From ce3ee09b538f7d8c90170bc48d2c81f018c4cf03 Mon Sep 17 00:00:00 2001
From: Alan Cox <alc@FreeBSD.org>
Date: Sun, 14 Aug 2016 22:00:45 +0000
Subject: [PATCH] Eliminate unneeded vm_page_xbusy() and vm_page_xunbusy()
 operations when neither vm_pager_has_page() nor vm_pager_get_pages() is
 called.

Reviewed by:	kib, markj
MFC after:	3 weeks
---
 sys/kern/kern_exec.c | 5 +++--
 sys/kern/uipc_shm.c  | 5 +++--
 sys/vm/vm_glue.c     | 5 +++--
 3 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c
index 3873c5a8f1d9..e573672f9f72 100644
--- a/sys/kern/kern_exec.c
+++ b/sys/kern/kern_exec.c
@@ -984,8 +984,9 @@ exec_map_first_page(imgp)
 #if VM_NRESERVLEVEL > 0
 	vm_object_color(object, 0);
 #endif
-	ma[0] = vm_page_grab(object, 0, VM_ALLOC_NORMAL);
+	ma[0] = vm_page_grab(object, 0, VM_ALLOC_NORMAL | VM_ALLOC_NOBUSY);
 	if (ma[0]->valid != VM_PAGE_BITS_ALL) {
+		vm_page_xbusy(ma[0]);
 		if (!vm_pager_has_page(object, 0, NULL, &after)) {
 			vm_page_lock(ma[0]);
 			vm_page_free(ma[0]);
@@ -1021,10 +1022,10 @@ exec_map_first_page(imgp)
 			VM_OBJECT_WUNLOCK(object);
 			return (EIO);
 		}
+		vm_page_xunbusy(ma[0]);
 		for (i = 1; i < initial_pagein; i++)
 			vm_page_readahead_finish(ma[i]);
 	}
-	vm_page_xunbusy(ma[0]);
 	vm_page_lock(ma[0]);
 	vm_page_hold(ma[0]);
 	vm_page_activate(ma[0]);
diff --git a/sys/kern/uipc_shm.c b/sys/kern/uipc_shm.c
index 1096a168f33a..be922edf0b0b 100644
--- a/sys/kern/uipc_shm.c
+++ b/sys/kern/uipc_shm.c
@@ -182,8 +182,9 @@ uiomove_object_page(vm_object_t obj, size_t len, struct uio *uio)
 	 * lock to page out tobj's pages because tobj is a OBJT_SWAP
 	 * type object.
 	 */
-	m = vm_page_grab(obj, idx, VM_ALLOC_NORMAL);
+	m = vm_page_grab(obj, idx, VM_ALLOC_NORMAL | VM_ALLOC_NOBUSY);
 	if (m->valid != VM_PAGE_BITS_ALL) {
+		vm_page_xbusy(m);
 		if (vm_pager_has_page(obj, idx, NULL, NULL)) {
 			rv = vm_pager_get_pages(obj, &m, 1, NULL, NULL);
 			if (rv != VM_PAGER_OK) {
@@ -198,8 +199,8 @@ uiomove_object_page(vm_object_t obj, size_t len, struct uio *uio)
 			}
 		} else
 			vm_page_zero_invalid(m, TRUE);
+		vm_page_xunbusy(m);
 	}
-	vm_page_xunbusy(m);
 	vm_page_lock(m);
 	vm_page_hold(m);
 	if (m->queue == PQ_NONE) {
diff --git a/sys/vm/vm_glue.c b/sys/vm/vm_glue.c
index 33b997a261f7..60b822e63079 100644
--- a/sys/vm/vm_glue.c
+++ b/sys/vm/vm_glue.c
@@ -236,8 +236,9 @@ vm_imgact_hold_page(vm_object_t object, vm_ooffset_t offset)
 
 	VM_OBJECT_WLOCK(object);
 	pindex = OFF_TO_IDX(offset);
-	m = vm_page_grab(object, pindex, VM_ALLOC_NORMAL);
+	m = vm_page_grab(object, pindex, VM_ALLOC_NORMAL | VM_ALLOC_NOBUSY);
 	if (m->valid != VM_PAGE_BITS_ALL) {
+		vm_page_xbusy(m);
 		rv = vm_pager_get_pages(object, &m, 1, NULL, NULL);
 		if (rv != VM_PAGER_OK) {
 			vm_page_lock(m);
@@ -246,8 +247,8 @@ vm_imgact_hold_page(vm_object_t object, vm_ooffset_t offset)
 			m = NULL;
 			goto out;
 		}
+		vm_page_xunbusy(m);
 	}
-	vm_page_xunbusy(m);
 	vm_page_lock(m);
 	vm_page_hold(m);
 	vm_page_activate(m);