For 32-bit machines rollback the default number of vnode pager pbufs

back to the lever before r343030.  For 64-bit machines reduce it slightly,
too.  Together with r343030 I bumped the limit up to the value we use at
Netflix to serve 100 Gbit/s of sendfile traffic, and it probably isn't a
good default.

Provide a loader tunable to change vnode pager pbufs count. Document it.

1 files changed, 11 insertions, 1 deletions

diff --git a/sys/vm/vnode_pager.c b/sys/vm/vnode_pager.c
index 3e71ab4436cc..ded9e65e4e4c 100644
--- a/sys/vm/vnode_pager.c
+++ b/sys/vm/vnode_pager.c
@@ -115,13 +115,23 @@ SYSCTL_PROC(_debug, OID_AUTO, vnode_domainset, CTLTYPE_STRING | CTLFLAG_RW,
     &vnode_domainset, 0, sysctl_handle_domainset, "A",
     "Default vnode NUMA policy");
 
+static int nvnpbufs;
+SYSCTL_INT(_vm, OID_AUTO, vnode_pbufs, CTLFLAG_RDTUN | CTLFLAG_NOFETCH,
+    &nvnpbufs, 0, "number of physical buffers allocated for vnode pager");
+
 static uma_zone_t vnode_pbuf_zone;
 
 static void
 vnode_pager_init(void *dummy)
 {
 
-	vnode_pbuf_zone = pbuf_zsecond_create("vnpbuf", nswbuf * 8);
+#ifdef __LP64__
+	nvnpbufs = nswbuf * 2;
+#else
+	nvnpbufs = nswbuf / 2;
+#endif
+	TUNABLE_INT_FETCH("vm.vnode_pbufs", &nvnpbufs);
+	vnode_pbuf_zone = pbuf_zsecond_create("vnpbuf", nvnpbufs);
 }
 SYSINIT(vnode_pager, SI_SUB_CPU, SI_ORDER_ANY, vnode_pager_init, NULL);