linux-kernel - Re: kswapd continuously active

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Message-ID: <20100205131220.GK1025@kernel.dk>
Date:	Fri, 5 Feb 2010 14:12:21 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Jan Engelhardt <jengelh@...ozas.de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: kswapd continuously active

On Fri, Feb 05 2010, Jan Engelhardt wrote:
> 
> On Friday 2010-02-05 14:00, Jens Axboe wrote:
> >> >January 25			Feb-05
> >> >MemTotal:        8166752 kB	8166752
> >> >MemFree:         3243552 kB	3781776
> >> >Buffers:          207968 kB	4912
> >> >Cached:          2728216 kB	2684400
> >> >SwapCached:            0 kB	0
> >> >Active:          2203136 kB	495624
> >> >Inactive:        2152544 kB	3263136
> >> >Active(anon):    1167256 kB	488168
> >> >Inactive(anon):   252952 kB	583912
> >> >Active(file):    1035880 kB	7456
> >> >Inactive(file):  1899592 kB	2679224
> >> >Unevictable:           0 kB	0
> >> >Mlocked:               0 kB	0
> >> >SwapTotal:             0 kB	0
> >> >SwapFree:              0 kB	0
> >> >Dirty:            141624 kB	2662184
> >> >Writeback:             0 kB	..
> >> 
> >> Today this happened again. So I looked at /proc/meminfo to paste today's
> >> values next to those from January. That is when I noticed the "Dirty"
> >> value - and thus I ran
> >> 
> >> 	watch -d -n 1 'grep Dirty /proc/meminfo'
> >> 
> >> What I see is that the dirty amount - a sync is currently running -
> >> only decreases with at most 400 KB/sec, often less than that.
> >
> >I'm guessing the barriers and commits are what is killing your
> >performance. What happens with barrier=0?
> 
> The ext4 filesystem is already mounted with barrier=0. If there
> is any block-level barriers I also can turn off, what would be
> the command?

barrier=0 is enough. I do wonder why your writeback rate is that slow,
then. The disk has write back caching enabled?

-- 
Jens Axboe

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