linux-kernel - Re: khugepaged: gets stuck when writing to USB flash, 2.6.38-rc2

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Date:	Tue, 1 Feb 2011 22:24:00 +0100
From:	Jindřich Makovička <makovick@...il.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: khugepaged: gets stuck when writing to USB flash, 2.6.38-rc2

2011/2/1 Andrea Arcangeli <aarcange@...hat.com>:
>> When copying 4GB or more in one go from HDD to Flash, during the
>> copying, fork() and probably other syscalls involving VM start
>> blocking (I first observed the problem in Chrome, which refused to
>> display content in new tabs). When one lets the copying finish, the
>> system returns to a usable state.
>>
>> During the limbo, khugepaged is in D state (uninterruptible sleep).
>
> That means no hugepage could be allocated. Maybe memory compaction is
> doing an overwork because all pagecache is dirty and can't be
> migrated. This should solve it if it's memory compaction:
>
> echo never >/sys/kernel/mm/transparent_hugepage/defrag
>
> kswapd state would be interesting too. Can you sysrq+t?

With -rc2, there is

$ ps aux | grep -E "kswap|khugep"
root       474  0.0  0.0      0     0 ?        S    20:44   0:00 [kswapd0]
root       540  0.0  0.0      0     0 ?        DN   20:44   0:00 [khugepaged]

Sysrq-t output is attached.

Good news is, I don't see these issues with -rc3.

Regards,
-- 
Jindrich Makovicka

Download attachment "sysrq-t.txt.gz" of type "application/x-gzip" (14135 bytes)