[PATCH 8/8] mm: Optimise PagePolicyTailRead

[Matthew Wilcox <willy@infradead.org>]

From: Matthew Wilcox <mawilcox@microsoft.com>

Since we're checking that PageTail isn't true when we're writing to the
bits, we don't need to call compound_head() either.  This saves us four
instructions per invocation of SetPageFoo / ClearPageFoo for those bits
with a TailRead policy.
---
 include/linux/page-flags.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 1960b5e4b9ab..38ed6f4365d2 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -174,8 +174,10 @@ static __always_inline
 struct page *PagePolicyTailRead(struct page *page, bool modify)
 {
 	CheckPageInit(page);
-	VM_BUG_ON_PGFLAGS(modify && PageTail(page), page);
-	return compound_head(page);
+	if (!modify)
+		return compound_head(page);
+	VM_BUG_ON_PGFLAGS(PageTail(page), page);
+	return page;
 }
 
 static __always_inline struct page *PagePolicyNoCompound(struct page *page)
-- 
2.16.3