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    SubjectRe: [PATCH 3/3] compaction accouting fix
    On Sun, Nov 13, 2011 at 01:37:43AM +0900, Minchan Kim wrote:
    > I saw the following accouting of compaction during test of the series.
    >
    > compact_blocks_moved 251
    > compact_pages_moved 44
    >
    > It's very awkward to me although it's possbile because it means we try to compact 251 blocks
    > but it just migrated 44 pages. As further investigation, I found isolate_migratepages doesn't
    > isolate any pages but it returns ISOLATE_SUCCESS and then, it just increases compact_blocks_moved
    > but doesn't increased compact_pages_moved.
    >
    > This patch makes accouting of compaction works only in case of success of isolation.
    >
    > CC: Mel Gorman <mgorman@suse.de>
    > CC: Johannes Weiner <jweiner@redhat.com>
    > CC: Rik van Riel <riel@redhat.com>
    > Signed-off-by: Minchan Kim <minchan.kim@gmail.com>

    Acked-by: Johannes Weiner <jweiner@redhat.com>

    It's a teensy-bit awkward that isolate_migratepages() can return
    success without actually isolating any new pages, just because there
    are still some pages left from a previous run (cc->nr_migratepages is
    maintained across isolation calls).

    Maybe isolate_migratepages() should just return an error if compaction
    should really be aborted and 0 otherwise, and have compact_zone()
    always check for cc->nr_migratepages itself?

    if (isolate_migratepages(zone, cc) < 0) {
    ret = COMPACT_PARTIAL;
    goto out;
    }

    if (!cc->nr_migratepages)
    continue;

    ...

    Just a nit-pick, though. If you don't agree, just leave it as is.


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