Re: [PATCH 07/27] mm, vmscan: Have kswapd only scan based on the highest requested zone

Johannes Weiner
2016-02-25T22:17:56Z

On Tue, Feb 23, 2016 at 03:04:30PM +0000, Mel Gorman wrote:
> kswapd checks all eligible zones to see if they need balancing even if it was
> woken for a lower zone. This made sense when we reclaimed on a per-zone basis
> because we wanted to shrink zones fairly so avoid age-inversion problems.
> Ideally this is completely unnecessary when reclaiming on a per-node basis.
> In theory, there may still be anomalies when all requests are for lower
> zones and very old pages are preserved in higher zones but this should be
> the exceptional case.
>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

As I mentioned in the other subthread, this should probably be fine,
although it would be good, generally, to have some sort of statistics
on how much of the age-distorting reclaim is happening, and then maybe
mention its existence in the changelog of this patch. Just an idea.