[PATCH v10 02/16] memcg: consolidate callers of memcg_cache_id

[Glauber Costa <glommer@xxxxxxxxx>]

From: Glauber Costa <glommer@xxxxxxxxx>

Each caller of memcg_cache_id ends up sanitizing its parameters in its own way.
Now that the memcg_cache_id itself is more robust, we can consolidate this.

Also, as suggested by Michal, a special helper memcg_cache_idx is used when the
result is expected to be used directly as an array index to make sure we never
accesses in a negative index.

Signed-off-by: Glauber Costa <glommer@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
 mm/memcontrol.c | 49 +++++++++++++++++++++++++++++--------------------
 1 file changed, 29 insertions(+), 20 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 506ad46..f524332 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2941,6 +2941,30 @@ static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg)
 }
 
 /*
+ * helper for acessing a memcg's index. It will be used as an index in the
+ * child cache array in kmem_cache, and also to derive its name. This function
+ * will return -1 when this is not a kmem-limited memcg.
+ */
+int memcg_cache_id(struct mem_cgroup *memcg)
+{
+	if (!memcg || !memcg_can_account_kmem(memcg))
+		return -1;
+	return memcg->kmemcg_id;
+}
+
+/*
+ * This helper around memcg_cache_id is not intented for use outside memcg
+ * core. It is meant for places where the cache id is used directly as an array
+ * index
+ */
+static int memcg_cache_idx(struct mem_cgroup *memcg)
+{
+	int ret = memcg_cache_id(memcg);
+	BUG_ON(ret < 0);
+	return ret;
+}
+
+/*
  * This is a bit cumbersome, but it is rarely used and avoids a backpointer
  * in the memcg_cache_params struct.
  */
@@ -2950,7 +2974,7 @@ static struct kmem_cache *memcg_params_to_cache(struct memcg_cache_params *p)
 
 	VM_BUG_ON(p->is_root_cache);
 	cachep = p->root_cache;
-	return cachep->memcg_params->memcg_caches[memcg_cache_id(p->memcg)];
+	return cachep->memcg_params->memcg_caches[memcg_cache_idx(p->memcg)];
 }
 
 #ifdef CONFIG_SLABINFO
@@ -3055,18 +3079,6 @@ void memcg_cache_list_add(struct mem_cgroup *memcg, struct kmem_cache *cachep)
 }
 
 /*
- * helper for acessing a memcg's index. It will be used as an index in the
- * child cache array in kmem_cache, and also to derive its name. This function
- * will return -1 when this is not a kmem-limited memcg.
- */
-int memcg_cache_id(struct mem_cgroup *memcg)
-{
-	if (!memcg || !memcg_can_account_kmem(memcg))
-		return -1;
-	return memcg->kmemcg_id;
-}
-
-/*
  * This ends up being protected by the set_limit mutex, during normal
  * operation, because that is its main call site.
  *
@@ -3225,7 +3237,7 @@ void memcg_release_cache(struct kmem_cache *s)
 		goto out;
 
 	memcg = s->memcg_params->memcg;
-	id  = memcg_cache_id(memcg);
+	id  = memcg_cache_idx(memcg);
 
 	root = s->memcg_params->root_cache;
 	root->memcg_params->memcg_caches[id] = NULL;
@@ -3388,9 +3400,7 @@ static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
 	struct kmem_cache *new_cachep;
 	int idx;
 
-	BUG_ON(!memcg_can_account_kmem(memcg));
-
-	idx = memcg_cache_id(memcg);
+	idx = memcg_cache_idx(memcg);
 
 	mutex_lock(&memcg_cache_mutex);
 	new_cachep = cachep->memcg_params->memcg_caches[idx];
@@ -3563,10 +3573,9 @@ struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep,
 	rcu_read_lock();
 	memcg = mem_cgroup_from_task(rcu_dereference(current->mm->owner));
 
-	if (!memcg_can_account_kmem(memcg))
-		goto out;
-
 	idx = memcg_cache_id(memcg);
+	if (idx < 0)
+		return cachep;
 
 	/*
 	 * barrier to mare sure we're always seeing the up to date value.  The
-- 
1.8.2.1

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