linux-kernel - [PATCH 08/75] mm/gup: Remove an assumption of a contiguous memmap

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Message-Id: <20220204195852.1751729-9-willy@infradead.org>
Date:   Fri,  4 Feb 2022 19:57:45 +0000
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     linux-mm@...ck.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        John Hubbard <jhubbard@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        William Kucharski <william.kucharski@...cle.com>
Subject: [PATCH 08/75] 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@...radead.org>
Reviewed-by: Christoph Hellwig <hch@....de>
Reviewed-by: John Hubbard <jhubbard@...dia.com>
Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
Reviewed-by: William Kucharski <william.kucharski@...cle.com>
---
 include/linux/mm.h | 2 ++
 mm/gup.c           | 4 ++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 213cc569b192..e679a7d66200 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -216,8 +216,10 @@ int overcommit_policy_handler(struct ctl_table *, int, void *, size_t *,
 
 #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
 #define nth_page(page,n) pfn_to_page(page_to_pfn((page)) + (n))
+#define page_nth(head, tail)	(page_to_pfn(tail) - page_to_pfn(head))
 #else
 #define nth_page(page,n) ((page) + (n))
+#define page_nth(head, tail)	((tail) - (head))
 #endif
 
 /* to align the pointer to the (next) page boundary */
diff --git a/mm/gup.c b/mm/gup.c
index 29a8021f10a2..fa75b71820a2 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -263,8 +263,8 @@ 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;
-- 
2.34.1