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References: <1786ab030907281211x6e432ba6ha6afe9de73f24e0c@mail.gmail.com>
Date: Tue, 28 Jul 2009 14:49:38 -0700
Message-ID: <33307c790907281449k5e8d4f6cib2c93848f5ec2661@mail.gmail.com>
Subject: Re: Bug in kernel 2.6.31, Slow wb_kupdate writeout
From: Martin Bligh <mbligh@google.com>
To: Chad Talbott <ctalbott@google.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, wfg@mail.ustc.edu.cn,
       Michael Rubin <mrubin@google.com>, Andrew Morton <akpm@google.com>,
       sandeen@redhat.com
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> An interesting recent-ish change is "writeback: speed up writeback of
> big dirty files." ?When I revert the change to __sync_single_inode the
> problem appears to go away and background writeout proceeds at disk
> speed. ?Interestingly, that code is in the git commit [2], but not in
> the post to LKML. [3] ?This is may not be the fix, but it makes this
> test behave better.

I'm fairly sure this is not fixing the root cause - but putting it at the head
rather than the tail of the queue causes the error not to starve wb_kupdate
for nearly so long - as long as we keep the queue full, the bug is hidden.

M.
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