diff --git a/mm/truncate.c b/mm/truncate.c
index 29a9b8a..e13f22e 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -304,6 +304,11 @@
  * @lstart: offset from which to truncate
  *
  * Called under (and serialised by) inode->i_mutex.
+ *
+ * Note: When this function returns, there can be a page in the process of
+ * deletion (inside __delete_from_page_cache()) in the specified range.  Thus
+ * mapping->nrpages can be non-zero when this function returns even after
+ * truncation of the whole mapping.
  */
 void truncate_inode_pages(struct address_space *mapping, loff_t lstart)
 {