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Date: Sat, 7 Nov 2015 14:55:19 -0600 (CST)
From: Christoph Lameter <cl@linux.com>
Subject: Re: [PATCH V2 2/2] slub: add missing kmem cgroup support to
 kmem_cache_free_bulk
In-Reply-To: <20151107202548.GO29259@esperanza>
Message-ID: <alpine.DEB.2.20.1511071453460.9141@east.gentwo.org>
References: <20151105153704.1115.10475.stgit@firesoul> <20151105153756.1115.41409.stgit@firesoul> <20151105162514.GI29259@esperanza> <20151107175338.12a0368b@redhat.com> <20151107202548.GO29259@esperanza>
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To: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>, linux-mm@kvack.org, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Andrew Morton <akpm@linux-foundation.org>

On Sat, 7 Nov 2015, Vladimir Davydov wrote:

> Hmm, I thought that a bunch of objects allocated using
> kmem_cache_alloc_bulk must be freed using kmem_cache_free_bulk. If it
> does not hold, i.e. if one can allocate an array of objects one by one
> using kmem_cache_alloc and then batch-free them using
> kmem_cache_free_bulk, then my proposal is irrelevant.

Nope they can be allocated and freed in multiple ways.

> > With my limited mem cgroups, it looks like memcg works on the slab-page
> > level?
>
> Yes, a memcg has its private copy of each global kmem cache it attempted
> to use, which implies that all objects on the same slab-page must belong
> to the same memcg.

Every memcg duplicates all slab caches and thus these are separate caches.
Bulk freeing to a mixture of cgroups caches does not work.

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