linux-kernel - Re: [PATCH 10/11] readahead: dont do start-of-file readahead after lseek()

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Date:	Tue, 2 Feb 2010 09:39:38 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/11] readahead: dont do start-of-file readahead after
 lseek()



On Tue, 2 Feb 2010, 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.
> 
> CC: Linus Torvalds <torvalds@...ux-foundation.org> 
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>

Acked-by: Linus Torvalds <torvalds@...ux-foundation.org>

		Linus
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