Commit 4ffeaf35 (mm: page_alloc: reduce cost of the fair zone allocation policy)
broke the fair zone allocation policy on UP with these hunks.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6e5e8f7..fb99081 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1612,6 +1612,9 @@ again:
}
__mod_zone_page_state(zone, NR_ALLOC_BATCH, -(1 << order));
+ if (zone_page_state(zone, NR_ALLOC_BATCH) == 0 &&
+ !zone_is_fair_depleted(zone))
+ zone_set_flag(zone, ZONE_FAIR_DEPLETED);
__count_zone_vm_events(PGALLOC, zone, 1 << order);
zone_statistics(preferred_zone, zone, gfp_flags);
@@ -1966,8 +1985,10 @@ zonelist_scan:
if (alloc_flags & ALLOC_FAIR) {
if (!zone_local(preferred_zone, zone))
break;
- if (zone_page_state(zone, NR_ALLOC_BATCH) <= 0)
+ if (zone_is_fair_depleted(zone)) {
+ nr_fair_skipped++;
continue;
+ }
}
The problem is that a <= check was replaced with a ==. On SMP it doesn't
matter because negative values are returned as zero due to per-CPU drift
which is not possible in the UP case. Vlastimil Babka correctly pointed
out that this can be negative due to high-order allocations. This patch
fixes the problem.
Reported-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
mm/page_alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 18cee0d..cd4c05c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1612,7 +1612,7 @@ again:
}
__mod_zone_page_state(zone, NR_ALLOC_BATCH, -(1 << order));
- if (zone_page_state(zone, NR_ALLOC_BATCH) == 0 &&
+ if (zone_page_state(zone, NR_ALLOC_BATCH) <= 0 &&
!zone_is_fair_depleted(zone))
zone_set_flag(zone, ZONE_FAIR_DEPLETED);
--
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