linux-kernel - Re: Slab Fragmentation Reduction V15

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Message-ID: <20100130104812.GE29555@one.firstfloor.org>
Date:	Sat, 30 Jan 2010 11:48:12 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Dave Chinner <david@...morbit.com>,
	Rik van Riel <riel@...hat.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	akpm@...ux-foundation.org, Miklos Szeredi <miklos@...redi.hu>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Hugh Dickins <hugh@...itas.com>, linux-kernel@...r.kernel.org,
	viro@...IV.linux.org.uk
Subject: Re: Slab Fragmentation Reduction V15

On Fri, Jan 29, 2010 at 02:49:31PM -0600, Christoph Lameter wrote:
> This patchset was first proposed in the beginning of 2007. It was almost merged
> in 2008 when last minute objections arose in the way this interacts with
> filesystem objects (inode/dentry).
> 
> Andi has asked that we reconsider this issue. So I have updated the patchset

Thanks for reposting.

My motivation here is to improve hwpoison soft offlining, but I think
having this would be a general improvement.

> to apply against current upstream (and also -next with a special patch
> at the end). The issues with icache/dentry locking remain. In order
> for this to be merged we would have to come up with a revised dentry/inode
> locking code that can
> 
> 	1. Establish a reference to an dentry/inode so that it is pinned.
>            Hopefully in a way that is not too expensive (i.e. no superblock
>            lock)
> 
> 	2. A means to free a dentry/inode objects from the VM reclaim context.


Al, do you have a suggestions on a good way to do that?

I guess the problem could be simplified by ignoring dentries in "unusual"
states?

> The other objection against this patchset was that it does not support
> reclaim through SLAB. It is possible to add this type of support to SLAB too

I think not supporting SLAB/SLOB is fine.

-Andi
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