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Subject[PATCH 3/6] mm: kswapd: Use the order that kswapd was reclaiming at for sleeping_prematurely()
Date
Before kswapd goes to sleep, it uses sleeping_prematurely() to check if
there was a race pushing a zone below its watermark. If the race
happened, it stays awake. However, balance_pgdat() can decide to reclaim
at a lower order if it decides that high-order reclaim is not working as
expected. This information is not passed back to sleeping_prematurely().
The impact is that kswapd remains awake reclaiming pages long after it
should have gone to sleep. This patch passes the adjusted order to
sleeping_prematurely and uses the same logic as balance_pgdat to decide
if it's ok to go to sleep.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
---
mm/vmscan.c | 14 ++++++++++----
1 files changed, 10 insertions(+), 4 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b4472a1..52e229e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2132,7 +2132,7 @@ static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced)
}

/* is kswapd sleeping prematurely? */
-static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
+static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
{
int i;
unsigned long balanced = 0;
@@ -2142,7 +2142,7 @@ static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
if (remaining)
return 1;

- /* If after HZ/10, a zone is below the high mark, it's premature */
+ /* Check the watermark levels */
for (i = 0; i < pgdat->nr_zones; i++) {
struct zone *zone = pgdat->node_zones + i;

@@ -2427,7 +2427,13 @@ out:
}
}

- return sc.nr_reclaimed;
+ /*
+ * Return the order we were reclaiming at so sleeping_prematurely()
+ * makes a decision on the order we were last reclaiming at. However,
+ * if another caller entered the allocator slow path while kswapd
+ * was awake, order will remain at the higher level
+ */
+ return order;
}

/*
@@ -2537,7 +2543,7 @@ static int kswapd(void *p)
*/
if (!ret) {
trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
- balance_pgdat(pgdat, order, classzone_idx);
+ order = balance_pgdat(pgdat, order, classzone_idx);
}
}
return 0;
--
1.7.1


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