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@xxxxxxxxxx> > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> > Acked-by: Mel Gorman <mgorman@xxxxxxx> > Acked-by: Rik van Riel <riel@xxxxxxxxxx> > Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx> > --- > 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>