mm: vmscan: do not keep kswapd looping forever due to individual uncompactable zones

hnaz · torvalds · commit c702418f8a2f · 2012-12-06T11:29:57.000-08:00
When a zone meets its high watermark and is compactable in case of higher order allocations, it contributes to the percentage of the node's memory that is considered balanced. This requirement, that a node be only partially balanced, came about when kswapd was desparately trying to balance tiny zones when all bigger zones in the node had plenty of free memory. Arguably, the same should apply to compaction: if a significant part of the node is balanced enough to run compaction, do not get hung up on that tiny zone that might never get in shape. When the compaction logic in kswapd is reached, we know that at least 25% of the node's memory is balanced properly for compaction (see zone_balanced and pgdat_balanced). Remove the individual zone checks that restart the kswapd cycle. Otherwise, we may observe more endless looping in kswapd where the compaction code loops back to reclaim because of a single zone and reclaim does nothing because the node is considered balanced overall. See for example https://bugzilla.redhat.com/show_bug.cgi?id=866988 Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Reported-and-tested-by: Thorsten Leemhuis <fedora@leemhuis.info> Reported-by: Jiri Slaby <jslaby@suse.cz> Tested-by: John Ellson <john.ellson@comcast.net> Tested-by: Zdenek Kabelac <zkabelac@redhat.com> Tested-by: Bruno Wolff III <bruno@wolff.to> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/vmscan.c b/mm/vmscan.c
@@ -2823,22 +2823,6 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 			if (!populated_zone(zone))
 				continue;
 
-			if (zone->all_unreclaimable &&
-			    sc.priority != DEF_PRIORITY)
-				continue;
-
-			/* Would compaction fail due to lack of free memory? */
-			if (COMPACTION_BUILD &&
-			    compaction_suitable(zone, order) == COMPACT_SKIPPED)
-				goto loop_again;
-
-			/* Confirm the zone is balanced for order-0 */
-			if (!zone_watermark_ok(zone, 0,
-					high_wmark_pages(zone), 0, 0)) {
-				order = sc.order = 0;
-				goto loop_again;
-			}
-
 			/* Check if the memory needs to be defragmented. */
 			if (zone_watermark_ok(zone, order,
 				    low_wmark_pages(zone), *classzone_idx, 0))
