From: Mark Tinguely <tinguely@sgi.com>
To: Jan Kara <jack@suse.cz>
Cc: dchinner@redhat.com, xfs@oss.sgi.com
Subject: Re: [PATCH v2] xfs: Avoid pathological backwards allocation
Date: Mon, 20 May 2013 09:57:36 -0500 [thread overview]
Message-ID: <519A39E0.1020309@sgi.com> (raw)
In-Reply-To: <20130520135607.GA11502@quack.suse.cz>
On 05/20/13 08:56, Jan Kara wrote:
> On Thu 11-04-13 22:09:56, Jan Kara wrote:
>> Writing a large file using direct IO in 16 MB chunks sometimes results
>> in a pathological allocation pattern where 16 MB chunks of large free
>> extent are allocated to a file in a reversed order. So extents of a file
>> look for example as:
>>
>> ext logical physical expected length flags
>> 0 0 13 4550656
>> 1 4550656 188136807 4550668 12562432
>> 2 17113088 200699240 200699238 622592
>> 3 17735680 182046055 201321831 4096
>> 4 17739776 182041959 182050150 4096
>> 5 17743872 182037863 182046054 4096
>> 6 17747968 182033767 182041958 4096
>> 7 17752064 182029671 182037862 4096
>> ...
>> 6757 45400064 154381644 154389835 4096
>> 6758 45404160 154377548 154385739 4096
>> 6759 45408256 252951571 154381643 73728 eof
>>
>> This happens because XFS_ALLOCTYPE_THIS_BNO allocation fails (the last
>> extent in the file cannot be further extended) so we fall back to
>> XFS_ALLOCTYPE_NEAR_BNO allocation which picks end of a large free
>> extent as the best place to continue the file. Since the chunk at the
>> end of the free extent again cannot be further extended, this behavior
>> repeats until the whole free extent is consumed in a reversed order.
>>
>> For data allocations this backward allocation isn't beneficial so make
>> xfs_alloc_compute_diff() pick start of a free extent instead of its end
>> for them. That avoids the backward allocation pattern.
>>
>> See thread at http://oss.sgi.com/archives/xfs/2013-03/msg00144.html for
>> more details about the reproduction case and why this solution was
>> chosen.
>>
>> Based on idea by Dave Chinner<dchinner@redhat.com>.
>>
>> CC: Dave Chinner<dchinner@redhat.com>
>> Reviewed-by: Dave Chinner<dchinner@redhat.com>
>> Signed-off-by: Jan Kara<jack@suse.cz>
>> ---
>> fs/xfs/xfs_alloc.c | 24 ++++++++++++++++++------
>> 1 files changed, 18 insertions(+), 6 deletions(-)
>>
>> v2: Updated comment and commit description.
> Could anybody pull this patch into XFS tree? I don't see it there...
>
> Honza
Sorry, a miscommunication on my part that this belonged in the dev tree
but not in the for Linus pull for Linux 3.10.
--Mark.
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next prev parent reply other threads:[~2013-05-20 14:57 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-11 20:09 [PATCH v2] xfs: Avoid pathological backwards allocation Jan Kara
2013-04-16 15:41 ` Mark Tinguely
2013-05-20 13:56 ` Jan Kara
2013-05-20 14:57 ` Mark Tinguely [this message]
2013-05-20 18:10 ` Ben Myers
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