nfs: Provide and use helper functions for marking a page as unstable

Signed-off-by: Tom Haynes <loghyr@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index 212b8c8..b802fb3 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -598,6 +598,19 @@
 }
 
 /*
+ * Record the page as unstable and mark its inode as dirty.
+ */
+static inline
+void nfs_mark_page_unstable(struct page *page)
+{
+	struct inode *inode = page_file_mapping(page)->host;
+
+	inc_zone_page_state(page, NR_UNSTABLE_NFS);
+	inc_bdi_stat(inode_to_bdi(inode), BDI_RECLAIMABLE);
+	 __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
+}
+
+/*
  * Determine the number of bytes of data the page contains
  */
 static inline