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

[Mel Gorman]

On Wed, Apr 10, 2013 at 03:28:32PM -0700, dormando wrote:
> > On Tue, Apr 09, 2013 at 05:27:18PM +0000, Christoph Lameter wrote:
> > > One additional measure that may be useful is to make kswapd prefer one
> > > specific processor on a socket. Two benefits arise from that:
> > >
> > > 1. Better use of cpu caches and therefore higher speed, less
> > > serialization.
> > >
> >
> > Considering the volume of pages that kswapd can scan when it's active
> > I would expect that it trashes its cache anyway. The L1 cache would be
> > flushed after scanning struct pages for just a few MB of memory.
> >
> > > 2. Reduction of the disturbances to one processor.
> > >
> >
> > I've never checked it but I would have expected kswapd to stay on the
> > same processor for significant periods of time. Have you experienced
> > problems where kswapd bounces around on CPUs within a node causing
> > workload disruption?
> 
> When kswapd shares the same CPU as our main process it causes a measurable
> drop in response time (graphs show tiny spikes at the same time memory is
> freed). Would be nice to be able to ensure it runs on a different core
> than our latency sensitive processes at least. We can pin processes to
> subsets of cores but I don't think there's a way to keep kswapd from
> waking up on any of them?

I've never tried it myself but does the following work?

taskset -p MASK `pidof kswapd`

where MASK is a cpumask describing what CPUs kswapd can run on?
Obviously care should be taken to ensure that you bind kswapd to a CPU
running on the node kswapd cares about.

-- 
Mel Gorman
SUSE Labs
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