When I tested compaction in low memory condition, I found that my benchmark is stuck in congestion_wait() at shrink_inactive_list(). This stuck last for 1 sec and after then it can escape. More investigation shows that it is due to stale vmstat value. vmstat is updated every 1 sec so it is stuck for 1 sec. I guess that it is caused by updating NR_ISOLATED_XXX. In direct reclaim/compaction, it would isolate some pages. After some processing, they are returned to lru or freed and NR_ISOLATED_XXX is adjusted so it should be recover to zero. But, it would be possible that some updatings are appiled to global but some are applied only to per cpu variable. In this case, zone_page_state() would return stale value so it can be stuck. This problem can be solved by adjusting zone_page_state() with this cpu's vmstat value. It's sub-optimal because the other task in other cpu can be stuck due to stale vmstat value but, at least, it can solve some usecases without adding much overhead so I think that it is worth to doing it. With this change, I can't find any stuck in my test. Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> --- include/linux/vmstat.h | 3 +++ 1 file changed, 3 insertions(+) diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h index 62af0f8..7c84896 100644 --- a/include/linux/vmstat.h +++ b/include/linux/vmstat.h @@ -133,6 +133,9 @@ static inline unsigned long zone_page_state(struct zone *zone, { long x = atomic_long_read(&zone->vm_stat[item]); #ifdef CONFIG_SMP + long diff = this_cpu_read(zone->pageset->vm_stat_diff[item]); + + x += diff; if (x < 0) x = 0; #endif -- 1.9.1 -- 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>