diff --git a/mm/filemap.c b/mm/filemap.c
index 126d397..cbc5772 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2463,6 +2463,9 @@
  * (presumably at page->private).  If the release was successful, return `1'.
  * Otherwise return zero.
  *
+ * This may also be called if PG_fscache is set on a page, indicating that the
+ * page is known to the local caching routines.
+ *
  * The @gfp_mask argument specifies whether I/O may be performed to release
  * this page (__GFP_IO), and whether the call may block (__GFP_WAIT & __GFP_FS).
  *