linux-kernel - Re: [patch 10/21] buffer heads: Support slab defrag

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Message-ID: <20080512002403.GP103491721@sgi.com>
Date:	Mon, 12 May 2008 10:24:03 +1000
From:	David Chinner <dgc@....com>
To:	Christoph Lameter <clameter@....com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, Mel Gorman <mel@...net.ie>,
	andi@...stfloor.org, Rik van Riel <riel@...hat.com>,
	Pekka Enberg <penberg@...helsinki.fi>, mpm@...enic.com
Subject: Re: [patch 10/21] buffer heads: Support slab defrag

On Fri, May 09, 2008 at 08:08:41PM -0700, Christoph Lameter wrote:
> Defragmentation support for buffer heads. We convert the references to
> buffers to struct page references and try to remove the buffers from
> those pages. If the pages are dirty then trigger writeout so that the
> buffer heads can be removed later.

Oh, no, please don't trigger more random single page writeback from
memory reclaim.  We shoul dbe killing the VM's use of ->writepage,
not encouraging it.

If you are going to clean bufferheads (or pages), please clean entire
mappings via ->writepages as it leads to far superior I/O patterns
and a far higher aggregate rate of page cleaning.....

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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