From: Dave Chinner <david@fromorbit.com>
To: Ivan.Novick@emc.com
Cc: Timothy.Heath@emc.com, xfs@oss.sgi.com
Subject: Re: allocsize mount option
Date: Wed, 29 Sep 2010 10:31:10 +1000 [thread overview]
Message-ID: <20100929003110.GH5665@dastard> (raw)
In-Reply-To: <C8C787CA.44AA%ivan.novick@emc.com>
On Tue, Sep 28, 2010 at 02:53:46PM -0400, Ivan.Novick@emc.com wrote:
> Hi all,
>
> According to the documentation the allocsize mount option: "Sets the
> buffered I/O end-of-file preallocation size when doing delayed allocation
> writeout"
>
> Will this value limit "extent" sizes to be be no smaller than the allocsize?
No - it's specualtive preallocation.
> I have set the following mount options:
> (rw,noatime,nodiratime,logbufs=8,allocsize=512m)
/me wishes he could run a sed script across the internet.
noatime implies nodiratime, and logbufs=8 is the default, so you
only need "noatime,allocsize=512m"
> And yet, depending on the workload, the extent sizes are often 1 or 2 orders
> of magnitude lower than 512 MB ...
It's speculative and there's no guarantee that it can find a big
enough extent to complete the full allocsize allocation. Also, when
you close the file the speculative allocation beyond EOF is
truncated away. This is a particular problem with NFS servers.
> If I wanted to do further reading on the subject, can someone point me to an
> approximate location in the code where the size of a newly created extent is
> determined?
Start here:
fs/xfs/xfs_iomap.c::xfs_iomap_write_delay()
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
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next prev parent reply other threads:[~2010-09-29 0:30 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-28 18:53 allocsize mount option Ivan.Novick
2010-09-29 0:31 ` Dave Chinner [this message]
-- strict thread matches above, loose matches on Subject: below --
2011-01-20 20:41 Peter Vajgel
2011-01-21 0:48 ` Dave Chinner
2010-01-24 6:44 Gim Leong Chin
2010-01-15 3:08 Gim Leong Chin
2010-01-14 17:25 Gim Leong Chin
2010-01-14 17:42 ` Eric Sandeen
2010-01-14 23:28 ` Dave Chinner
2010-01-13 9:42 Gim Leong Chin
2010-01-13 10:50 ` Dave Chinner
2010-01-11 17:25 Gim Leong Chin
2010-01-11 18:16 ` Eric Sandeen
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