On Wed, 15 Sep 2010 13:27:51 +0100 Mel Gorman <mel@xxxxxxxxx> wrote: > If wait_iff_congested() is called with no BDI congested, the function simply > calls cond_resched(). In the event there is significant writeback happening > in the zone that is being reclaimed, this can be a poor decision as reclaim > would succeed once writeback was completed. Without any backoff logic, > younger clean pages can be reclaimed resulting in more reclaim overall and > poor performance. This is because cond_resched() is a no-op, and we skip around the under-writeback pages and go off and look further along the LRU for younger clean pages, yes? > This patch tracks how many pages backed by a congested BDI were found during > scanning. If all the dirty pages encountered on a list isolated from the > LRU belong to a congested BDI, the zone is marked congested until the zone > reaches the high watermark. High watermark, or low watermark? The terms are rather ambiguous so let's avoid them. Maybe "full" watermark and "empty"? > > ... > > @@ -706,6 +726,7 @@ static unsigned long shrink_page_list(struct list_head *page_list, > goto keep; > > VM_BUG_ON(PageActive(page)); > + VM_BUG_ON(page_zone(page) != zone); ? > sc->nr_scanned++; > > > ... > > @@ -903,6 +928,15 @@ keep_lumpy: > VM_BUG_ON(PageLRU(page) || PageUnevictable(page)); > } > > + /* > + * Tag a zone as congested if all the dirty pages encountered were > + * backed by a congested BDI. In this case, reclaimers should just > + * back off and wait for congestion to clear because further reclaim > + * will encounter the same problem > + */ > + if (nr_dirty == nr_congested) > + zone_set_flag(zone, ZONE_CONGESTED); The implicit "100%" there is a magic number. hrm. -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>