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-rw-r--r--mm/vmscan.c22
1 files changed, 14 insertions, 8 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1f35364e0feb..b3829c7e3a7d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3123,7 +3123,6 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
.may_writepage = !laptop_mode,
.may_unmap = 1,
.may_swap = 1,
- .reclaim_idx = classzone_idx,
};
count_vm_event(PAGEOUTRUN);
@@ -3131,12 +3130,17 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
bool raise_priority = true;
sc.nr_reclaimed = 0;
+ sc.reclaim_idx = classzone_idx;
/*
- * If the number of buffer_heads in the machine exceeds the
- * maximum allowed level then reclaim from all zones. This is
- * not specific to highmem as highmem may not exist but it is
- * it is expected that buffer_heads are stripped in writeback.
+ * If the number of buffer_heads exceeds the maximum allowed
+ * then consider reclaiming from all zones. This has a dual
+ * purpose -- on 64-bit systems it is expected that
+ * buffer_heads are stripped during active rotation. On 32-bit
+ * systems, highmem pages can pin lowmem memory and shrinking
+ * buffers can relieve lowmem pressure. Reclaim may still not
+ * go ahead if all eligible zones for the original allocation
+ * request are balanced to avoid excessive reclaim from kswapd.
*/
if (buffer_heads_over_limit) {
for (i = MAX_NR_ZONES - 1; i >= 0; i--) {
@@ -3155,14 +3159,16 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
* Scanning from low to high zone would allow congestion to be
* cleared during a very small window when a small low
* zone was balanced even under extreme pressure when the
- * overall node may be congested.
+ * overall node may be congested. Note that sc.reclaim_idx
+ * is not used as buffer_heads_over_limit may have adjusted
+ * it.
*/
- for (i = sc.reclaim_idx; i >= 0; i--) {
+ for (i = classzone_idx; i >= 0; i--) {
zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
- if (zone_balanced(zone, sc.order, sc.reclaim_idx))
+ if (zone_balanced(zone, sc.order, classzone_idx))
goto out;
}