On Fri, Jan 06, 2012 at 10:50:01AM +0800, Huang Shijie wrote: > We get cc->order is -1 when user echos to /proc/sys/vm/compact_memory. > In this case, we should check that if we have enough pages for > the compaction in the zone. > > If we do not check this, in our MX6Q board(arm), i ever observed > COMPACT_CLUSTER_MAX pages were compaction failed in per migrate_pages(). > Thats mean we can not alloc any pages by the free scanner in the zone. > It seems this patch is useful but I can't parse your this sentense. Could you elaborate on it? We should know about exactly why order == -1 is COMPACT_CLUSTER_MAX * 2 and other case 2UL << order. If you write down description more clear, it will help. Thanks. > This patch checks the watermark to avoid this problem. > Tested this patch in the MX6Q board. > > Signed-off-by: Huang Shijie <b32955@xxxxxxxxxxxxx> > --- > mm/compaction.c | 18 +++++++++--------- > 1 files changed, 9 insertions(+), 9 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 899d956..bf8e8b2 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -479,21 +479,21 @@ unsigned long compaction_suitable(struct zone *zone, int order) > unsigned long watermark; > > /* > + * Watermarks for order-0 must be met for compaction. > + * During the migration, copies of pages need to be > + * allocated and for a short time, so the footprint is higher. > * order == -1 is expected when compacting via > - * /proc/sys/vm/compact_memory > + * /proc/sys/vm/compact_memory. > */ > - if (order == -1) > - return COMPACT_CONTINUE; > + watermark = low_wmark_pages(zone) + > + ((order == -1) ? (COMPACT_CLUSTER_MAX * 2) : (2UL << order)); > > - /* > - * Watermarks for order-0 must be met for compaction. Note the 2UL. > - * This is because during migration, copies of pages need to be > - * allocated and for a short time, the footprint is higher > - */ > - watermark = low_wmark_pages(zone) + (2UL << order); > if (!zone_watermark_ok(zone, 0, watermark, 0, 0)) > return COMPACT_SKIPPED; > > + if (order == -1) > + return COMPACT_CONTINUE; > + > /* > * fragmentation index determines if allocation failures are due to > * low memory or external fragmentation > -- > 1.7.3.2 > > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. 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> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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>