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    SubjectRe: [PATCH v3 04/10] compaction: make isolate_lru_page with filter aware
    On Tue, Jun 07, 2011 at 11:38:17PM +0900, Minchan Kim wrote:
    > In async mode, compaction doesn't migrate dirty or writeback pages.
    > So, it's meaningless to pick the page and re-add it to lru list.
    >
    > Of course, when we isolate the page in compaction, the page might
    > be dirty or writeback but when we try to migrate the page, the page
    > would be not dirty, writeback. So it could be migrated. But it's
    > very unlikely as isolate and migration cycle is much faster than
    > writeout.
    >
    > So, this patch helps cpu and prevent unnecessary LRU churning.
    >
    > Cc: Andrea Arcangeli <aarcange@redhat.com>
    > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    > Acked-by: Johannes Weiner <hannes@cmpxchg.org>
    > Acked-by: Mel Gorman <mgorman@suse.de>
    > Acked-by: Rik van Riel <riel@redhat.com>
    > Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
    > ---
    > mm/compaction.c | 7 +++++--
    > 1 files changed, 5 insertions(+), 2 deletions(-)
    >
    > diff --git a/mm/compaction.c b/mm/compaction.c
    > index f0d75e9..8079346 100644
    > --- a/mm/compaction.c
    > +++ b/mm/compaction.c
    > @@ -243,6 +243,7 @@ static unsigned long isolate_migratepages(struct zone *zone,
    > unsigned long last_pageblock_nr = 0, pageblock_nr;
    > unsigned long nr_scanned = 0, nr_isolated = 0;
    > struct list_head *migratelist = &cc->migratepages;
    > + enum ISOLATE_MODE mode = ISOLATE_ACTIVE|ISOLATE_INACTIVE;
    >
    > /* Do not scan outside zone boundaries */
    > low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
    > @@ -326,9 +327,11 @@ static unsigned long isolate_migratepages(struct zone *zone,
    > continue;
    > }
    >
    > + if (!cc->sync)
    > + mode |= ISOLATE_CLEAN;
    > +
    > /* Try isolate the page */
    > - if (__isolate_lru_page(page,
    > - ISOLATE_ACTIVE|ISOLATE_INACTIVE, 0) != 0)
    > + if (__isolate_lru_page(page, mode, 0) != 0)
    > continue;
    >
    > VM_BUG_ON(PageTransCompound(page));

    Looks good for compaction! This change makes a lot of sense.

    However I would expand the meaning of this patch. Introduce
    ISOLATE_CLEAN in this patch and update both compaction and
    __zone_reclaim. You might encounter some mess mapping RECLAIM_WRITE to
    ISOLATE_CLEAN but nothing unmanageable.

    --
    Mel Gorman
    SUSE Labs


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