[PATCH 6/6] mm: kswapd: Use the classzone idx that kswapd was using for sleeping_prematurely()

[Mel Gorman]

When kswapd is woken up for a high-order allocation, it takes account of
the highest usable zone by the caller (the classzone idx). During
allocation, this index is used to select the lowmem_reserve[] that
should be applied to the watermark calculation in zone_watermark_ok().

When balancing a node, kswapd considers the highest unbalanced zone to be the
classzone index. This will always be at least be the callers classzone_idx
and can be higher. However, sleeping_prematurely() always considers the
lowest zone (e.g. ZONE_DMA) to be the classzone index. This means that
sleeping_prematurely() can consider a zone to be balanced that is unusable
by the allocation request that originally woke kswapd. This patch changes
sleeping_prematurely() to use a classzone_idx matching the value it used
in balance_pgdat().

Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
---
 mm/vmscan.c |   19 +++++++++++--------
 1 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index d7b0a3c..e25b3ac 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2132,7 +2132,8 @@ static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced)
 }
 
 /* is kswapd sleeping prematurely? */
-static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
+static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
+					int classzone_idx)
 {
 	int i;
 	unsigned long balanced = 0;
@@ -2140,7 +2141,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
 
 	/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
 	if (remaining)
-		return 1;
+		return true;
 
 	/* Check the watermark levels */
 	for (i = 0; i < pgdat->nr_zones; i++) {
@@ -2161,7 +2162,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
 		}
 
 		if (!zone_watermark_ok(zone, order, high_wmark_pages(zone),
-								0, 0))
+							classzone_idx, 0))
 			all_zones_ok = false;
 		else
 			balanced += zone->present_pages;
@@ -2199,7 +2200,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
  * of pages is balanced across the zones.
  */
 static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
-							int classzone_idx)
+							int *classzone_idx)
 {
 	int all_zones_ok;
 	unsigned long balanced;
@@ -2262,6 +2263,7 @@ loop_again:
 			if (!zone_watermark_ok(zone, order,
 					high_wmark_pages(zone), 0, 0)) {
 				end_zone = i;
+				*classzone_idx = i;
 				break;
 			}
 		}
@@ -2346,7 +2348,7 @@ loop_again:
 				 * spectulatively avoid congestion waits
 				 */
 				zone_clear_flag(zone, ZONE_CONGESTED);
-				if (i <= classzone_idx)
+				if (i <= *classzone_idx)
 					balanced += zone->present_pages;
 			}
 
@@ -2441,6 +2443,7 @@ out:
 	 * if another caller entered the allocator slow path while kswapd
 	 * was awake, order will remain at the higher level
 	 */
+	*classzone_idx = end_zone;
 	return order;
 }
 
@@ -2514,7 +2517,7 @@ static int kswapd(void *p)
 				long remaining = 0;
 
 				/* Try to sleep for a short interval */
-				if (!sleeping_prematurely(pgdat, order, remaining)) {
+				if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
 					remaining = schedule_timeout(HZ/10);
 					finish_wait(&pgdat->kswapd_wait, &wait);
 					prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
@@ -2525,7 +2528,7 @@ static int kswapd(void *p)
 				 * premature sleep. If not, then go fully
 				 * to sleep until explicitly woken up
 				 */
-				if (!sleeping_prematurely(pgdat, order, remaining)) {
+				if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
 					trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
 					schedule();
 				} else {
@@ -2553,7 +2556,7 @@ static int kswapd(void *p)
 		 */
 		if (!ret) {
 			trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
-			order = balance_pgdat(pgdat, order, classzone_idx);
+			order = balance_pgdat(pgdat, order, &classzone_idx);
 		}
 	}
 	return 0;
-- 
1.7.1

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