linux-ext4 - Re: kernel thread "flush-254:12" eats 100% CPU

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Message-ID: <4E684F8C.3050308@tao.ma>
Date:	Thu, 08 Sep 2011 13:15:56 +0800
From:	Tao Ma <tm@....ma>
To:	Marcin M <gmane@...or.pl>
CC:	linux-ext4@...r.kernel.org
Subject: Re: kernel thread "flush-254:12" eats 100% CPU

On 09/07/2011 11:46 PM, Marcin M wrote:
> Hello!
> I hope i'm writing to correct place (but i suspect g.l.kernel list could
> be proper also) :)
> I'm observing situation like in subject. From time to time
> "flush-254:12" takes 100% of cpu for a couple of minutes. Then
> everything becomes ok.
> This problem appears on my two different boxes.
> 
> box A)
> bare metal, i686, hardened-kernel-2.6.{37-38}
> on this box kernel thread never stops to do 100% of cpu. I've to reboot
> box (using sysrq, because i could't even umount partition associated
> with this thread)
> My workarround for it: i changed ext4 to xfs on dm device and problem
> disappeared
So do you have the backstrace for it? Just wonder what it is doing.
echo t > /proc/sysrq-trigger should tell us what the flusher is doing at
that time.

Thanks
Tao
> 
> box B)
> xen, full virtualization, x86_64, kernels:
> hardened-kernel-{2.6.39,3.0.3,3.0.4} and 3.1.0-rc4-git2
> problem is as i described above, flush took one cpu for a couple minutes
> and then everythings works correctly.
> 
> And again, 254-12 device is ext4 filesystem.
> In both cases it was used lvm. At box B, additionaly i'm using dmcrypt.
> Box B is configured in this way: sda->lvm2->dmcrypt->filesystem.
> 
> How can i help to debug this problem? Or maybe it's fixed already?
> 
> Regards,
> Marcin.
> 
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