[Devel] [PATCH 3/8] memcg, slab: never try to merge memcg caches

[Vladimir Davydov]

On 02/06/2014 06:07 PM, Michal Hocko wrote:
> On Tue 04-02-14 19:27:19, Vladimir Davydov wrote:
> [...]
>> What does this patch change? Actually, it introduces no functional
>> changes - it only remove the code trying to find an alias for a memcg
>> cache, because it will fail anyway. So this is rather a cleanup.
> But this also means that two different memcgs might share the same cache
> and so the pages for that cache, no?

No, because in this patch I explicitly forbid to merge memcg caches by
this hunk:

@@ -200,9 +200,11 @@ kmem_cache_create_memcg(struct mem_cgroup *memcg,
const char *name, size_t size,
      */
     flags &= CACHE_CREATE_MASK;
 
-    s = __kmem_cache_alias(memcg, name, size, align, flags, ctor);
-    if (s)
-        goto out_unlock;
+    if (!memcg) {
+        s = __kmem_cache_alias(name, size, align, flags, ctor);
+        if (s)
+            goto out_unlock;
+    }

Thanks.

> Actually it would depend on timing
> because a new page would be chaged for the current allocator.
>
> cachep->memcg_params->memcg == memcg would prevent from such a merge
> previously AFAICS, or am I still confused?