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SubjectRe: [PATCH] Add __GFP_MOVABLE for callers to flag allocations that may be migrated
On Mon, 4 Dec 2006, Mel Gorman wrote:

> 4. Offlining a DIMM
> 5. Offlining a Node
>
> For Situation 4, a zone may be needed because MAX_ORDER_NR_PAGES would have
> to be set to too high for anti-frag to be effective. However, zones would
> have to be tuned at boot-time and that would be an annoying restriction. If
> DIMMs are being offlined for power reasons, it would be sufficient to be
> best-effort.

We are able to depopularize a portion of the pages in a MAX_ORDER chunk if
the page structs pages on the borders of that portion are not stored on
the DIMM. Set a flag in the page struct of those page struct pages
straddling the border and free the page struct pages describing only
memory in the DIMM.

> Situation 5 requires that a hotpluggable node only allows __GFP_MOVABLE
> allocations in the zonelists. This would probably involving having one
> zone that only allowed __GFP_MOVABLE.

This is *node* hotplug and we already have a node/zone structure etc where
we could set some option to require only movable allocations. Note that
NUMA nodes have always had only a single effective zone. There are some
exceptions on some architectures where we have additional DMA zones on the
first or first two nodes but NUMA memory policies will *not* allow to
exercise control over allocations from those zones.

> In other words, to properly address all situations, we may need anti-frag
> and zones, not one or the other.

I still do not see a need for additional zones.
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