[PATCH 7/8][for -mm] mem_notify v6: ignore very small zone for prevent incorrect low mem notify

["KOSAKI Motohiro" <kosaki.motohiro@jp.fujitsu.com>]

on X86, ZONE_DMA is very very small.
it cause undesirable low mem notification.
It should ignored.

but on other some architecture, ZONE_DMA have 4GB.
4GB is large as it is not possible to ignored.

therefore, ignore or not is decided by zone size.

ChangeLog:
	v5: new


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

---
 include/linux/mem_notify.h |    3 +++
 mm/page_alloc.c            |    6 +++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

Index: b/include/linux/mem_notify.h
===================================================================
--- a/include/linux/mem_notify.h	2008-01-23 22:06:04.000000000 +0900
+++ b/include/linux/mem_notify.h	2008-01-23 22:08:02.000000000 +0900
@@ -22,6 +22,9 @@ static inline void memory_pressure_notif
 	unsigned long target;
 	unsigned long pages_high, pages_free, pages_reserve;

+	if (unlikely(zone->mem_notify_status == -1))
+		return;
+
 	if (pressure) {
 		target = atomic_long_read(&last_mem_notify) + MEM_NOTIFY_FREQ;
 		if (likely(time_before(jiffies, target)))
Index: b/mm/page_alloc.c
===================================================================
--- a/mm/page_alloc.c	2008-01-23 22:07:57.000000000 +0900
+++ b/mm/page_alloc.c	2008-01-23 22:08:02.000000000 +0900
@@ -3470,7 +3470,11 @@ static void __meminit free_area_init_cor
 		zone->zone_pgdat = pgdat;

 		zone->prev_priority = DEF_PRIORITY;
-		zone->mem_notify_status = 0;
+
+		if (zone->present_pages < (pgdat->node_present_pages / 10))
+			zone->mem_notify_status = -1;
+		else
+			zone->mem_notify_status = 0;

 		zone_pcp_init(zone);
 		INIT_LIST_HEAD(&zone->active_list);