From: Dave Chinner <david@fromorbit.com>
To: Brian Foster <bfoster@redhat.com>
Cc: xfs@oss.sgi.com
Subject: Re: [PATCH v3 1/2] xfs: replace global xfslogd wq with per-mount wq
Date: Fri, 28 Nov 2014 13:49:45 +1100 [thread overview]
Message-ID: <20141128024945.GC16151@dastard> (raw)
In-Reply-To: <1415906641-43587-2-git-send-email-bfoster@redhat.com>
On Thu, Nov 13, 2014 at 02:24:00PM -0500, Brian Foster wrote:
> The xfslogd workqueue is a global, single-job workqueue for buffer ioend
> processing. This means we allow for a single work item at a time for all
> possible XFS mounts on a system. fsstress testing in loopback XFS over
> XFS configurations has reproduced xfslogd deadlocks due to the single
> threaded nature of the queue and dependencies introduced between the
> separate XFS instances by online discard (-o discard).
>
> Discard over a loopback device converts the discard request to a hole
> punch (fallocate) on the underlying file. Online discard requests are
> issued synchronously and from xfslogd context in XFS, hence the xfslogd
> workqueue is blocked in the upper fs waiting on a hole punch request to
> be servied in the lower fs. If the lower fs issues I/O that depends on
> xfslogd to complete, both filesystems end up hung indefinitely. This is
> reproduced reliabily by generic/013 on XFS->loop->XFS test devices with
> the '-o discard' mount option.
>
> Further, docker implementations appear to use this kind of configuration
> for container instance filesystems by default (container fs->dm->
> loop->base fs) and therefore are subject to this deadlock when running
> on XFS.
>
> Replace the global xfslogd workqueue with a per-mount variant. This
> guarantees each mount access to a single worker and prevents deadlocks
> due to inter-fs dependencies introduced by discard. Since the queue is
> only responsible for buffer iodone processing at this point in time,
> rename xfslogd to xfs-buf.
>
> Signed-off-by: Brian Foster <bfoster@redhat.com>
Looks good. I'll take this as is and we can refine the way we point
to the workqueue in the patches that separate the log buffer
completions...
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
_______________________________________________
xfs mailing list
xfs@oss.sgi.com
http://oss.sgi.com/mailman/listinfo/xfs
next prev parent reply other threads:[~2014-11-28 2:49 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-13 19:23 [PATCH v3 0/2] xfs: split up xfslogd global workqueue Brian Foster
2014-11-13 19:24 ` [PATCH v3 1/2] xfs: replace global xfslogd wq with per-mount wq Brian Foster
2014-11-28 2:49 ` Dave Chinner [this message]
2014-11-13 19:24 ` [PATCH RFC v3 2/2] xfs: split metadata and log buffer completion to separate workqueues Brian Foster
2014-11-28 2:48 ` Dave Chinner
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=20141128024945.GC16151@dastard \
--to=david@fromorbit.com \
--cc=bfoster@redhat.com \
--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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.