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    SubjectRe: [PATCH 05/11] mm: compaction: Determine if dirty pages can be migrated without blocking within ->migratepage
    On 12/14/2011 10:41 AM, Mel Gorman wrote:
    > Asynchronous compaction is used when allocating transparent hugepages
    > to avoid blocking for long periods of time. Due to reports of
    > stalling, there was a debate on disabling synchronous compaction
    > but this severely impacted allocation success rates. Part of the
    > reason was that many dirty pages are skipped in asynchronous compaction
    > by the following check;
    >
    > if (PageDirty(page)&& !sync&&
    > mapping->a_ops->migratepage != migrate_page)
    > rc = -EBUSY;
    >
    > This skips over all mapping aops using buffer_migrate_page()
    > even though it is possible to migrate some of these pages without
    > blocking. This patch updates the ->migratepage callback with a "sync"
    > parameter. It is the responsibility of the callback to fail gracefully
    > if migration would block.
    >
    > Signed-off-by: Mel Gorman<mgorman@suse.de>

    Reviewed-by: Rik van Riel <riel@redhat.com>

    --
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