Re: kswapd continuously active

From: Jens Axboe
Date: Fri Feb 05 2010 - 08:12:26 EST


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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/