linux-kernel - Re: [PATCH v2 04/11] kmem accounting basic infrastructure

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Message-ID: <502BC1B1.3010807@parallels.com>
Date:	Wed, 15 Aug 2012 19:35:13 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Michal Hocko <mhocko@...e.cz>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, <cgroups@...r.kernel.org>,
	<devel@...nvz.org>, Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<kamezawa.hiroyu@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>
Subject: Re: [PATCH v2 04/11] kmem accounting basic infrastructure

On 08/15/2012 07:34 PM, Christoph Lameter wrote:
> On Wed, 15 Aug 2012, Glauber Costa wrote:
> 
>> On 08/15/2012 06:47 PM, Christoph Lameter wrote:
>>> On Wed, 15 Aug 2012, Michal Hocko wrote:
>>>
>>>>> That is not what the kernel does, in general. We assume that if he wants
>>>>> that memory and we can serve it, we should. Also, not all kernel memory
>>>>> is unreclaimable. We can shrink the slabs, for instance. Ying Han
>>>>> claims she has patches for that already...
>>>>
>>>> Are those patches somewhere around?
>>>
>>> You can already shrink the reclaimable slabs (dentries / inodes) via
>>> calls to the subsystem specific shrinkers. Did Ying Han do anything to
>>> go beyond that?
>>>
>> That is not enough for us.
>> We would like to make sure that the objects being discarded belong to
>> the memcg which is under pressure. We don't need to be perfect here, and
>> an occasional slip is totally fine. But if in general, shrinking from
>> memcg A will mostly wipe out objects from memcg B, we harmed the system
>> in return for nothing good.
> 
> How can you figure out which objects belong to which memcg? The ownerships
> of dentries and inodes is a dubious concept already.
> 

Remember we copy over the metadata and create copies of the caches
per-memcg. Therefore, a dentry belongs to a memcg if it was allocated
from the slab pertaining to that memcg.

It is not 100 % accurate, but it is good enough.
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