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SubjectRe: [PATCH 1/11] Add __GFP_MOVABLE flag and update callers
On Fri, 24 Nov 2006, Christoph Lameter wrote:

> On Thu, 23 Nov 2006, Linus Torvalds wrote:
>
>> And the assumption would be that if it's MOVABLE, then it's obviously a
>> USER allocation (it it can fail much more eagerly - that's really what the
>> whole USER bit ends up meaning internally).
>
> We can probably make several types of kernel allocations movable if there
> would be some benefit from it.
>

Page tables are the major type of allocation that comes to mind. From what
I've seen, they are the most common long-lived unmovable and unreclaimable
allocation.

> Mel already has a problem with mlocked user pages in the movable section.
> If this is fixed by using page migration to move the mlocked pages

That is the long-term plan.

> then we
> can likely make addititional classes kernel pages also movable and reduce
> the amount of memory that is unmovable. If we have more movable pages then
> the defrag can work more efficiently.

Indeed, although some sort of placement is still needed to keep these
movable allocations together.

> Having most pages movable will also
> help to make memory unplug a reality.
>
> So please do not require movable pages to be user allocations.
>

That is not the intention. It just happens that allocations that are
directly accessible by userspace are also the ones that are currently
movable.

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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