Three improvements to vnode_pager_generic_getpages():

Eliminate an exclusive object lock acquisition and release on the expected
execution path.

Do page zeroing before the object lock is acquired rather than during the
time that the object lock is held.

Use vm_pager_free_nonreq() to eliminate duplicated code.

Reviewed by:	kib
MFC after:	6 weeks
Sponsored by:	EMC / Isilon Storage Division

sys/vm/vnode_pager.c

@@ -771,25 +771,25 @@ vnode_pager_generic_getpages(struct vnode *vp, vm_page_t *m, int bytecount,
 		return vnode_pager_input_smlfs(object, m[reqpage]);
 	}
 
+	/*
+	 * Since the caller has busied the requested page, that page's valid
+	 * field will not be changed by other threads.
+	 */
+	vm_page_assert_xbusied(m[reqpage]);
+
 	/*
 	 * If we have a completely valid page available to us, we can
 	 * clean up and return.  Otherwise we have to re-read the
 	 * media.
 	 */
-	VM_OBJECT_WLOCK(object);
 	if (m[reqpage]->valid == VM_PAGE_BITS_ALL) {
-		for (i = 0; i < count; i++)
-			if (i != reqpage) {
-				vm_page_lock(m[i]);
-				vm_page_free(m[i]);
-				vm_page_unlock(m[i]);
-			}
-		VM_OBJECT_WUNLOCK(object);
-		return VM_PAGER_OK;
+		vm_pager_free_nonreq(object, m, reqpage, count);
+		return (VM_PAGER_OK);
 	} else if (reqblock == -1) {
 		pmap_zero_page(m[reqpage]);
 		KASSERT(m[reqpage]->dirty == 0,
 		    ("vnode_pager_generic_getpages: page %p is dirty", m));
+		VM_OBJECT_WLOCK(object);
 		m[reqpage]->valid = VM_PAGE_BITS_ALL;
 		for (i = 0; i < count; i++)
 			if (i != reqpage) {
@@ -799,9 +799,11 @@ vnode_pager_generic_getpages(struct vnode *vp, vm_page_t *m, int bytecount,
 			}
 		VM_OBJECT_WUNLOCK(object);
 		return (VM_PAGER_OK);
+	} else if (m[reqpage]->valid != 0) {
+		VM_OBJECT_WLOCK(object);
+		m[reqpage]->valid = 0;
+		VM_OBJECT_WUNLOCK(object);
 	}
-	m[reqpage]->valid = 0;
-	VM_OBJECT_WUNLOCK(object);
 
 	/*
 	 * here on direct device I/O