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 <mgor...@suse.de>
---
mm/vmscan.c | 60 ++++++++++++++++++++++++++++++------------------------------
1 file changed, 30 insertions(+), 30 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 78268ca..a9e68b4 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2640,7 +2640,8 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int
order, long remaining,
*/
static bool kswapd_shrink_zone(struct zone *zone,
struct scan_control *sc,
- unsigned long lru_pages)
+ unsigned long lru_pages,
+ unsigned long *nr_attempted)
{
unsigned long nr_slab;
struct reclaim_state *reclaim_state = current->reclaim_state;
@@ -2656,6 +2657,9 @@ static bool kswapd_shrink_zone(struct zone *zone,
nr_slab = shrink_slab(&shrink, sc->nr_scanned, lru_pages);
sc->nr_reclaimed += reclaim_state->reclaimed_slab;
+ /* Account for the number of pages attempted to reclaim */
+ *nr_attempted += sc->nr_to_reclaim;
+
if (nr_slab == 0 && !zone_reclaimable(zone))
zone->all_unreclaimable = 1;
@@ -2703,8 +2707,11 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int
order,
do {
unsigned long lru_pages = 0;
+ unsigned long nr_attempted = 0;
unsigned long nr_reclaimed = sc.nr_reclaimed = 0;
+ unsigned long this_reclaimed;
bool raise_priority = true;
+ bool pgdat_needs_compaction = (order > 0);
/*
* Scan in the highmem->dma direction for the highest
@@ -2752,7 +2759,21 @@ 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);
+
+ /*
+ * If any zone is currently balanced then kswapd will
+ * not call compaction as it is expected that the
+ * necessary pages are already available.
+ */
+ if (pgdat_needs_compaction &&
+ zone_watermark_ok(zone, order,
+ low_wmark_pages(zone),
+ *classzone_idx, 0))
+ pgdat_needs_compaction = false;
}
/*
@@ -2821,7 +2842,8 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int
order,
* already being scanned that high
* watermark would be met at 100% efficiency.
*/
- if (kswapd_shrink_zone(zone, &sc, lru_pages))
+ if (kswapd_shrink_zone(zone, &sc, lru_pages,
+ &nr_attempted))
raise_priority = false;
}
@@ -2873,42 +2895,20 @@ static unsigned long balance_pgdat(pg_data_t *pgdat,
int order,
if (try_to_freeze() || kthread_should_stop())
break;
+ /* Compact if necessary and kswapd is reclaiming efficiently */
+ this_reclaimed = sc.nr_reclaimed - nr_reclaimed;
+ if (pgdat_needs_compaction && this_reclaimed > nr_attempted)
+ 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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