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    SubjectRe: [PATCH 0/4] Reclaim page capture v4
    On Wed,  1 Oct 2008 13:30:57 +0100
    Andy Whitcroft <> wrote:

    > For sometime we have been looking at mechanisms for improving the availability
    > of larger allocations under load. One of the options we have explored is
    > the capturing of pages freed under direct reclaim in order to increase the
    > chances of free pages coelescing before they are subject to reallocation
    > by racing allocators.
    > Following this email is a patch stack implementing page capture during
    > direct reclaim. It consits of four patches. The first two simply pull
    > out existing code into helpers for reuse. The third makes buddy's use
    > of struct page explicit. The fourth contains the meat of the changes,
    > and its leader contains a much fuller description of the feature.
    > This update represents a rebase to -mm and incorporates feedback from
    > KOSAKI Motohiro. It also incorporates an accounting fix which was
    > preventing some captures.
    > I have done a lot of comparitive testing with and without this patch
    > set and in broad brush I am seeing improvements in hugepage allocations
    > (worst case size) success on all of my test systems. These tests consist
    > of placing a constant stream of high order allocations on the system,
    > at varying rates. The results for these various runs are then averaged
    > to give an overall improvement.
    > Absolute Effective
    > x86-64 2.48% 4.58%
    > powerpc 5.55% 25.22%
    > x86-64 has a relatively small huge page size and so is always much more
    > effective at allocating huge pages. Even there we get a measurable
    > improvement. On powerpc the huge pages are much larger and much harder
    > to recover. Here we see a full 25% increase in page recovery.
    > It should be noted that these are worst case testing, and very agressive
    > taking every possible page in the system. It would be helpful to get
    > wider testing in -mm.
    > Against: 2.6.27-rc1-mm1
    > Andrew, please consider for -mm.

    Hmm, can't we use "MIGRATE_ISOLATE" pageblock type for this purpose ?
    The page allocater skips pageblock marked as MIGRATE_ISOLATE at allocation.
    (pageblock-size is equal to HUGEPAGE size in general.)

    Of course, "where should be isolated" is a problem.


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