On 06/09/2016 08:04 PM, Mel Gorman wrote:
kswapd scans from highest to lowest for a zone that requires balancing.
This was necessary when reclaim was per-zone to fairly age pages on
lower zones. Now that we are reclaiming on a per-node basis, any eligible
zone can be used and pages will still be aged fairly. This patch avoids
reclaiming excessively unless buffer_heads are over the limit and it's
necessary to reclaim from a higher zone than requested by the waker of
kswapd to relieve low memory pressure.
Looks like the code was even wrong before... if classzone_idx wasn't
already set to the highmem zone in the first place, it wouldn't look at it.
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
After fixing the bug below,
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
---
mm/vmscan.c | 32 +++++++++++++++++++-------------
1 file changed, 19 insertions(+), 13 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index e4f3e068b7a0..6663fc75c3bc 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3102,24 +3102,30 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
sc.nr_reclaimed = 0;
- /* Scan from the highest requested zone to dma */
+ /*
+ * If the number of buffer_heads in the machine exceeds the
+ * maximum allowed level and this node has a highmem zone,
+ * force kswapd to reclaim from it to relieve lowmem pressure.
+ */
+ if (buffer_heads_over_limit) {
+ for (i = MAX_NR_ZONES - 1; i >= 0; i++) {
i--
+ zone = pgdat->node_zones + i;
+ if (!populated_zone(zone))
+ continue;
+
+ if (is_highmem_idx(i))
+ classzone_idx = i;
+ break;
+ }
+ }
+
+ /* Only reclaim if there are no eligible zones */
for (i = classzone_idx; i >= 0; i--) {
zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
- /*
- * If the number of buffer_heads in the machine
- * exceeds the maximum allowed level and this node
- * has a highmem zone, force kswapd to reclaim from
- * it to relieve lowmem pressure.
- */
- if (buffer_heads_over_limit && is_highmem_idx(i)) {
- classzone_idx = i;
- break;
- }
-
- if (!zone_balanced(zone, order, 0)) {
+ if (!zone_balanced(zone, sc.order, classzone_idx)) {
classzone_idx = i;
break;
}
--
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