xfs: reduce ioend latency

There is no reason to queue up ioends for processing in user context
unless we actually need it.  Just complete ioends that do not convert
unwritten extents or need a size update from the end_io context.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Alex Elder <aelder@sgi.com>

fs/xfs/xfs_aops.c

@@ -149,6 +149,15 @@ xfs_ioend_new_eof(
 	return isize > ip->i_d.di_size ? isize : 0;
 }
 
+/*
+ * Fast and loose check if this write could update the on-disk inode size.
+ */
+static inline bool xfs_ioend_is_append(struct xfs_ioend *ioend)
+{
+	return ioend->io_offset + ioend->io_size >
+		XFS_I(ioend->io_inode)->i_d.di_size;
+}
+
 /*
  * Update on-disk file size now that data has been written to disk.  The
  * current in-memory file size is i_size.  If a write is beyond eof i_new_size
@@ -186,6 +195,9 @@ xfs_setfilesize(
 
 /*
  * Schedule IO completion handling on the final put of an ioend.
+ *
+ * If there is no work to do we might as well call it a day and free the
+ * ioend right now.
  */
 STATIC void
 xfs_finish_ioend(
@@ -194,8 +206,10 @@ xfs_finish_ioend(
 	if (atomic_dec_and_test(&ioend->io_remaining)) {
 		if (ioend->io_type == IO_UNWRITTEN)
 			queue_work(xfsconvertd_workqueue, &ioend->io_work);
-		else
+		else if (xfs_ioend_is_append(ioend))
 			queue_work(xfsdatad_workqueue, &ioend->io_work);
+		else
+			xfs_destroy_ioend(ioend);
 	}
 }