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From: Miklos Szeredi <miklos@szeredi.hu>
To: riel@redhat.com
Cc: akpm@linux-foundation.org, miklos@szeredi.hu,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: dirty balancing deadlock
Date: Sun, 18 Feb 2007 23:54:06 +0100	[thread overview]
Message-ID: <E1HIuv0-0005Cy-00@dorka.pomaz.szeredi.hu> (raw)
In-Reply-To: <45D8C43A.3060800@redhat.com> (message from Rik van Riel on Sun, 18 Feb 2007 16:25:14 -0500)

> Andrew Morton wrote:
> > On Sun, 18 Feb 2007 19:28:18 +0100 Miklos Szeredi <miklos@szeredi.hu> wrote:
> > 
> >> I was testing the new fuse shared writable mmap support, and finding
> >> that bash-shared-mapping deadlocks (which isn't so strange ;).  What
> >> is more strange is that this is not an OOM situation at all, with
> >> plenty of free and cached pages.
> >>
> >> A little more investigation shows that a similar deadlock happens
> >> reliably with bash-shared-mapping on a loopback mount, even if only
> >> half the total memory is used.
> >>
> >> The cause is slightly different in the two cases:
> >>
> >>   - loopback mount: allocation by the underlying filesystem is stalled
> >>     on throttle_vm_writeout()
> >>
> >>   - fuse-loop: page dirtying on the underlying filesystem is stalled on
> >>     balance_dirty_pages()
> >>
> >> In both cases the underlying fs is totally innocent, with no
> >> dirty/writback pages, yet it's waiting for the global dirty+writeback
> >> to go below the threshold, which obviously won't, until the
> >> allocation/dirtying succeeds.
> >>
> >> I'm not quite sure what the solution is, and asking for thoughts.
> > 
> > But....  these things don't just throttle.  They also perform large amounts
> > of writeback, which causes the dirty levels to subside.
> > 
> >>From your description it appears that this writeback isn't happening, or
> > isn't working.  How come?
> 
> Is the fuse daemon trying to do writeback to itself, perhaps?
> 
> That is, trying to write out data to the FUSE filesystem, for which
> it is also the server.

No.  It's trying to write out data to a different filesystem.

Trying to write out data to itself very obviously deadlocks, but that
doesn't affect anything beside the stupid filesystem itself, and there
are mechanisms for aborting such a situation (forced umount, abort
through fuse-control filesystem).

Miklos

  reply	other threads:[~2007-02-18 22:54 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-18 18:28 Miklos Szeredi
2007-02-18 20:53 ` Andrew Morton
2007-02-18 21:25   ` Rik van Riel
2007-02-18 22:54     ` Miklos Szeredi [this message]
2007-02-18 22:50   ` Miklos Szeredi
2007-02-18 22:59     ` Andrew Morton
2007-02-18 23:22       ` Miklos Szeredi
2007-02-18 23:59         ` Andrew Morton
2007-02-19  0:25           ` Miklos Szeredi
2007-02-19  0:30             ` Miklos Szeredi
2007-02-19  0:45             ` Miklos Szeredi
2007-02-19  0:45             ` Chris Mason
2007-02-19  0:54               ` Miklos Szeredi
2007-02-19  1:01                 ` Chris Mason
2007-02-19  1:14                   ` Miklos Szeredi
2007-02-20  0:16                     ` Chris Mason
2007-02-20  8:53                       ` Miklos Szeredi
2007-02-19 17:11           ` Miklos Szeredi
2007-02-19 23:12             ` Miklos Szeredi
2007-02-20  0:13             ` Chris Mason
2007-02-20  8:47               ` Miklos Szeredi
2007-02-20 11:30                 ` Chris Mason
2007-02-21 21:36             ` Andrew Morton
2007-02-22  7:42               ` Miklos Szeredi
2007-02-22  7:55                 ` Andrew Morton
2007-02-22  8:02                   ` Miklos Szeredi

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