Re: [PATCH 5/6] mm: page_alloc: Abort fair zone allocation policy when remotes nodes are encountered

From: Mel Gorman
Date: Thu Jul 10 2014 - 08:44:16 EST

On Thu, Jul 10, 2014 at 08:14:19AM -0400, Johannes Weiner wrote:
> On Wed, Jul 09, 2014 at 09:13:07AM +0100, Mel Gorman wrote:
> > The purpose of numa_zonelist_order=zone is to preserve lower zones
> > for use with 32-bit devices. If locality is preferred then the
> > numa_zonelist_order=node policy should be used. Unfortunately, the fair
> > zone allocation policy overrides this by skipping zones on remote nodes
> > until the lower one is found. While this makes sense from a page aging
> > and performance perspective, it breaks the expected zonelist policy. This
> > patch restores the expected behaviour for zone-list ordering.
> >
> > Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> 32-bit NUMA? :-)

I'm tempted to just say "it can go on fire" but realistically speaking
they should be configured to use node ordering. I was very tempted to
always force node ordering but I didn't have good data on how often lowmem
allocations are required on NUMA machines.

> Anyway, this change also cuts down the fair pass
> overhead on bigger NUMA machines, so I'm all for it.
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Thanks for the reviews!

Mel Gorman
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