NFS: don't use FLUSH_SYNC on WB_SYNC_NONE COMMIT calls (try #2)

WB_SYNC_NONE is supposed to mean "don't wait on anything". That should
also include not waiting for COMMIT calls to complete.

WB_SYNC_NONE is also implied when wbc->nonblocking and
wbc->for_background are set, so we can replace those checks in
nfs_commit_unstable_pages with a check for WB_SYNC_NONE.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/write.c

@@ -1431,15 +1431,17 @@ static int nfs_commit_unstable_pages(struct inode *inode, struct writeback_contr
 	int flags = FLUSH_SYNC;
 	int ret = 0;
 
-	/* Don't commit yet if this is a non-blocking flush and there are
-	 * lots of outstanding writes for this mapping.
+	if (wbc->sync_mode == WB_SYNC_NONE) {
+		/* Don't commit yet if this is a non-blocking flush and there
+		 * are a lot of outstanding writes for this mapping.
 		 */
-	if (wbc->sync_mode == WB_SYNC_NONE &&
-	    nfsi->ncommit <= (nfsi->npages >> 1))
+		if (nfsi->ncommit <= (nfsi->npages >> 1))
 			goto out_mark_dirty;
 
-	if (wbc->nonblocking || wbc->for_background)
+		/* don't wait for the COMMIT response */
 		flags = 0;
+	}
+
 	ret = nfs_commit_inode(inode, flags);
 	if (ret >= 0) {
 		if (wbc->sync_mode == WB_SYNC_NONE) {