From: Mark Tinguely <tinguely@sgi.com>
To: Jan Kara <jack@suse.cz>
Cc: xfs@oss.sgi.com
Subject: Re: [PATCH v2] xfs: Avoid pathological backwards allocation
Date: Tue, 16 Apr 2013 10:41:58 -0500 [thread overview]
Message-ID: <516D7146.8010308@sgi.com> (raw)
In-Reply-To: <1365710996-16439-1-git-send-email-jack@suse.cz>
On 04/11/13 15:09, 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.
>
Looks good. I also agree this should wait for Linux 3.11.
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
_______________________________________________
xfs mailing list
xfs@oss.sgi.com
http://oss.sgi.com/mailman/listinfo/xfs
next prev parent reply other threads:[~2013-04-16 15:41 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 [this message]
2013-05-20 13:56 ` Jan Kara
2013-05-20 14:57 ` Mark Tinguely
2013-05-20 18:10 ` Ben Myers
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=516D7146.8010308@sgi.com \
--to=tinguely@sgi.com \
--cc=jack@suse.cz \
--cc=xfs@oss.sgi.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox