On Tue, Jul 20, 2021 at 01:42:11PM +0300, Mike Rapoport wrote:

quoted

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index f7c165b5991f..bd0e7e91bfd4 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h

@@ -406,6 +406,17 @@ static inline pgoff_t folio_index(struct folio *folio)
         return folio->index;
 }
 
+/**
+ * folio_next_index - Get the index of the next folio.
+ * @folio: The current folio.
+ *
+ * Return: The index of the folio which follows this folio in the file.
+ */

Maybe note that index is in units of pages?

I don't think this is the place to explain that.  Remember, we already
have:

 * @index: Offset within the file, in units of pages.  For anonymous pages,
 *    this is the index from the beginning of the mmap.

and I don't want to explain every term of art in every function
description.  I think if you're reading this, you can follow the
link to the struct folio description and see what an index is.