[patch 019/166] include/linux/pagemap.h: optimise find_subpage for !THP

Andrew Morton
2020-04-07T03:04:34Z

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Subject: include/linux/pagemap.h: optimise find_subpage for !THP

If THP is disabled, find_subpage() can become a no-op by using
hpage_nr_pages() instead of compound_nr(). hpage_nr_pages() embeds a
check for PageTail, so we can drop the check here.

Link: http://lkml.kernel.org/r/20200318140253.6141-5-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

include/linux/pagemap.h | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

--- a/include/linux/pagemap.h~mm-optimise-find_subpage-for-thp
+++ a/include/linux/pagemap.h
@@ -341,9 +341,7 @@ static inline struct page *find_subpage(
if (PageHuge(head))
return head;

- VM_BUG_ON_PAGE(PageTail(head), head);
-
- return head + (index & (compound_nr(head) - 1));
+ return head + (index & (hpage_nr_pages(head) - 1));
}

struct page *find_get_entry(struct address_space *mapping, pgoff_t offset);
_