linux-kernel - Re: [PATCH v3 3/4] limit nr

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Date:	Mon, 15 Aug 2011 15:32:17 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Pekka Enberg <penberg@...nel.org>
CC:	Dave Chinner <david@...morbit.com>,
	Glauber Costa <glommer@...allels.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"containers@...ts.linux-foundation.org" 
	<containers@...ts.linux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	Nick Piggin <npiggin@...nel.dk>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	James Bottomley <jbottomley@...allels.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v3 3/4] limit nr_dentries per superblock

On 08/15/2011 03:14 PM, Pekka Enberg wrote:
> Hi Pavel,
> 
> On Mon, Aug 15, 2011 at 2:05 PM, Pavel Emelyanov <xemul@...allels.com> wrote:
>> This will make sense, since the kernel memory management per-cgroup is one of the
>> things we'd live to have, but this particular idea will definitely not work in case
>> we keep the containers' files on one partition keeping each container in its own
>> chroot environment.
> 
> And you want a per-container dcache limit? 

To be more specific - we want to protect the node with >1 containers from one of
them growing the dcache infinitely. One of the solutions to this - per container
dcache limit.

> Will the containers share the same superblock? 

Yes, this is typical scenario for both OpenVZ and LXC now.

> Couldn't you simply do per-container "struct kmem_accounted_cache" in struct superblock?

If by this you mean "account for all the kmem associated with particular superblock" then
this is OK for us, but this can't be done in a simple

	if (used + size > limit)
		return -ENOMEM
	else {
		used += size;
		return 0;
	}

manner, since once we hit the limit we should shrink the unused dentries. And most of the
patches are about this.

>                         Pekka
> .
> 

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