Re: [PATCH 0/10] Reduce system disruption due to kswapd V2

[Zlatko Calusic]

On 12.04.2013 22:07, Zlatko Calusic wrote:
> On 12.04.2013 21:40, Mel Gorman wrote:
> > On Thu, Apr 11, 2013 at 10:55:13PM +0200, Zlatko Calusic wrote:
> > > On 09.04.2013 13:06, Mel Gorman wrote:
> > > <SNIP>
> > >
> > > - The only slightly negative thing I observed is that with the patch
> > > applied kswapd burns 10x - 20x more CPU. So instead of about 15
> > > seconds, it has now spent more than 4 minutes on one particular
> > > machine with a quite steady load (after about 12 days of uptime).
> > > Admittedly, that's still nothing too alarming, but...
> >
> > Would you happen to know what circumstances trigger the higher CPU
> > usage?
>
> Really nothing special. The server is lightly loaded, but it does enough
> reading from the disk so that pagecache is mostly populated and page
> reclaiming is active. So, kswapd is no doubt using CPU time gradually,
> nothing extraordinary.
>
> When I sent my reply yesterday, the server uptime was 12 days, and
> kswapd had accumulated 4:28 CPU time. Now, approx 24 hours later (13
> days uptime):
>
> root        23  0.0  0.0      0     0 ?        S    Mar30   4:52 [kswapd0]
>
> I will apply your v3 series soon and see if there's any improvement wrt
> CPU usage, although as I said I don't see that as a big issue. It's
> still only 0.013% of available CPU resources (dual core CPU).

JFTR, v3 kswapd uses about 15% more CPU time than v2. 2:50 kswapd CPU 
time after 6 days 14h uptime.

And find attached another debugging graph that shows how ANON pages are 
privileged in the ZONE_NORMAL on a 4GB machine. Take notice that the 
number of pages in the ZONE_DMA32 is scaled (/5) to fit the graph nicely.

--
Zlatko

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