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authorLinus Torvalds <torvalds@linux-foundation.org>2014-06-08 14:17:00 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-07-28 08:06:03 -0700
commit15c37d7780a8a807d778c57ca647beb2c8df4e71 (patch)
tree4e0c598390a5f573d60952e53b062ccf5a9be141
parent3e34e4d85a3918cc4e22e160ee843d28d1954103 (diff)
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Don't trigger congestion wait on dirty-but-not-writeout pages
commit b738d764652dc5aab1c8939f637112981fce9e0e upstream. 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 <felipe.contreras@gmail.com> Pinpointed-by: Hillf Danton <dhillf@gmail.com> Cc: Michal Hocko <mhocko@suse.cz> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Mel Gorman <mgorman@suse.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> [mhocko@suse.cz: backport to 3.12 stable tree] Fixes: e2be15f6c3ee ('mm: vmscan: stall page reclaim and writeback pages based on dirty/writepage pages encountered') Reported-by: Felipe Contreras <felipe.contreras@gmail.com> Pinpointed-by: Hillf Danton <dhillf@gmail.com> Cc: Michal Hocko <mhocko@suse.cz> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Mel Gorman <mgorman@suse.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Michal Hocko <mhocko@suse.cz> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--mm/vmscan.c11
1 files changed, 5 insertions, 6 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 6ef876cae8f1..6ef484f0777f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1540,19 +1540,18 @@ 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)
+ if (nr_immediate)
congestion_wait(BLK_RW_ASYNC, HZ/10);
}