linux-kernel - Re: [PATCH v5 14/14] Add documentation about the kmem controller

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Date:	Tue, 16 Oct 2012 18:25:06 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Glauber Costa <glommer@...allels.com>
cc:	linux-mm@...ck.org, cgroups@...r.kernel.org,
	Mel Gorman <mgorman@...e.de>, Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	kamezawa.hiroyu@...fujitsu.com,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>, devel@...nvz.org,
	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...hat.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [PATCH v5 14/14] Add documentation about the kmem controller

On Tue, 16 Oct 2012, Glauber Costa wrote:

>
> + memory.kmem.limit_in_bytes      # set/show hard limit for kernel memory
> + memory.kmem.usage_in_bytes      # show current kernel memory allocation
> + memory.kmem.failcnt             # show the number of kernel memory usage hits limits
> + memory.kmem.max_usage_in_bytes  # show max kernel memory usage recorded

Does it actually make sense to limit kernel memory? The user generally has
no idea how much kernel memory a process is using and kernel changes can
change the memory footprint. Given the fuzzy accounting in the kernel a
large cache refill (if someone configures the slab batch count to be
really big f.e.) can account a lot of memory to the wrong cgroup. The
allocation could fail.

Limiting the total memory use of a process (U+K) would make more sense I
guess. Only U is probably sufficient? In what way would a limitation on
kernel memory in use be good?

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