limited_groups_array_size is increased.  However,
currently we invoke it each time a new kmem-active memory cgroup is
created.  Then it just iterates over all slab_caches and does nothing
(memcg_update_cache_size returns immediately).

This patch fixes this insanity.  In the meantime it moves the code dealing
with id allocations to separate functions, memcg_alloc_cache_id and
memcg_free_cache_id.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 865e87c014d63e7e78189ca7d132af16030c5547..ef4fbc5e4ca3e0e1b005c344cfc195fda8a44a7e 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -649,11 +649,13 @@ int memcg_limited_groups_array_size;
 struct static_key memcg_kmem_enabled_key;
 EXPORT_SYMBOL(memcg_kmem_enabled_key);
 
+static void memcg_free_cache_id(int id);
+
 static void disarm_kmem_keys(struct mem_cgroup *memcg)
 {
        if (memcg_kmem_is_active(memcg)) {
                static_key_slow_dec(&memcg_kmem_enabled_key);
-               ida_simple_remove(&kmem_limited_groups, memcg->kmemcg_id);
+               memcg_free_cache_id(memcg->kmemcg_id);
        }
        /*
         * This check can't live in kmem destruction function,
@@ -2906,19 +2908,44 @@ int memcg_cache_id(struct mem_cgroup *memcg)
        return memcg ? memcg->kmemcg_id : -1;
 }
 
-static size_t memcg_caches_array_size(int num_groups)
+static int memcg_alloc_cache_id(void)
 {
-       ssize_t size;
-       if (num_groups <= 0)
-               return 0;
+       int id, size;
+       int err;
+
+       id = ida_simple_get(&kmem_limited_groups,
+                           0, MEMCG_CACHES_MAX_SIZE, GFP_KERNEL);
+       if (id < 0)
+               return id;
 
-       size = 2 * num_groups;
+       if (id < memcg_limited_groups_array_size)
+               return id;
+
+       /*
+        * There's no space for the new id in memcg_caches arrays,
+        * so we have to grow them.
+        */
+
+       size = 2 * (id + 1);
        if (size < MEMCG_CACHES_MIN_SIZE)
                size = MEMCG_CACHES_MIN_SIZE;
        else if (size > MEMCG_CACHES_MAX_SIZE)
                size = MEMCG_CACHES_MAX_SIZE;
 
-       return size;
+       mutex_lock(&memcg_slab_mutex);
+       err = memcg_update_all_caches(size);
+       mutex_unlock(&memcg_slab_mutex);
+
+       if (err) {
+               ida_simple_remove(&kmem_limited_groups, id);
+               return err;
+       }
+       return id;
+}
+
+static void memcg_free_cache_id(int id)
+{
+       ida_simple_remove(&kmem_limited_groups, id);
 }
 
 /*
@@ -2928,59 +2955,55 @@ static size_t memcg_caches_array_size(int num_groups)
  */
 void memcg_update_array_size(int num)
 {
-       if (num > memcg_limited_groups_array_size)
-               memcg_limited_groups_array_size = memcg_caches_array_size(num);
+       memcg_limited_groups_array_size = num;
 }
 
 int memcg_update_cache_size(struct kmem_cache *s, int num_groups)
 {
        struct memcg_cache_params *cur_params = s->memcg_params;
+       struct memcg_cache_params *new_params;
+       size_t size;
+       int i;
 
        VM_BUG_ON(!is_root_cache(s));
 
-       if (num_groups > memcg_limited_groups_array_size) {
-               int i;
-               struct memcg_cache_params *new_params;
-               ssize_t size = memcg_caches_array_size(num_groups);
+       size = num_groups * sizeof(void *);
+       size += offsetof(struct memcg_cache_params, memcg_caches);
 
-               size *= sizeof(void *);
-               size += offsetof(struct memcg_cache_params, memcg_caches);
-
-               new_params = kzalloc(size, GFP_KERNEL);
-               if (!new_params)
-                       return -ENOMEM;
-
-               new_params->is_root_cache = true;
+       new_params = kzalloc(size, GFP_KERNEL);
+       if (!new_params)
+               return -ENOMEM;
 
-               /*
-                * There is the chance it will be bigger than
-                * memcg_limited_groups_array_size, if we failed an allocation
-                * in a cache, in which case all caches updated before it, will
-                * have a bigger array.
-                *
-                * But if that is the case, the data after
-                * memcg_limited_groups_array_size is certainly unused
-                */
-               for (i = 0; i < memcg_limited_groups_array_size; i++) {
-                       if (!cur_params->memcg_caches[i])
-                               continue;
-                       new_params->memcg_caches[i] =
-                                               cur_params->memcg_caches[i];
-               }
+       new_params->is_root_cache = true;
 
-               /*
-                * Ideally, we would wait until all caches succeed, and only
-                * then free the old one. But this is not worth the extra
-                * pointer per-cache we'd have to have for this.
-                *
-                * It is not a big deal if some caches are left with a size
-                * bigger than the others. And all updates will reset this
-                * anyway.
-                */
-               rcu_assign_pointer(s->memcg_params, new_params);
-               if (cur_params)
-                       kfree_rcu(cur_params, rcu_head);
+       /*
+        * There is the chance it will be bigger than
+        * memcg_limited_groups_array_size, if we failed an allocation
+        * in a cache, in which case all caches updated before it, will
+        * have a bigger array.
+        *
+        * But if that is the case, the data after
+        * memcg_limited_groups_array_size is certainly unused
+        */
+       for (i = 0; i < memcg_limited_groups_array_size; i++) {
+               if (!cur_params->memcg_caches[i])
+                       continue;
+               new_params->memcg_caches[i] =
+                       cur_params->memcg_caches[i];
        }
+
+       /*
+        * Ideally, we would wait until all caches succeed, and only
+        * then free the old one. But this is not worth the extra
+        * pointer per-cache we'd have to have for this.
+        *
+        * It is not a big deal if some caches are left with a size
+        * bigger than the others. And all updates will reset this
+        * anyway.
+        */
+       rcu_assign_pointer(s->memcg_params, new_params);
+       if (cur_params)
+               kfree_rcu(cur_params, rcu_head);
        return 0;
 }
 
@@ -4181,23 +4204,12 @@ static int __memcg_activate_kmem(struct mem_cgroup *memcg,
        if (err)
                goto out;
 
-       memcg_id = ida_simple_get(&kmem_limited_groups,
-                                 0, MEMCG_CACHES_MAX_SIZE, GFP_KERNEL);
+       memcg_id = memcg_alloc_cache_id();
        if (memcg_id < 0) {
                err = memcg_id;
                goto out;
        }
 
-       /*
-        * Make sure we have enough space for this cgroup in each root cache's
-        * memcg_params.
-        */
-       mutex_lock(&memcg_slab_mutex);
-       err = memcg_update_all_caches(memcg_id + 1);
-       mutex_unlock(&memcg_slab_mutex);
-       if (err)
-               goto out_rmid;
-
        memcg->kmemcg_id = memcg_id;
        INIT_LIST_HEAD(&memcg->memcg_slab_caches);
 
@@ -4218,10 +4230,6 @@ static int __memcg_activate_kmem(struct mem_cgroup *memcg,
 out:
        memcg_resume_kmem_account();
        return err;
-
-out_rmid:
-       ida_simple_remove(&kmem_limited_groups, memcg_id);
-       goto out;
 }
 
 static int memcg_activate_kmem(struct mem_cgroup *memcg,