Index: sys/vm/vm_pageout.c
===================================================================
--- sys/vm/vm_pageout.c	(revision 271156)
+++ sys/vm/vm_pageout.c	(working copy)
@@ -76,6 +76,7 @@
 __FBSDID("$FreeBSD$");
 
 #include "opt_vm.h"
+#include "opt_kdtrace.h"
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/kernel.h>
@@ -89,6 +90,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/racct.h>
 #include <sys/resourcevar.h>
 #include <sys/sched.h>
+#include <sys/sdt.h>
 #include <sys/signalvar.h>
 #include <sys/smp.h>
 #include <sys/vnode.h>
@@ -133,6 +135,10 @@ static struct kproc_desc page_kp = {
 SYSINIT(pagedaemon, SI_SUB_KTHREAD_PAGE, SI_ORDER_SECOND, kproc_start,
     &page_kp);
 
+SDT_PROVIDER_DEFINE(vm);
+SDT_PROBE_DEFINE(vm, , , vm__lowmem_cache);
+SDT_PROBE_DEFINE(vm, , , vm__lowmem_scan);
+
 #if !defined(NO_SWAPPING)
 /* the kernel process "vm_daemon"*/
 static void vm_daemon(void);
@@ -667,6 +673,7 @@ vm_pageout_grow_cache(int tries, vm_paddr_t low, v
 		 * may acquire locks and/or sleep, so they can only be invoked
 		 * when "tries" is greater than zero.
 		 */
+		SDT_PROBE0(vm, , , vm__lowmem_cache);
 		EVENTHANDLER_INVOKE(vm_lowmem, 0);
 
 		/*
@@ -899,7 +906,7 @@ vm_pageout_map_deactivate_pages(map, desired)
  *	pass 1 - Move inactive to cache or free
  *	pass 2 - Launder dirty pages
  */
-static void
+static void __used
 vm_pageout_scan(struct vm_domain *vmd, int pass)
 {
 	vm_page_t m, next;
@@ -920,6 +927,7 @@ vm_pageout_scan(struct vm_domain *vmd, int pass)
 		/*
 		 * Decrease registered cache sizes.
 		 */
+		SDT_PROBE0(vm, , , vm__lowmem_scan);
 		EVENTHANDLER_INVOKE(vm_lowmem, 0);
 		/*
 		 * We do this explicitly after the caches have been