Re: [PATCH] mm: wait for congestion to clear on all zones

[Zlatko Calusic]

On 09.01.2013 22:48, Andrew Morton wrote:
> On Wed, 09 Jan 2013 22:41:48 +0100
> Zlatko Calusic <zlatko.calusic@xxxxxxxx> wrote:
>
> > Currently we take a short nap (HZ/10) and wait for congestion to clear
> > before taking another pass with lower priority in balance_pgdat(). But
> > we do that only for the highest zone that we encounter is unbalanced
> > and congested.
> >
> > This patch changes that to wait on all congested zones in a single
> > pass in the hope that it will save us some scanning that way. Also we
> > take a nap as soon as congested zone is encountered and sc.priority <
> > DEF_PRIORITY - 2 (aka kswapd in trouble).
> >
> > ...
> >
> > The patch is against the mm tree. Make sure that
> > mm-avoid-calling-pgdat_balanced-needlessly.patch is applied first (not
> > yet in the mmotm tree). Tested on half a dozen systems with different
> > workloads for the last few days, working really well!
>
> But what are the user-observable effcets of this change?  Less kernel
> CPU consumption, presumably?  Did you quantify it?

And I forgot to answer all the questions... :(

Actually, I did record kswapd CPU usage after 5 days of uptime and I 
intend to compare it with the new data (after few more days pass). I 
expect maybe slightly better results.

But, I think it's obvious from my first reply that my primary goal with 
this patch is correctness, not optimization. So, I won't be dissapointed 
a little bit if kswapd CPU usage stays the same, so long as the memory 
utilization remains this smooth. ;)

--
Zlatko
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