linux-kernel - [PATCH 2/3] mm: thp: microoptimize compound

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Date:	Fri,  6 May 2016 17:03:59 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>
Subject: [PATCH 2/3] mm: thp: microoptimize compound_mapcount()

compound_mapcount() is only called after PageCompound() has already
been checked by the caller, so there's no point to check it again. Gcc
may optimize it away too because it's inline but this will remove the
runtime check for sure and add it'll add an assert instead.

Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
---
 include/linux/mm.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 263f229..726ba80 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -471,8 +471,7 @@ static inline atomic_t *compound_mapcount_ptr(struct page *page)
 
 static inline int compound_mapcount(struct page *page)
 {
-	if (!PageCompound(page))
-		return 0;
+	VM_BUG_ON_PAGE(!PageCompound(page), page);
 	page = compound_head(page);
 	return atomic_read(compound_mapcount_ptr(page)) + 1;
 }