1 files changed, 22 insertions, 4 deletions

diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index 5fa1f80671cd..2c89cd949c5b 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -760,17 +760,36 @@ vm_page_trysbusy(vm_page_t m)
 }
 
 static void
+vm_page_xunbusy_locked(vm_page_t m)
+{
+
+	vm_page_assert_xbusied(m);
+	vm_page_assert_locked(m);
+
+	atomic_store_rel_int(&m->busy_lock, VPB_UNBUSIED);
+	/* There is a waiter, do wakeup() instead of vm_page_flash(). */
+	wakeup(m);
+}
+
+static void
 vm_page_xunbusy_maybelocked(vm_page_t m)
 {
 	bool lockacq;
 
 	vm_page_assert_xbusied(m);
 
+	/*
+	 * Fast path for unbusy.  If it succeeds, we know that there
+	 * are no waiters, so we do not need a wakeup.
+	 */
+	if (atomic_cmpset_rel_int(&m->busy_lock, VPB_SINGLE_EXCLUSIVER,
+	    VPB_UNBUSIED))
+		return;
+
 	lockacq = !mtx_owned(vm_page_lockptr(m));
 	if (lockacq)
 		vm_page_lock(m);
-	vm_page_flash(m);
-	atomic_store_rel_int(&m->busy_lock, VPB_UNBUSIED);
+	vm_page_xunbusy_locked(m);
 	if (lockacq)
 		vm_page_unlock(m);
 }
@@ -788,8 +807,7 @@ vm_page_xunbusy_hard(vm_page_t m)
 	vm_page_assert_xbusied(m);
 
 	vm_page_lock(m);
-	atomic_store_rel_int(&m->busy_lock, VPB_UNBUSIED);
-	wakeup(m);
+	vm_page_xunbusy_locked(m);
 	vm_page_unlock(m);
 }