Avoid an exclusive acquisition of the object lock on the expected execution

path through the NFS clients' getpages functions.

Introduce vm_pager_free_nonreq().  This function can be used to eliminate
code that is duplicated in many getpages functions.  Also, in contrast to
the code that currently appears in those getpages functions,
vm_pager_free_nonreq() avoids acquiring an exclusive object lock in one
case.

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

1 files changed, 9 insertions, 20 deletions

diff --git a/sys/nfsclient/nfs_bio.c b/sys/nfsclient/nfs_bio.c
index 1f07b4696c9c..1a5b15639d18 100644
--- a/sys/nfsclient/nfs_bio.c
+++ b/sys/nfsclient/nfs_bio.c
@@ -123,23 +123,20 @@ nfs_getpages(struct vop_getpages_args *ap)
 	npages = btoc(count);
 
 	/*
+	 * Since the caller has busied the requested page, that page's valid
+	 * field will not be changed by other threads.
+	 */
+	vm_page_assert_xbusied(pages[ap->a_reqpage]);
+
+	/*
 	 * If the requested page is partially valid, just return it and
 	 * allow the pager to zero-out the blanks.  Partially valid pages
 	 * can only occur at the file EOF.
 	 */
-	VM_OBJECT_WLOCK(object);
 	if (pages[ap->a_reqpage]->valid != 0) {
-		for (i = 0; i < npages; ++i) {
-			if (i != ap->a_reqpage) {
-				vm_page_lock(pages[i]);
-				vm_page_free(pages[i]);
-				vm_page_unlock(pages[i]);
-			}
-		}
-		VM_OBJECT_WUNLOCK(object);
-		return (0);
+		vm_pager_free_nonreq(object, pages, ap->a_reqpage, npages);
+		return (VM_PAGER_OK);
 	}
-	VM_OBJECT_WUNLOCK(object);
 
 	/*
 	 * We use only the kva address for the buffer, but this is extremely
@@ -169,15 +166,7 @@ nfs_getpages(struct vop_getpages_args *ap)
 
 	if (error && (uio.uio_resid == count)) {
 		nfs_printf("nfs_getpages: error %d\n", error);
-		VM_OBJECT_WLOCK(object);
-		for (i = 0; i < npages; ++i) {
-			if (i != ap->a_reqpage) {
-				vm_page_lock(pages[i]);
-				vm_page_free(pages[i]);
-				vm_page_unlock(pages[i]);
-			}
-		}
-		VM_OBJECT_WUNLOCK(object);
+		vm_pager_free_nonreq(object, pages, ap->a_reqpage, npages);
 		return (VM_PAGER_ERROR);
 	}