linux-ext4 - Re: Excessive stall times on ext4 in 3.9-rc2

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Message-ID: <515AF348.7060209@gmail.com>
Date:	Tue, 02 Apr 2013 23:03:36 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	linux-ext4@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>, Jiri Slaby <jslaby@...e.cz>
Subject: Re: Excessive stall times on ext4 in 3.9-rc2

Hi Mel,

Thanks for reporting it.

On 04/02/2013 10:27 PM, Mel Gorman wrote:
> I'm testing a page-reclaim-related series on my laptop that is partially
> aimed at fixing long stalls when doing metadata-intensive operations on
> low memory such as a git checkout. I've been running 3.9-rc2 with the
> series applied but found that the interactive performance was awful even
> when there was plenty of free memory.
> 
> I activated a monitor from mmtests that logs when a process is stuck for
> a long time in D state and found that there are a lot of stalls in ext4.
> The report first states that processes have been stalled for a total of
> 6498 seconds on IO which seems like a lot. Here is a breakdown of the
> recorded events.

In this merge window, we add a status tree as a extent cache.  Meanwhile
a es_cache shrinker is registered to try to reclaim from this cache when
we are under a high memory pressure.  So I suspect that the root cause
is this shrinker.  Could you please tell me how to reproduce this
problem?  If I understand correctly, I can run mmtest to reproduce this
problem, right?

Thanks,
						- Zheng
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