Re: [patch] mm: fix deferred congestion timeout if preferred zone is not allowed

[David Rientjes <rientjes@google.com>]

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On Wed, 19 Jan 2011, Minchan Kim wrote:

> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -2034,6 +2034,18 @@ restart:
> >         */
> >        alloc_flags = gfp_to_alloc_flags(gfp_mask);
> >
> > +       /*
> > +        * If preferred_zone cannot be allocated from in this context, find the
> > +        * first allowable zone instead.
> > +        */
> > +       if ((alloc_flags & ALLOC_CPUSET) &&
> > +           !cpuset_zone_allowed_softwall(preferred_zone, gfp_mask)) {
> > +               first_zones_zonelist(zonelist, high_zoneidx,
> > +                               &cpuset_current_mems_allowed, &preferred_zone);
> 
> This patch is one we need. but I have a nitpick.
> I am not familiar with CPUSET so I might be wrong.
> 
> I think it could make side effect of statistics of ZVM on
> buffered_rmqueue since you intercept and change preferred_zone.
> It could make NUMA_HIT instead of NUMA_MISS.
> Is it your intention?
> 

It depends on the semantics of NUMA_MISS: if no local nodes are allowed by 
current's cpuset (a pretty poor cpuset config :), then it seems logical 
that all allocations would be a miss.