[PATCH 2/6] mm: Optimise find_subpage for !THP

[Matthew Wilcox <willy@infradead.org>]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

If THP is disabled, find_subpage can become a no-op.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 include/linux/pagemap.h | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index b4ea3a5d00e5..8785f60b05f8 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -333,14 +333,19 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
 			mapping_gfp_mask(mapping));
 }
 
-static inline struct page *find_subpage(struct page *page, pgoff_t offset)
+/*
+ * Given the page we found in the page cache, return the page corresponding
+ * to this offset in the file
+ */
+static inline struct page *find_subpage(struct page *head, pgoff_t offset)
 {
-	if (PageHuge(page))
-		return page;
+	/* HugeTLBfs wants the head page regardless */
+	if (PageHuge(head))
+		return head;
 
-	VM_BUG_ON_PAGE(PageTail(page), page);
+	VM_BUG_ON_PAGE(PageTail(head), head);
 
-	return page + (offset & (compound_nr(page) - 1));
+	return head + (offset & (hpage_nr_pages(head) - 1));
 }
 
 struct page *find_get_entry(struct address_space *mapping, pgoff_t offset);
-- 
2.25.1