linux-kernel - Re: [PATCH] ext2: avoid needless discard of preallocated blocks

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Message-Id: <1156087499.23756.39.camel@laptopd505.fenrus.org>
Date:	Sun, 20 Aug 2006 17:24:59 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	Ron Yorston <rmy@...ress.co.uk>
Cc:	Val Henson <val.henson@...il.com>, akpm@...l.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] ext2: avoid needless discard of preallocated blocks

On Sun, 2006-08-20 at 12:48 +0100, Ron Yorston wrote:
> Andrew Morton <akpm@...l.org> wrote:
> >Been there, done that.  The problem was that hanging onto the preallocation
> >will cause separate files to have up-to-seven-block gaps between them.  So
> >if you put a large number of small files in the same directory, the time to
> >read them all back is quite significantly impacted: they cover a lot more
> >disk.
> 
> The preallocation is only held while the file is open, so there will only
> be gaps between files that are open simultaneously.  If they're created
> sequentially there will be no gap.
> 
> This issue exists even with the current code.
> 
> The patch will have a small effect.  With the current code an open file
> will lose its preallocation when some other process touches the inode.
> In that case a subsequently created file will follow without a gap.  As
> soon as the open file is written to, though, it gets a new preallocation.
> -

maybe porting the reservation code to ext2 (as Val has done) is a nicer
long term solution..

-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com

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