In the past, kswapd makes a decision on whether to compact memory after the
pgdat was considered balanced. This more or less worked but it is late to
make such a decision and does not fit well now that kswapd makes a decision
whether to exit the zone scanning loop depending on reclaim progress.
This patch will compact a pgdat if at least the requested number of pages
were reclaimed from unbalanced zones for a given priority. If any zone is
currently balanced, kswapd will not call compaction as it is expected the
necessary pages are already available.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
mm/vmscan.c | 52 +++++++++++++++++++++-------------------------------
1 file changed, 21 insertions(+), 31 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 279d0c2..7513bd1 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2694,8 +2694,11 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
do {
unsigned long lru_pages = 0;
+ unsigned long nr_to_reclaim = 0;
unsigned long nr_reclaimed = sc.nr_reclaimed;
+ unsigned long this_reclaimed;
bool raise_priority = true;
+ bool pgdat_needs_compaction = true;
/*
* Scan in the highmem->dma direction for the highest
@@ -2743,7 +2746,17 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
for (i = 0; i <= end_zone; i++) {
struct zone *zone = pgdat->node_zones + i;
+ if (!populated_zone(zone))
+ continue;
+
lru_pages += zone_reclaimable_pages(zone);
+
+ /* Check if the memory needs to be defragmented */
+ if (order && pgdat_needs_compaction &&
+ zone_watermark_ok(zone, order,
+ low_wmark_pages(zone),
+ *classzone_idx, 0))
+ pgdat_needs_compaction = false;
}
/*
@@ -2814,6 +2827,8 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
*/
if (kswapd_shrink_zone(zone, &sc, lru_pages))
raise_priority = false;
+
+ nr_to_reclaim += sc.nr_to_reclaim;
}
/*
@@ -2864,46 +2879,21 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
if (try_to_freeze() || kthread_should_stop())
break;
- /* If no reclaim progress then increase scanning priority */
- if (sc.nr_reclaimed - nr_reclaimed == 0)
- raise_priority = true;
+ /* Compact if necessary and kswapd is reclaiming efficiently */
+ this_reclaimed = sc.nr_reclaimed - nr_reclaimed;
+ if (order && pgdat_needs_compaction &&
+ this_reclaimed > nr_to_reclaim)
+ compact_pgdat(pgdat, order);
/*
* Raise priority if scanning rate is too low or there was no
* progress in reclaiming pages
*/
- if (raise_priority || sc.nr_reclaimed - nr_reclaimed == 0)
+ if (raise_priority || !this_reclaimed)
sc.priority--;
} while (sc.priority >= 0 &&
!pgdat_balanced(pgdat, order, *classzone_idx));
- /*
- * If kswapd was reclaiming at a higher order, it has the option of
- * sleeping without all zones being balanced. Before it does, it must
- * ensure that the watermarks for order-0 on *all* zones are met and
- * that the congestion flags are cleared. The congestion flag must
- * be cleared as kswapd is the only mechanism that clears the flag
- * and it is potentially going to sleep here.
- */
- if (order) {
- int zones_need_compaction = 1;
-
- for (i = 0; i <= end_zone; i++) {
- struct zone *zone = pgdat->node_zones + i;
-
- if (!populated_zone(zone))
- continue;
-
- /* Check if the memory needs to be defragmented. */
- if (zone_watermark_ok(zone, order,
- low_wmark_pages(zone), *classzone_idx, 0))
- zones_need_compaction = 0;
- }
-
- if (zones_need_compaction)
- compact_pgdat(pgdat, order);
- }
-
out:
/*
* Return the order we were reclaiming at so prepare_kswapd_sleep()
--
1.8.1.4
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