Re: [PATCH] vmscan: fix zone balance check in prepare_kswapd_sleep

[Mel Gorman <mgorman@techsingularity.net>]

On Mon, Feb 06, 2017 at 07:16:46PM -0500, Shantanu Goel wrote:
> > However, note that there is a slight risk that kswapd will sleep for a
> > short interval early due to a very small zone such as ZONE_DMA. If this
> > is a general problem then it'll manifest as less kswapd reclaim and more
> > direct reclaim. If it turns out this is an issue then a revert will not
> > be the right fix. Instead, all the checks for zone_balance will need to
> > account for the only balanced zone being a tiny percentage of memory in
> > the node.
> > 
> 
> I see your point.  Perhaps we can introduce a constraint that
> ensures the balanced zones constitute say 1/4 or 1/2 of
> memory in the classzone?  I believe there used to be such
> a constraint at one time for higher order allocations.
> 

There was but it was fairly complex and I'd rather avoid it if at all
possible and certainly not without data backing it up.

-- 
Mel Gorman
SUSE Labs

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