From: Linus Torvalds Date: Sun, 8 Jun 2014 21:17:00 +0000 (-0700) Subject: Don't trigger congestion wait on dirty-but-not-writeout pages X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=b738d764652dc5aab1c8939f637112981fce9e0e;p=openwrt%2Fstaging%2Fblogic.git Don't trigger congestion wait on dirty-but-not-writeout pages shrink_inactive_list() used to wait 0.1s to avoid congestion when all the pages that were isolated from the inactive list were dirty but not under active writeback. That makes no real sense, and apparently causes major interactivity issues under some loads since 3.11. The ostensible reason for it was to wait for kswapd to start writing pages, but that seems questionable as well, since the congestion wait code seems to trigger for kswapd itself as well. Also, the logic behind delaying anything when we haven't actually started writeback is not clear - it only delays actually starting that writeback. We'll still trigger the congestion waiting if (a) the process is kswapd, and we hit pages flagged for immediate reclaim (b) the process is not kswapd, and the zone backing dev writeback is actually congested. This probably needs to be revisited, but as it is this fixes a reported regression. Reported-by: Felipe Contreras Pinpointed-by: Hillf Danton Cc: Michal Hocko Cc: Andrew Morton Cc: Mel Gorman Signed-off-by: Linus Torvalds --- diff --git a/mm/vmscan.c b/mm/vmscan.c index 71f23c0c1090..e01ded365440 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1573,20 +1573,18 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec, * If dirty pages are scanned that are not queued for IO, it * implies that flushers are not keeping up. In this case, flag * the zone ZONE_TAIL_LRU_DIRTY and kswapd will start writing - * pages from reclaim context. It will forcibly stall in the - * next check. + * pages from reclaim context. */ if (nr_unqueued_dirty == nr_taken) zone_set_flag(zone, ZONE_TAIL_LRU_DIRTY); /* - * In addition, if kswapd scans pages marked marked for - * immediate reclaim and under writeback (nr_immediate), it - * implies that pages are cycling through the LRU faster than + * If kswapd scans pages marked marked for immediate + * reclaim and under writeback (nr_immediate), it implies + * that pages are cycling through the LRU faster than * they are written so also forcibly stall. */ - if ((nr_unqueued_dirty == nr_taken || nr_immediate) && - current_may_throttle()) + if (nr_immediate && current_may_throttle()) congestion_wait(BLK_RW_ASYNC, HZ/10); }