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    SubjectRe: [PATCH 0/3] Removal of lumpy reclaim V2
    On 04/11/2012 12:38 PM, Mel Gorman wrote:

    > Success rates are completely hosed for 3.4-rc2 which is almost certainly
    > due to [fe2c2a10: vmscan: reclaim at order 0 when compaction is enabled]. I
    > expected this would happen for kswapd and impair allocation success rates
    > (https://lkml.org/lkml/2012/1/25/166) but I did not anticipate this much
    > a difference: 80% less scanning, 37% less reclaim by kswapd

    Also, no gratuitous pageouts of anonymous memory.
    That was what really made a difference on a somewhat
    heavily loaded desktop + kvm workload.

    > In comparison, reclaim/compaction is not aggressive and gives up easily
    > which is the intended behaviour. hugetlbfs uses __GFP_REPEAT and would be
    > much more aggressive about reclaim/compaction than THP allocations are. The
    > stress test above is allocating like neither THP or hugetlbfs but is much
    > closer to THP.

    Next step: get rid of __GFP_NO_KSWAPD for THP, first
    in the -mm kernel

    > Mainline is now impaired in terms of high order allocation under heavy load
    > although I do not know to what degree as I did not test with __GFP_REPEAT.
    > Keep this in mind for bugs related to hugepage pool resizing, THP allocation
    > and high order atomic allocation failures from network devices.

    This might be due to smaller allocations not bumping
    the compaction deferring code, when we have deferred
    compaction for a higher order allocation.

    I wonder if the compaction deferring code is simply
    too defer-happy, now that we ignore compaction at
    lower orders than where compaction failed?


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