Re: [PATCH 1/11] Add __GFP_MOVABLE flag and update callers

From: Mel Gorman
Date: Fri Nov 24 2006 - 15:05:27 EST

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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