mm/gup: Remove an assumption of a contiguous memmap

This assumption needs the inverse of nth_page(), which is temporarily
named page_nth() until it's renamed later in this series.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/mm/gup.c b/mm/gup.c
index d585aa06afb2..ad120f470735 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -261,8 +261,8 @@ static inline struct page *compound_range_next(struct page *start,
 	next = nth_page(start, i);
 	page = compound_head(next);
 	if (PageHead(page))
-		nr = min_t(unsigned int,
-			   page + compound_nr(page) - next, npages - i);
+		nr = min_t(unsigned int, npages - i,
+			   compound_nr(page) - page_nth(page, next));
 
 	*ntails = nr;
 	return page;