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    Subject[PATCH 16/34] mm: compaction: Allow compaction to isolate dirty pages
    Date
    commit a77ebd333cd810d7b680d544be88c875131c2bd3 upstream.

    Stable note: Not tracked in Bugzilla. A fix aimed at preserving page aging
    information by reducing LRU list churning had the side-effect of
    reducing THP allocation success rates. This was part of a series
    to restore the success rates while preserving the reclaim fix.

    Commit [39deaf85: mm: compaction: make isolate_lru_page() filter-aware]
    noted that compaction does not migrate dirty or writeback pages and
    that is was meaningless to pick the page and re-add it to the LRU list.

    What was missed during review is that asynchronous migration moves
    dirty pages if their ->migratepage callback is migrate_page() because
    these can be moved without blocking. This potentially impacted
    hugepage allocation success rates by a factor depending on how many
    dirty pages are in the system.

    This patch partially reverts 39deaf85 to allow migration to isolate
    dirty pages again. This increases how much compaction disrupts the
    LRU but that is addressed later in the series.

    Signed-off-by: Mel Gorman <mgorman@suse.de>
    Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
    Reviewed-by: Rik van Riel <riel@redhat.com>
    Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
    ---
    mm/compaction.c | 3 ---
    1 file changed, 3 deletions(-)

    diff --git a/mm/compaction.c b/mm/compaction.c
    index 61e68a5..afdc416 100644
    --- a/mm/compaction.c
    +++ b/mm/compaction.c
    @@ -371,9 +371,6 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
    continue;
    }

    - if (!cc->sync)
    - mode |= ISOLATE_CLEAN;
    -
    /* Try isolate the page */
    if (__isolate_lru_page(page, mode, 0) != 0)
    continue;
    --
    1.7.9.2


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