linux-kernel - Re: 3.12-rcX - NFS regression - kswapd0 / kswapd1 stays using 100% CPU?

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Date:	Thu, 31 Oct 2013 20:45:54 +0100
From:	Helge Deller <deller@....de>
To:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
CC:	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	NFS list <linux-nfs@...r.kernel.org>,
	linux-parisc <linux-parisc@...r.kernel.org>
Subject: Re: 3.12-rcX - NFS regression - kswapd0 / kswapd1 stays using 100%
 CPU?

On 10/19/2013 08:27 PM, Helge Deller wrote:
> On 10/18/2013 10:12 PM, Myklebust, Trond wrote:
>> On Fri, 2013-10-18 at 22:03 m, Helge Deller wrote:
>>> On 10/18/2013 09:36 PM, Myklebust, Trond wrote:
>>>> Also, could you please try a sysRQ-t the next time it happens, so that
>>>> we can get a trace of where the mount program is hanging. Knowing that
>>>> the mount is stuck in "__schedule()" is not really interesting unless we
>>>> know from where that was called.
>>>
>>> Actually, the machine was still running in this state.
>>> Here is sysrq-t:
>>> [112009.084000] mount           S 00000000401040c0     0 25331      1 0x00000010
>>> [112009.084000] Backtrace:
>>> [112009.084000]  [<0000000040113a68>] __schedule
>>> [112009.232000]
>>> [112009.232000] mount.nfs       D 00000000401040c0     0 25332  25331 0x00000010
>>> [112009.232000] Backtrace:
>>> [112009.232000]  [<0000000040113a68>] __schedule
>>
>> That makes no sense unless sysrq-t works differently on parisc than on
>> other platforms. I'd expect the backtrace to at least include a system
>> call. Parisc experts?
> 
> sysrq-t doesn't work differently on parisc. For other processes I do get
> a backtrace like the one on x86_64.
> That's the main reason why I asked for ideas here on the list.
> I do see the stuck process, but don't see any indications where it comes from.

I'm pretty sure that the regression (kswapd using 100% CPU) I reported here is fixed by this patch:
http://git.kernel.org/cgit/linux/kernel/git/deller/parisc-linux.git/commit/?id=c56b097af26cb11c1f49a4311ba538c825666fed

I will start some testing...

Helge
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