linux-kernel - Re: [PATCH 11/15] readahead: dont do start-of-file readahead after lseek()

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Message-ID: <4B86FCDE.1010201@redhat.com>
Date:	Thu, 25 Feb 2010 17:42:38 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Clemens Ladisch <clemens@...isch.de>,
	Olivier Galibert <galibert@...ox.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com>,
	Matt Mackall <mpm@...enic.com>, Nick Piggin <npiggin@...e.de>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/15] readahead: dont do start-of-file readahead after
 lseek()

On 02/23/2010 10:10 PM, Wu Fengguang wrote:
> Some applications (eg. blkid, id3tool etc.) seek around the file
> to get information. For example, blkid does
> 	     seek to	0
> 	     read	1024
> 	     seek to	1536
> 	     read	16384
>
> The start-of-file readahead heuristic is wrong for them, whose
> access pattern can be identified by lseek() calls.
>
> So test-and-set a READAHEAD_LSEEK flag on lseek() and don't
> do start-of-file readahead on seeing it. Proposed by Linus.
>
> Acked-by: Linus Torvalds<torvalds@...ux-foundation.org>
> Signed-off-by: Wu Fengguang<fengguang.wu@...el.com>

Acked-by: Rik van Riel <riel@...hat.com>
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