On Fri, Jun 24, 2016 at 11:54:33AM +0200, Vlastimil Babka wrote: > The __compact_finished() function uses low watermark in a check that has to > pass if the direct compaction is to finish and allocation should succeed. This > is too pessimistic, as the allocation will typically use min watermark. It may > happen that during compaction, we drop below the low watermark (due to parallel > activity), but still form the target high-order page. By checking against low > watermark, we might needlessly continue compaction. > > Similarly, __compaction_suitable() uses low watermark in a check whether > allocation can succeed without compaction. Again, this is unnecessarily > pessimistic. > > After this patch, these check will use direct compactor's alloc_flags to > determine the watermark, which is effectively the min watermark. > > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> > Acked-by: Michal Hocko <mhocko@xxxxxxxx> > --- > mm/compaction.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 76897850c3c2..371760a85085 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1320,7 +1320,7 @@ static enum compact_result __compact_finished(struct zone *zone, struct compact_ > return COMPACT_CONTINUE; > > /* Compaction run is not finished if the watermark is not met */ > - watermark = low_wmark_pages(zone); > + watermark = zone->watermark[cc->alloc_flags & ALLOC_WMARK_MASK]; finish condition is changed. We have two more watermark checks in try_to_compact_pages() and kcompactd_do_work() and they should be changed too. Thanks. > > if (!zone_watermark_ok(zone, cc->order, watermark, cc->classzone_idx, > cc->alloc_flags)) > @@ -1385,7 +1385,7 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order, > if (is_via_compact_memory(order)) > return COMPACT_CONTINUE; > > - watermark = low_wmark_pages(zone); > + watermark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK]; > /* > * If watermarks for high-order allocation are already met, there > * should be no need for compaction at all. > @@ -1399,7 +1399,7 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order, > * This is because during migration, copies of pages need to be > * allocated and for a short time, the footprint is higher > */ > - watermark += (2UL << order); > + watermark = low_wmark_pages(zone) + (2UL << order); > if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx, > alloc_flags, wmark_target)) > return COMPACT_SKIPPED; > -- > 2.8.4 -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>