Lumpy Reclaim V3

Some weeks back I posted a linear reclaim patch series. Discussions on that led Peter Zijlstra to propose new simpler block based reclaim algorithm called 'lumpy'. We have been testing variants of this to try and improve its effectivness to close to that of the heavier weight linear algorithm. The stack below both remains simple but gives us pretty useful reclaim rates.

I have left the changes broken out for the time being so as to make it clear what is the original and what is my fault. I would expect to roll this up before acceptance.

-apw

=== 8< ===
Lumpy Reclaim (V3)

When we are out of memory of a suitable size we enter reclaim. The current reclaim algorithm targets pages in LRU order, which is great for fairness but highly unsuitable if you desire pages at higher orders. To get pages of higher order we must shoot down a very high proportion of memory; >95% in a lot of cases.

This patch set adds a lumpy reclaim algorithm to the allocator. It targets groups of pages at the specified order anchored at the end of the active and inactive lists. This encourages groups of pages at the requested orders to move from active to inactive, and active to free lists. This behaviour is only triggered out of direct reclaim when higher order pages have been requested.

This patch set is particularly effective when utilised with an anti-fragmentation scheme which groups pages of similar reclaimability together.

This patch set (against 2.6.19-rc5-mm2) is based on Peter Zijlstra's lumpy reclaim V2 patch which forms the foundation. It comprises the following patches:

lumpy-reclaim-v2 -- Peter Zijlstra's lumpy reclaim prototype,

lumpy-cleanup-a-missplaced-comment-and-simplify-some-code --
cleanups to move a comment back to where it came from, to make the area edge selection more comprehensible and also cleans up the switch coding style to match the concensus in mm/*.c,

lumpy-ensure-we-respect-zone-boundaries -- bug fix to ensure we do
not attempt to take pages from adjacent zones, and

lumpy-take-the-other-active-inactive-pages-in-the-area -- patch to
increase aggression over the targetted order.

Testing of this patch set under high fragmentation high allocation load conditions shows significantly improved high order reclaim rates than a standard kernel. The stack here it is now within 5% of the best case linear-reclaim figures.

It would be interesting to see if this setup is also successful in reducing order-2 allocation failures that you have been seeing with jumbo frames.

Please consider for -mm.

-apw

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