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Subject[PATCH] mm: limit lowmem_reserve
Date
It is possible with a low enough lowmem_reserve ratio to make
zone_watermark_ok always fail if the lower_zone is small enough.
Impose a lower limit on the ratio to only allow 1/4 of the lower_zone
size to be set as lowmem_reserve. This limit is hit in ZONE_DMA by changing
the default vmsplit on i386 even without changing the default sysctl values.

Signed-off-by: Con Kolivas <kernel@kolivas.org>

---
mm/page_alloc.c | 24 +++++++++++++++++++++---
1 files changed, 21 insertions(+), 3 deletions(-)

Index: linux-2.6.17-rc1-mm1/mm/page_alloc.c
===================================================================
--- linux-2.6.17-rc1-mm1.orig/mm/page_alloc.c 2006-04-06 10:32:31.000000000 +1000
+++ linux-2.6.17-rc1-mm1/mm/page_alloc.c 2006-04-06 11:09:17.000000000 +1000
@@ -2566,14 +2566,32 @@ static void setup_per_zone_lowmem_reserv
zone->lowmem_reserve[j] = 0;

for (idx = j-1; idx >= 0; idx--) {
+ unsigned long max_reserve;
+ unsigned long reserve;
struct zone *lower_zone;

+ lower_zone = pgdat->node_zones + idx;
+ /*
+ * Put an upper limit on the reserve at 1/4
+ * the lower_zone size. This prevents large
+ * zone size differences such as 3G VMSPLIT
+ * or low sysctl values from making
+ * zone_watermark_ok always fail. This
+ * enforces a lower limit on the reserve_ratio
+ */
+ max_reserve = lower_zone->present_pages / 4;
+
if (sysctl_lowmem_reserve_ratio[idx] < 1)
sysctl_lowmem_reserve_ratio[idx] = 1;
-
- lower_zone = pgdat->node_zones + idx;
- lower_zone->lowmem_reserve[j] = present_pages /
+ reserve = present_pages /
sysctl_lowmem_reserve_ratio[idx];
+ if (reserve > max_reserve) {
+ reserve = max_reserve;
+ sysctl_lowmem_reserve_ratio[idx] =
+ present_pages / max_reserve;
+ }
+
+ lower_zone->lowmem_reserve[j] = reserve;
present_pages += lower_zone->present_pages;
}
}
-
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