Re: NUMA policy issues with ZONE_MOVABLE

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

On Wed, 2007-07-25 at 12:16 +0100, Mel Gorman wrote:
> On (24/07/07 21:20), Christoph Lameter didst pronounce:
> > The outcome of the 2.6.23 merge was surprising. No antifrag but only 
> > ZONE_MOVABLE. ZONE_MOVABLE is the highest zone.
> > 
> > For the NUMA layer this has some weird consequences if ZONE_MOVABLE is populated
> > 
> > 1. It is the highest zone.
> > 
> > 2. Thus policy_zone == ZONE_MOVABLE
> > 
> > ZONE_MOVABLE contains only movable allocs by default. That is anonymous 
> > pages and page cache pages?
> > 
> > The NUMA layer only supports NUMA policies for the highest zone. 
> > Thus NUMA policies can control anonymous pages and the page cache pages 
> > allocated from ZONE_MOVABLE. 
> > 
> > However, NUMA policies will no longer affect non pagecache and non 
> > anonymous allocations. So policies can no longer redirect slab allocations 
> > and huge page allocations (unless huge page allocations are moved to 
> > ZONE_MOVABLE). And there are likely other allocations that are not 
> > movable.
> > 
> > If ZONE_MOVABLE is off then things should be working as normal.
> > 
> > Doesnt this mean that ZONE_MOVABLE is incompatible with CONFIG_NUMA?
> >  
> 
> No but it has to be dealt with. I would have preferred this was highlighted
> earlier but there is a candidate fix below.  It appears to be the minimum
> solution to allow policies to work as they do today but remaining compatible
> with ZONE_MOVABLE. It works by
> 
> o check_highest_zone will be the highest populated zone that is not ZONE_MOVEABLE

Ah, sick minds think alike...  ;-)

Lee

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