linux-kernel - Re: inodes: Support generic defragmentation

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Date:	Thu, 4 Feb 2010 11:13:15 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Nick Piggin <npiggin@...e.de>
cc:	Dave Chinner <david@...morbit.com>, tytso@....edu,
	Andi Kleen <andi@...stfloor.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	Alexander Viro <viro@....linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Christoph Lameter <clameter@....com>,
	Rik van Riel <riel@...hat.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	akpm@...ux-foundation.org, Nick Piggin <nickpiggin@...oo.com.au>,
	Hugh Dickins <hugh@...itas.com>, linux-kernel@...r.kernel.org
Subject: Re: inodes: Support generic defragmentation

On Thu, 4 Feb 2010, Nick Piggin wrote:

> Well what I described is to do the slab pinning from the reclaim path
> (rather than from slab calling into the subsystem). All slab locking
> basically "innermost", so you can pretty much poke the slab layer as
> much as you like from the subsystem.

Reclaim/defrag is called from the reclaim path (of the VM). We could
enable a call from the fs reclaim code into the slab. But how would this
work?

> After that, LRU on slabs should be fairly easy. Slab could provide a
> private per-slab pointer for example that is managed by the caller.
> Subsystem can then call into slab to find the objects.

Sure with some minor changes we could have a call that is giving you the
list of neighboring objects in a slab, while locking it? Then you can look
at the objects and decide which ones can be tossed and then do another
call to release the objects and unlock the slab.



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