linux-kernel - Re: [PATCH v2 02/13] memcg: Kernel memory accounting infrastructure.

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Date:	Tue, 13 Mar 2012 21:31:40 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Greg Thelen <gthelen@...gle.com>
CC:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Suleiman Souhlal <ssouhlal@...eBSD.org>,
	<cgroups@...r.kernel.org>, <suleiman@...gle.com>,
	<penberg@...nel.org>, <cl@...ux.com>, <yinghan@...gle.com>,
	<hughd@...gle.com>, <peterz@...radead.org>,
	<dan.magenheimer@...cle.com>, <hannes@...xchg.org>,
	<mgorman@...e.de>, <James.Bottomley@...senPartnership.com>,
	<linux-mm@...ck.org>, <devel@...nvz.org>,
	<linux-kernel@...r.kernel.org>, <rientjes@...gle.com>
Subject: Re: [PATCH v2 02/13] memcg: Kernel memory accounting infrastructure.

On 03/13/2012 09:00 PM, Greg Thelen wrote:
> Glauber Costa<glommer@...allels.com>  writes:
>> 2) For the kernel itself, we are mostly concerned that a malicious container may
>> pin into memory big amounts of kernel memory which is, ultimately,
>> unreclaimable. In particular, with overcommit allowed scenarios, you can fill
>> the whole physical memory (or at least a significant part) with those objects,
>> well beyond your softlimit allowance, making the creation of further containers
>> impossible.
>> With user memory, you can reclaim the cgroup back to its place. With kernel
>> memory, you can't.
>
> In overcommit situations the page allocator starts failing even though
> memcg page can charge pages.
If you overcommit mem+swap, yes. If you overcommit mem, no: reclaim 
happens first. And we don't have that option with pinned kernel memory.

Of course you *can* run your system without swap, but the whole thing 
exists exactly because there is a large enough # of ppl who wants to be 
able to overcommit their physical memory, without failing allocations.

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