gfs2: stop using generic_writepages in gfs2_ail1_start_one

Use filemap_fdatawrite_wbc instead of generic_writepages in
gfs2_ail1_start_one so that the functin can also cope with address_space
operations that only implement ->writepages and to properly account
for cgroup writeback.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

fs/gfs2/log.c

@@ -131,7 +131,7 @@ __acquires(&sdp->sd_ail_lock)
 		if (!mapping)
 			continue;
 		spin_unlock(&sdp->sd_ail_lock);
-		ret = generic_writepages(mapping, wbc);
+		ret = filemap_fdatawrite_wbc(mapping, wbc);
 		if (need_resched()) {
 			blk_finish_plug(plug);
 			cond_resched();
@@ -222,8 +222,7 @@ void gfs2_ail1_flush(struct gfs2_sbd *sdp, struct writeback_control *wbc)
 	spin_unlock(&sdp->sd_ail_lock);
 	blk_finish_plug(&plug);
 	if (ret) {
-		gfs2_lm(sdp, "gfs2_ail1_start_one (generic_writepages) "
-			"returned: %d\n", ret);
+		gfs2_lm(sdp, "gfs2_ail1_start_one returned: %d\n", ret);
 		gfs2_withdraw(sdp);
 	}
 	trace_gfs2_ail_flush(sdp, wbc, 0);