MFC r258336:

Implement soft pressure on UMA cache bucket sizes.

Every time system detects low memory condition decrease bucket sizes for
each zone by one item.  As result, higher memory pressure will push to
smaller bucket sizes and so smaller per-CPU caches and so more efficient
memory use.

Before this change there was no force to oppose buckets growth as result
of practically inevitable zone lock conflicts, and after some run time
per-CPU caches could consume enough RAM to kill the system.

2 files changed, 11 insertions, 1 deletions

diff --git a/sys/vm/uma_core.c b/sys/vm/uma_core.c
index 85c96e5..7ad6e84 100644
--- a/sys/vm/uma_core.c
+++ b/sys/vm/uma_core.c
@@ -702,6 +702,13 @@ bucket_cache_drain(uma_zone_t zone)
 		bucket_free(zone, bucket, NULL);
 		ZONE_LOCK(zone);
 	}
+
+	/*
+	 * Shrink further bucket sizes.  Price of single zone lock collision
+	 * is probably lower then price of global cache drain.
+	 */
+	if (zone->uz_count > zone->uz_count_min)
+		zone->uz_count--;
 }
 
 static void
@@ -1462,6 +1469,7 @@ zone_ctor(void *mem, int size, void *udata, int flags)
 	zone->uz_fails = 0;
 	zone->uz_sleeps = 0;
 	zone->uz_count = 0;
+	zone->uz_count_min = 0;
 	zone->uz_flags = 0;
 	zone->uz_warning = NULL;
 	timevalclear(&zone->uz_ratecheck);
@@ -1553,6 +1561,7 @@ out:
 		zone->uz_count = bucket_select(zone->uz_size);
 	else
 		zone->uz_count = BUCKET_MAX;
+	zone->uz_count_min = zone->uz_count;
 
 	return (0);
 }
diff --git a/sys/vm/uma_int.h b/sys/vm/uma_int.h
index 00e8519..1ffc7d5 100644
--- a/sys/vm/uma_int.h
+++ b/sys/vm/uma_int.h
@@ -300,7 +300,8 @@ struct uma_zone {
 	volatile u_long	uz_fails;	/* Total number of alloc failures */
 	volatile u_long	uz_frees;	/* Total number of frees */
 	uint64_t	uz_sleeps;	/* Total number of alloc sleeps */
-	uint16_t	uz_count;	/* Highest amount of items in bucket */
+	uint16_t	uz_count;	/* Amount of items in full bucket */
+	uint16_t	uz_count_min;	/* Minimal amount of items there */
 
 	/* The next three fields are used to print a rate-limited warnings. */
 	const char	*uz_warning;	/* Warning to print on failure */