On Wed, Jan 26, 2011 at 04:36:55PM +0000, Mel Gorman wrote:
> > But the wmarks don't
> > seem the real offender, maybe it's something related to the tiny pci32
> > zone that materialize on 4g systems that relocate some little memory
> > over 4g to make space for the pci32 mmio. I didn't yet finish to debug
> > it.
> >
>
> This has to be it. What I think is happening is that we're in balance_pgdat(),
> the "Normal" zone is never hitting the watermark and we constantly call
> "goto loop_again" trying to "rebalance" all zones.
>
Confirmed. The following "patch" should fix allow the number of free pages to
drop to a sensible level. Note, this is not intended as a fix because it's
the utterly wrong approach to take. It's only to illustrate where things
are going wrong when the top-most zone is very small.
diff --git a/mm/vmscan.c b/mm/vmscan.c
index f5d90de..477cb77 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2259,7 +2259,8 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
}
if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
- classzone_idx, 0))
+ classzone_idx, 0) &&
+ zone->present_pages >= pgdat->node_present_pages >> 2)
all_zones_ok = false;
else
balanced += zone->present_pages;
@@ -2446,15 +2447,18 @@ loop_again:
if (!zone_watermark_ok_safe(zone, order,
high_wmark_pages(zone), end_zone, 0)) {
- all_zones_ok = 0;
- /*
- * We are still under min water mark. This
- * means that we have a GFP_ATOMIC allocation
- * failure risk. Hurry up!
- */
- if (!zone_watermark_ok_safe(zone, order,
- min_wmark_pages(zone), end_zone, 0))
- has_under_min_watermark_zone = 1;
+ if (zone->present_pages >= pgdat->node_present_pages >> 2) {
+ all_zones_ok = 0;
+
+ /*
+ * We are still under min water mark. This
+ * means that we have a GFP_ATOMIC allocation
+ * failure risk. Hurry up!
+ */
+ if (!zone_watermark_ok_safe(zone, order,
+ min_wmark_pages(zone), end_zone, 0))
+ has_under_min_watermark_zone = 1;
+ }
} else {
/*
* If a zone reaches its high watermark,
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