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From: Eric Sandeen <sandeen@sandeen.net>
To: Smit Shah <getsmit@gmail.com>
Cc: linux-xfs@oss.sgi.com
Subject: Re: XFS Preallocate using ALLOCSP
Date: Tue, 16 Jun 2009 17:05:14 -0500	[thread overview]
Message-ID: <4A38171A.4080500@sandeen.net> (raw)
In-Reply-To: <8770d98c0906161442t634467bxe8b0f5c32b49502e@mail.gmail.com>

Smit Shah wrote:
> On 6/16/09, Felix Blyakher <felixb@sgi.com> wrote:

>>> but the write performance is going to suffer.
>> It's not clear why it should. Not doing preallocation doesn't
>> mean that there is no inode updates with every write. Why
>> would extent conversion be more expensive that creating the
>> space (extent) and updating the inode size for every write?
>> It'd interesting to reproduce your results. Any details on
>> your tests and the iometer usage?
> 
> Since fallocate uses the RESVSP cmd for xfs. And as given given for
> RESVSP in man page for xfsctl
> If the  XFS filesystem  is  configured to flag unwritten file extents,
> performance will be negatively affected when writing to preallocated
> space, since extra filesystem transactions are required to convert
> extent  flags  on  the  range  of  the  file  written.

And ext4 must do basically the same thing, as would any fs that flags
unwritten extents.

ext4 may convert more at a time, though, rather than leaving
"fragmented" written/unwritten/written/unwritten regions.

-Eric

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  reply	other threads:[~2009-06-16 22:04 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-06-16  0:18 XFS Preallocate using ALLOCSP Smit Shah
2009-06-16  2:00 ` Smit Shah
2009-06-16  3:34 ` Eric Sandeen
2009-06-16  6:44   ` Smit Shah
2009-06-16  7:34     ` Smit Shah
2009-06-16 15:16     ` Eric Sandeen
2009-06-16 16:42       ` Felix Blyakher
2009-06-16 17:28         ` Smit Shah
2009-06-16 17:32           ` Eric Sandeen
2009-06-16 21:38             ` Smit Shah
2009-06-17  1:04               ` Michael Monnerie
2009-06-16 17:41           ` Felix Blyakher
2009-06-16 21:42             ` Smit Shah
2009-06-16 22:05               ` Eric Sandeen [this message]
2009-06-16 22:32                 ` Felix Blyakher
2009-06-16 22:19               ` Smit Shah
2009-06-16 22:26               ` Felix Blyakher

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