linux-kernel - Re: [PATCH 3/8] memcg, slab: never try to merge memcg caches

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Date:	Thu, 6 Feb 2014 18:15:50 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	<akpm@...ux-foundation.org>, <rientjes@...gle.com>,
	<penberg@...nel.org>, <cl@...ux.com>, <glommer@...il.com>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<devel@...nvz.org>
Subject: Re: [PATCH 3/8] memcg, slab: never try to merge memcg caches

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?

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