linux-kernel - Re: [PATCH -mm 1/4] sl[au]b: do not charge large allocations to memcg

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Date:	Thu, 27 Mar 2014 11:34:10 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Michal Hocko <mhocko@...e.cz>, <glommer@...il.com>
CC:	<akpm@...ux-foundation.org>, <hannes@...xchg.org>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<devel@...nvz.org>, Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>
Subject: Re: [PATCH -mm 1/4] sl[au]b: do not charge large allocations to memcg

Hi Michal,

On 03/27/2014 01:53 AM, Michal Hocko wrote:
> On Wed 26-03-14 19:28:04, Vladimir Davydov wrote:
>> We don't track any random page allocation, so we shouldn't track kmalloc
>> that falls back to the page allocator.
> Why did we do that in the first place? d79923fad95b (sl[au]b: allocate
> objects from memcg cache) didn't tell me much.

I don't know, we'd better ask Glauber about that.

> How is memcg_kmem_skip_account removal related?

The comment this patch removes along with the memcg_kmem_skip_account
check explains that pretty well IMO. In short, we only use
memcg_kmem_skip_account to prevent kmalloc's from charging, which is
crucial for recursion-avoidance in memcg_kmem_get_cache. Since we don't
charge pages allocated from a root (not per-memcg) cache, from the first
glance it would be enough to check for memcg_kmem_skip_account only in
memcg_kmem_get_cache and return the root cache if it's set. However, for
we can also kmalloc w/o issuing memcg_kmem_get_cache (kmalloc_large), we
also need this check in memcg_kmem_newpage_charge. This patch removes
kmalloc_large accounting, so we don't need this check anymore.

Thanks.
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