linux-kernel - Re: slow performance on disk/network i/o full speed after drop

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Message-ID: <CAC8teKXqZktBK7+GbLgHn-2k+zjjf8uieRM_q_V7JK7ePAk9Lg@mail.gmail.com>
Date:	Fri, 26 Aug 2011 11:30:35 +0800
From:	Zhu Yanhai <zhu.yanhai@...il.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Stefan Priebe <s.priebe@...fihost.ag>,
	Pekka Enberg <penberg@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, Jens Axboe <jaxboe@...ionio.com>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: slow performance on disk/network i/o full speed after drop_caches

Fengguang,
Maybe it's because zone_reclaim_mode? We often have received some reports that
scp or something like that is slow with no reason, and mostly it's due
to someone
enabled zone_reclaim_mode by mistake.

Stefan, is your zone_reclaim_mode enabled? try 'cat
/proc/sys/vm/zone_reclaim_mode',
and echo 0 to it to disable.

Thanks,
Zhu Yanhai

2011/8/26 Wu Fengguang <fengguang.wu@...el.com>:
> On Fri, Aug 26, 2011 at 11:13:07AM +0800, Stefan Priebe wrote:
>>
>> >> There is at least a numastat proc file.
>> >
>> > Thanks. This shows that node0 is accessed 10x more than node1.
>>
>> What can i do to prevent this or isn't this normal when a machine mostly idles so processes are mostly processed by cpu0.
>
> Yes, that's normal. However it should explain why it's slow even when
> there are lots of free pages _globally_.
>
>> >
>> >> complete ps output:
>> >> http://pastebin.com/raw.php?i=b948svzN
>> >
>> > In that log, scp happens to be in R state and also no other tasks in D
>> > state. Would you retry in the hope of catching some stucked state?
>> Sadly not as the sysrq trigger has rebootet the machine and it will now run fine for 1 or 2 days.
>
> Oops, sorry! It might be possible to reproduce the issue by manually
> eating all of the memory with sparse file data:
>
>        truncate -s 1T 1T
>        cp 1T /dev/null
>
>> >
>> >>>         echo t>  /proc/sysrq-trigger
>> >> sadly i wa sonly able to grab the output in this crazy format:
>> >> http://pastebin.com/raw.php?i=MBXvvyH1
>> >
>> > It's pretty readable dmesg, except that the data is incomplete and
>> > there are nothing valuable in the uploaded portion..
>> That was everything i could grab through netconsole. Is there a better way?
>
> netconsole is enough.  The partial output should be due to the reboot...
>
> Thanks,
> Fengguang
>
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