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.

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

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index f56282491a48fd4c36fddbfb9a908e1ca42c7999..a8f7bd8ea1c62983088a7811595a94a66b15c5be 100644 (file)
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -341,9 +341,7 @@ static inline struct page *find_subpage(struct page *head, pgoff_t index)
        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);