linux-kernel - Re: kswapd craziness round 2

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Date:	Mon, 18 Feb 2013 23:05:56 +0800
From:	Daniel J Blueman <daniel@...ascale-asia.com>
To:	Hillf Danton <dhillf@...il.com>
CC:	Jiri Slaby <jslaby@...e.cz>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Steffen Persvold <sp@...ascale.com>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: kswapd craziness round 2

On 18/02/2013 19:42, Hillf Danton wrote:
> On Mon, Feb 18, 2013 at 2:18 PM, Daniel J Blueman
> <daniel@...ascale-asia.com> wrote:
>> On Monday, 18 February 2013 06:10:02 UTC+8, Jiri Slaby  wrote:
>>
>>> Hi,
>>>
>>> You still feel the sour taste of the "kswapd craziness in v3.7" thread,
>>> right? Welcome to the hell, part two :{.
>>>
>>> I believe this started happening after update from
>>> 3.8.0-rc4-next-20130125 to 3.8.0-rc7-next-20130211. The same as before,
>>> many hours of uptime are needed and perhaps some suspend/resume cycles
>>> too. Memory pressure is not high, plenty of I/O cache:
>>> # free
>>>               total       used       free     shared    buffers     cached
>>> Mem:       6026692    5571184     455508          0     351252    2016648
>>> -/+ buffers/cache:    3203284    2823408
>>> Swap:            0          0          0
>>>
>>> kswap is working very toughly though:
>>> root       580  0.6  0.0      0     0 ?        S    úno12  46:21 [kswapd0]
>>>
>>> This happens on I/O activity right now. For example by updatedb or find
>>> /. This is what the stack trace of kswapd0 looks like:
>>> [<ffffffff8113c431>] shrink_slab+0xa1/0x2d0
>>> [<ffffffff8113ecd1>] kswapd+0x541/0x930
>>> [<ffffffff810a3000>] kthread+0xc0/0xd0
>>> [<ffffffff816beb5c>] ret_from_fork+0x7c/0xb0
>>> [<ffffffffffffffff>] 0xffffffffffffffff
>>
>> Likewise with 3.8-rc, I've been able to reproduce [1] a livelock scenario
>> which hoses the box and observe RCU stalls [2].
>>
>> There may be a connection; I'll do a bit more debugging in the next few
>> days.
>>
>> Daniel
>>
>> --- [1]
>>
>> 1. live-booted image using ramdisk
>> 2. boot 3.8-rc with <16GB memory and without swap
>> 3. run OpenMP NAS Parallel Benchmark dc.B against local disk (ie not
>> ramdisk)
>> 4. observe hang O(30) mins later
>>
>> --- [2]
>>
>> [ 2675.587878] INFO: rcu_sched self-detected stall on CPU { 5}  (t=24000
>> jiffies g=6313 c=6312 q=68)
>
> Does Ingo's revert help? https://lkml.org/lkml/2013/2/15/168

Close, but no cigar; I still hit this livelock on 3.8-rc7 with Ingo's 
revert or Linus's fix.

However, I am unable to reproduce the hang with 3.7.9, so will begin 
bisection tomorrow, probably automating via pexpect.

Thanks,
   Daniel
-- 
Daniel J Blueman
Principal Software Engineer, Numascale Asia
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