linux-kernel - Re: [PATCH v3 04/13] kmem accounting basic infrastructure

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Message-ID: <20120926163648.GO16296@google.com>
Date:	Wed, 26 Sep 2012 09:36:48 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Glauber Costa <glommer@...allels.com>,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	kamezawa.hiroyu@...fujitsu.com, devel@...nvz.org,
	linux-mm@...ck.org, Suleiman Souhlal <suleiman@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v3 04/13] kmem accounting basic infrastructure

Hello, Michal, Glauber.

On Wed, Sep 26, 2012 at 04:03:47PM +0200, Michal Hocko wrote:
> Haven't we already discussed that a new memcg should inherit kmem_accounted
> from its parent for use_hierarchy?
> Say we have
> root
> |
> A (kmem_accounted = 1, use_hierachy = 1)
>  \
>   B (kmem_accounted = 0)
>    \
>     C (kmem_accounted = 1)
> 
> B find's itself in an awkward situation becuase it doesn't want to
> account u+k but it ends up doing so becuase C.

Do we really want this level of flexibility?  What's wrong with a
global switch at the root?  I'm not even sure we want this to be
optional at all.  The only reason I can think of is that it might
screw up some configurations in use which are carefully crafted to
suit userland-only usage but for that isn't what we need a transition
plan rather than another ultra flexible config option that not many
really understand the implication of?

In the same vein, do we really need both .kmem_accounted and config
option?  If someone is turning on MEMCG, just include kmem accounting.

Thanks.

-- 
tejun
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