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Subject[PATCH 6/8][for -mm] mem_notify v6: (optional) fixed incorrect shrink_zone
on X86, ZONE_DMA is very very small.
It is often no used at all.

Unfortunately,
when NR_ACTIVE==0, NR_INACTIVE==0, shrink_zone() try to reclaim 1 page.
because

zone->nr_scan_active +=
(zone_page_state(zone, NR_ACTIVE) >> priority) + 1;
^^^^^
it cause unnecessary low memory notify ;-)
I fixed it.

ChangeLog
v5: new


Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

---
mm/vmscan.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)
Index: b/mm/vmscan.c
===================================================================
--- a/mm/vmscan.c 2008-02-03 20:27:53.000000000 +0900
+++ b/mm/vmscan.c 2008-02-03 20:33:13.000000000 +0900
@@ -947,7 +947,7 @@ static inline void note_zone_scanning_pr

static inline int zone_is_near_oom(struct zone *zone)
{
- return zone->pages_scanned >= (zone_page_state(zone, NR_ACTIVE)
+ return zone->pages_scanned > (zone_page_state(zone, NR_ACTIVE)
+ zone_page_state(zone, NR_INACTIVE))*3;
}

@@ -1196,18 +1196,29 @@ static unsigned long shrink_zone(int pri
unsigned long nr_inactive;
unsigned long nr_to_scan;
unsigned long nr_reclaimed = 0;
+ unsigned long tmp;
+ unsigned long zone_active;
+ unsigned long zone_inactive;

if (scan_global_lru(sc)) {
/*
* Add one to nr_to_scan just to make sure that the kernel
* will slowly sift through the active list.
*/
- zone->nr_scan_active +=
- (zone_page_state(zone, NR_ACTIVE) >> priority) + 1;
+ zone_active = zone_page_state(zone, NR_ACTIVE);
+ tmp = (zone_active >> priority) + 1;
+ if (unlikely(tmp > zone_active))
+ tmp = zone_active;
+ zone->nr_scan_active += tmp;
nr_active = zone->nr_scan_active;
- zone->nr_scan_inactive +=
- (zone_page_state(zone, NR_INACTIVE) >> priority) + 1;
+
+ zone_inactive = zone_page_state(zone, NR_INACTIVE);
+ tmp = (zone_inactive >> priority) + 1;
+ if (unlikely(tmp > zone_inactive))
+ tmp = zone_inactive;
+ zone->nr_scan_inactive += tmp;
nr_inactive = zone->nr_scan_inactive;
+
if (nr_inactive >= sc->swap_cluster_max)
zone->nr_scan_inactive = 0;
else

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