[patch 1/9] oom: use unreclaimable info

[Nick Piggin <npiggin@suse.de>]

__alloc_pages currently starts shooting if page reclaim has failed to free up
swap_cluster_max pages in one run through the priorities. This is not always a
good indicator on its own, so make use of the all_unreclaimable logic as
well: don't consider going OOM until all zones we're interested in are
unreclaimable.

Signed-off-by: Nick Piggin <npiggin@suse.de>

Index: linux-2.6/mm/vmscan.c
===================================================================
--- linux-2.6.orig/mm/vmscan.c
+++ linux-2.6/mm/vmscan.c
@@ -62,6 +62,8 @@ struct scan_control {
 	int swap_cluster_max;
 
 	int swappiness;
+
+	int all_unreclaimable;
 };
 
 /*
@@ -925,6 +927,7 @@ static unsigned long shrink_zones(int pr
 	unsigned long nr_reclaimed = 0;
 	int i;
 
+	sc->all_unreclaimable = 1;
 	for (i = 0; zones[i] != NULL; i++) {
 		struct zone *zone = zones[i];
 
@@ -941,6 +944,8 @@ static unsigned long shrink_zones(int pr
 		if (zone->all_unreclaimable && priority != DEF_PRIORITY)
 			continue;	/* Let kswapd poll it */
 
+		sc->all_unreclaimable = 0;
+
 		nr_reclaimed += shrink_zone(priority, zone, sc);
 	}
 	return nr_reclaimed;
@@ -1021,6 +1026,9 @@ unsigned long try_to_free_pages(struct z
 		if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
 			blk_congestion_wait(WRITE, HZ/10);
 	}
+	/* top priority shrink_caches still had more to do? don't OOM, then */
+	if (!sc.all_unreclaimable)
+		ret = 1;
 out:
 	for (i = 0; zones[i] != 0; i++) {
 		struct zone *zone = zones[i];

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