Index: sys/pool.h
===================================================================
RCS file: /cvs/src/sys/sys/pool.h,v
retrieving revision 1.71
diff -u -p -r1.71 pool.h
--- sys/pool.h	16 Jun 2017 01:55:45 -0000	1.71
+++ sys/pool.h	16 Jun 2017 03:03:03 -0000
@@ -189,6 +189,7 @@ struct pool {
 	u_int		pr_cache_nlist;	/* # of idle lists */
 	u_int		pr_cache_items;	/* target list length */
 	u_int		pr_cache_contention;
+	u_int		pr_cache_contention_prev;
 	int		pr_cache_tick;	/* time idle list was empty */
 	int		pr_cache_nout;
 	uint64_t	pr_cache_ngc;	/* # of times the gc released a list */
Index: kern/subr_pool.c
===================================================================
RCS file: /cvs/src/sys/kern/subr_pool.c,v
retrieving revision 1.214
diff -u -p -r1.214 subr_pool.c
--- kern/subr_pool.c	16 Jun 2017 01:55:45 -0000	1.214
+++ kern/subr_pool.c	16 Jun 2017 03:03:03 -0000
@@ -1926,6 +1926,8 @@ pool_cache_destroy(struct pool *pp)
 void
 pool_cache_gc(struct pool *pp)
 {
+	unsigned int contention;
+
 	if ((ticks - pp->pr_cache_tick) > (hz * pool_wait_gc) &&
 	    !TAILQ_EMPTY(&pp->pr_cache_lists) &&
 	    mtx_enter_try(&pp->pr_cache_mtx)) {
@@ -1944,6 +1946,25 @@ pool_cache_gc(struct pool *pp)
 
 		pool_cache_list_put(pp, pl);
 	}
+
+	/*
+	 * if there's a lot of contention on the pr_cache_mtx then consider
+	 * growing the length of the list to reduce the need to access the
+	 * global pool.
+	 */
+
+	contention = pp->pr_cache_contention;
+	if ((contention - pp->pr_cache_contention_prev) > 8 /* magic */) {
+		unsigned int limit = pp->pr_npages * pp->pr_itemsperpage;
+		unsigned int items = pp->pr_cache_items + 8;
+		unsigned int cache = ncpusfound * items * 2;
+
+		/* are there enough items around so every cpu can hold some? */
+
+		if (cache < limit)
+			pp->pr_cache_items += items;
+	}
+	pp->pr_cache_contention_prev = contention;
 }
 
 void