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    SubjectRe: [PATCH 6/8] mm: compaction: Perform a faster scan in try_to_compact_pages()
    On Wed, Nov 17, 2010 at 04:22:47PM +0000, Mel Gorman wrote:
    > @@ -485,8 +500,8 @@ static unsigned long compact_zone_order(struct zone *zone,
    > .nr_migratepages = 0,
    > .order = order,
    > .migratetype = allocflags_to_migratetype(gfp_mask),
    > + .migrate_fast_scan = true,
    > .zone = zone,
    > - .sync = false,
    > };
    > INIT_LIST_HEAD(&cc.freepages);
    > INIT_LIST_HEAD(&cc.migratepages);
    > @@ -502,8 +517,8 @@ unsigned long reclaimcompact_zone_order(struct zone *zone,
    > .nr_migratepages = 0,
    > .order = order,
    > .migratetype = allocflags_to_migratetype(gfp_mask),
    > + .migrate_fast_scan = false,
    > .zone = zone,
    > - .sync = true,
    > };

    Same as for the previous feature (sync/async migrate) I'd prefer if
    this was a __GFP_ flag (khugepaged will do the no-fast-scan version,
    page fault will only run compaction in fast scan mode) and if we
    removed the reclaimcompact_zone_order and we stick with the
    interleaving of shrinker and try_to_compact_pages from the alloc_pages
    caller, with no nesting of compaction inside the shrinker.

    Another possibility would be to not have those as __GFP flags, and to
    always do the first try_to_compact_pages with async+fast_scan, then
    call the shrinker and then all next try_to_compact_pages would be
    called with sync+no_fast_scan mode.

    But I love if we can further decrease the risk of too long page
    hugepage page fault before the normal page fallback, and to have a
    __GFP_ flag for these two. Even the same __GFP flag could work for

    So my preference would be to nuke reclaimcompact_zone_order, only
    stick to compact_zone_order and the current interleaving, and add a
    __GFP_COMPACT_FAST used by the hugepmd page fault (that will enable
    both async migrate and fast-scan). khugepaged and hugetlbfs won't use

    I'm undecided if a __GFP_ flag is needed to differentiate the callers,
    or if we should just run the first try_to_compact_pages in
    "optimistic" mode by default.

     \ /
      Last update: 2010-11-18 19:37    [W:0.041 / U:2.888 seconds]
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