linux-kernel - Re: [PATCH v2 4/5] mm, kswapd: replace kswapd compaction with waking up kcompactd

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Date:	Wed, 2 Mar 2016 13:27:37 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrea Arcangeli <aarcange@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	David Rientjes <rientjes@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v2 4/5] mm, kswapd: replace kswapd compaction with waking
 up kcompactd

A fixlet for things Joonsoo caught.

----8<----
From: Vlastimil Babka <vbabka@...e.cz>
Date: Wed, 2 Mar 2016 11:50:16 +0100
Subject: mm-kswapd-replace-kswapd-compaction-with-waking-up-kcompactd-fix

Change zone_balanced() check in balance_pgdat() to consider only base pages
as that's the same what kswapd_shrink_zone() later does. So a zone that would
be selected due to lack of high-order pages would not be reclaimed anyway,
and just cause extra CPU churn.

Also remove unnecessary variable testorder in kswapd_shrink_zone().

Reported-by: Joonsoo Kim <iamjoonsoo.kim@....com>
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/vmscan.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index b8478a737ef5..23bc7e643ad8 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3073,7 +3073,6 @@ static bool kswapd_shrink_zone(struct zone *zone,
 			       int classzone_idx,
 			       struct scan_control *sc)
 {
-	int testorder = sc->order;
 	unsigned long balance_gap;
 	bool lowmem_pressure;
 
@@ -3094,7 +3093,7 @@ static bool kswapd_shrink_zone(struct zone *zone,
 	 * reclaim is necessary
 	 */
 	lowmem_pressure = (buffer_heads_over_limit && is_highmem(zone));
-	if (!lowmem_pressure && zone_balanced(zone, testorder, false,
+	if (!lowmem_pressure && zone_balanced(zone, sc->order, false,
 						balance_gap, classzone_idx))
 		return true;
 
@@ -3109,7 +3108,7 @@ static bool kswapd_shrink_zone(struct zone *zone,
 	 * waits.
 	 */
 	if (zone_reclaimable(zone) &&
-	    zone_balanced(zone, testorder, false, 0, classzone_idx)) {
+	    zone_balanced(zone, sc->order, false, 0, classzone_idx)) {
 		clear_bit(ZONE_CONGESTED, &zone->flags);
 		clear_bit(ZONE_DIRTY, &zone->flags);
 	}
@@ -3190,7 +3189,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
 				break;
 			}
 
-			if (!zone_balanced(zone, order, true, 0, 0)) {
+			if (!zone_balanced(zone, order, false, 0, 0)) {
 				end_zone = i;
 				break;
 			} else {
-- 
2.7.2