linux-kernel - Re: Bug in kernel 2.6.31, Slow wb

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Message-ID: <33307c790907281449k5e8d4f6cib2c93848f5ec2661@mail.gmail.com>
Date:	Tue, 28 Jul 2009 14:49:38 -0700
From:	Martin Bligh <mbligh@...gle.com>
To:	Chad Talbott <ctalbott@...gle.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	wfg@...l.ustc.edu.cn, Michael Rubin <mrubin@...gle.com>,
	Andrew Morton <akpm@...gle.com>, sandeen@...hat.com
Subject: Re: Bug in kernel 2.6.31, Slow wb_kupdate writeout

> 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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