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    Subject[PATCH 4/4] capture pages freed during direct reclaim for allocation by the reclaimer
    When a process enters direct reclaim it will expend effort identifying
    and releasing pages in the hope of obtaining a page. However as these
    pages are released asynchronously there is every possibility that the
    pages will have been consumed by other allocators before the reclaimer
    gets a look in. This is particularly problematic where the reclaimer is
    attempting to allocate a higher order page. It is highly likely that
    a parallel allocation will consume lower order constituent pages as we
    release them preventing them coelescing into the higher order page the
    reclaimer desires.

    This patch set attempts to address this for allocations above
    ALLOC_COSTLY_ORDER by temporarily collecting the pages we are releasing
    onto a local free list. Instead of freeing them to the main buddy lists,
    pages are collected and coelesced on this per direct reclaimer free list.
    Pages which are freed by other processes are also considered, where they
    coelesce with a page already under capture they will be moved to the
    capture list. When pressure has been applied to a zone we then consult
    the capture list and if there is an appropriatly sized page available
    it is taken immediatly and the remainder returned to the free pool.
    Capture is only enabled when the reclaimer's allocation order exceeds
    ALLOC_COSTLY_ORDER as free pages below this order should naturally occur
    in large numbers following regular reclaim.

    Thanks go to Mel Gorman for numerous discussions during the development
    of this patch and for his repeated reviews.

    Signed-off-by: Andy Whitcroft <>

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      Last update: 2008-09-03 20:47    [W:0.020 / U:4.704 seconds]
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