Re: 3.7-rc6 soft lockup in kswapd0

From: Johannes Weiner <hannes@cmpxchg.org>
Date: 2012-11-26 18:33:34
Also in: lkml
Subsystem: memory management, memory management - mglru (multi-gen lru), memory management - reclaim, the rest · Maintainers: Andrew Morton, Johannes Weiner, Linus Torvalds

Possibly related (same subject, not in this thread)

2012-11-23 · Re: 3.7-rc6 soft lockup in kswapd0 · Tomas Racek <hidden>

Hi George,

On Mon, Nov 26, 2012 at 08:05:04AM -0500, George Spelvin wrote:

Mel Gorman [off-list ref] wrote:

quoted

Ok, can you try this patch from Rik on top as well please? This is in
addition to Dave Hansen's accounting fix.

---8<---
From: Rik van Riel <redacted>
Subject: mm,vmscan: only loop back if compaction would fail in all zones

Booted and running.  Judging from the patch, the expected result is
"stops hanging", as opposed to more informative diagnostics, so I'll
keep you posted.

Peraonally, I like to use "bool" for such flags where possible;
it helps document the intent of the variable better.

Any chance you could test with this fix instead, in addition to Dave's
accounting fix?  It's got bool and everything!

---
From: Johannes Weiner <hannes@cmpxchg.org>
Subject: [patch] mm: vmscan: fix endless loop in kswapd balancing

Kswapd does not in all places have the same criteria for when it
considers a zone balanced.  This leads to zones being not reclaimed
because they are considered just fine and other checks to loop over
the zonelist again because they are considered unbalanced.

Add a function, zone_balanced(), that checks the watermark, and, for
higher order allocations, if compaction has enough free memory.  Then
use it uniformly for when kswapd needs to check if a zone is balanced.

Reported-by: George Spelvin <redacted>
Reported-by: Johannes Hirte <redacted>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Tested-by: Johannes Hirte <redacted>
Reviewed-by: Rik van Riel <redacted>
Cc: stable@kernel.org [3.4+]
---
 mm/vmscan.c | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 48550c6..3b0aef4 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -2397,6 +2397,19 @@ static void age_active_anon(struct zone *zone, struct scan_control *sc)
 	} while (memcg);
 }
 
+static bool zone_balanced(struct zone *zone, int order,
+			  unsigned long balance_gap, int classzone_idx)
+{
+	if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) +
+				    balance_gap, classzone_idx, 0))
+		return false;
+
+	if (COMPACTION_BUILD && order && !compaction_suitable(zone, order))
+		return false;
+
+	return true;
+}
+
 /*
  * pgdat_balanced is used when checking if a node is balanced for high-order
  * allocations. Only zones that meet watermarks and are in a zone allowed

@@ -2475,8 +2488,7 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
 			continue;
 		}
 
-		if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
-							i, 0))
+		if (!zone_balanced(zone, order, 0, i))
 			all_zones_ok = false;
 		else
 			balanced += zone->present_pages;

@@ -2585,8 +2597,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 				break;
 			}
 
-			if (!zone_watermark_ok_safe(zone, order,
-					high_wmark_pages(zone), 0, 0)) {
+			if (!zone_balanced(zone, order, 0, 0)) {
 				end_zone = i;
 				break;
 			} else {

@@ -2662,9 +2673,8 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 				testorder = 0;
 
 			if ((buffer_heads_over_limit && is_highmem_idx(i)) ||
-				    !zone_watermark_ok_safe(zone, testorder,
-					high_wmark_pages(zone) + balance_gap,
-					end_zone, 0)) {
+			    !zone_balanced(zone, testorder,
+					   balance_gap, end_zone)) {
 				shrink_zone(zone, &sc);
 
 				reclaim_state->reclaimed_slab = 0;

@@ -2691,8 +2701,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 				continue;
 			}
 
-			if (!zone_watermark_ok_safe(zone, testorder,
-					high_wmark_pages(zone), end_zone, 0)) {
+			if (!zone_balanced(zone, testorder, 0, end_zone)) {
 				all_zones_ok = 0;
 				/*
 				 * We are still under min water mark.  This

-- 
1.7.11.7

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