xfs: simplify xfs_vm_writepage

The writepage implementation in XFS still tries to deal with dirty but
unmapped buffers which used to caused by writes through shared mmaps.  Since
the introduction of ->page_mkwrite these can't happen anymore, so remove the
code dealing with them.

Note that the all_bh variable which causes us to start I/O on all buffers on
the pages was controlled by the count of unmapped buffers, which also
included those not actually dirty.  It's now unconditionally initialized to
0 but set to 1 for the case of small file size extensions.  It probably can
be removed entirely, but that's left for another patch.

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

diff --git a/fs/xfs/linux-2.6/xfs_trace.h b/fs/xfs/linux-2.6/xfs_trace.h
index 0aea6d5..3f2eec2 100644
--- a/fs/xfs/linux-2.6/xfs_trace.h
+++ b/fs/xfs/linux-2.6/xfs_trace.h
@@ -832,33 +832,29 @@
 		__field(loff_t, size)
 		__field(unsigned long, offset)
 		__field(int, delalloc)
-		__field(int, unmapped)
 		__field(int, unwritten)
 	),
 	TP_fast_assign(
-		int delalloc = -1, unmapped = -1, unwritten = -1;
+		int delalloc = -1, unwritten = -1;
 
 		if (page_has_buffers(page))
-			xfs_count_page_state(page, &delalloc,
-					     &unmapped, &unwritten);
+			xfs_count_page_state(page, &delalloc, &unwritten);
 		__entry->dev = inode->i_sb->s_dev;
 		__entry->ino = XFS_I(inode)->i_ino;
 		__entry->pgoff = page_offset(page);
 		__entry->size = i_size_read(inode);
 		__entry->offset = off;
 		__entry->delalloc = delalloc;
-		__entry->unmapped = unmapped;
 		__entry->unwritten = unwritten;
 	),
 	TP_printk("dev %d:%d ino 0x%llx pgoff 0x%lx size 0x%llx offset %lx "
-		  "delalloc %d unmapped %d unwritten %d",
+		  "delalloc %d unwritten %d",
 		  MAJOR(__entry->dev), MINOR(__entry->dev),
 		  __entry->ino,
 		  __entry->pgoff,
 		  __entry->size,
 		  __entry->offset,
 		  __entry->delalloc,
-		  __entry->unmapped,
 		  __entry->unwritten)
 )