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) <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Cc: Aneesh Kumar K.V <[email protected]>
Cc: Pankaj Gupta <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 1 insertions, 3 deletions

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index f56282491a48..a8f7bd8ea1c6 100644
--- 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);