On Thu, 04 Nov 2010 08:50:58 +0800 Shaohua Li <shaohua.li@xxxxxxxxx> wrote: > nr_dirty and nr_congested are increased only when page is dirty. So if all pages > are clean, both them will be zero. In this case, we should not mark the zone > congested. > > Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx> > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index b8a6fdc..d31d7ce 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -913,7 +913,7 @@ keep_lumpy: > * back off and wait for congestion to clear because further reclaim > * will encounter the same problem > */ > - if (nr_dirty == nr_congested) > + if (nr_dirty == nr_congested && nr_dirty != 0) > zone_set_flag(zone, ZONE_CONGESTED); > > free_page_list(&free_pages); In a way, this was a really big bug. Reclaim will set the zone as congested a *lot* - when reclaiming simple, clean pagecache. It does appear that kswapd will unset it a lot too, so the net effect isn't obvious. However most of the time, the atomic_read(&nr_bdi_congested[sync]) in wait_iff_congested() will prevent this bug from causing harm. btw, it's irritating that we have this asymmetry: setter: zone_set_flag(zone, ZONE_CONGESTED) getter: zone_is_reclaim_congested(zone) -- 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 policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>