linux-kernel - [PATCH 2/2] mm: rename _count, field of the struct page, to

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Date:	Mon, 28 Mar 2016 14:59:08 +0900
From:	js1304@...il.com
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Johannes Berg <johannes@...solutions.net>,
	"David S. Miller" <davem@...emloft.net>,
	Sunil Goutham <sgoutham@...ium.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: [PATCH 2/2] mm: rename _count, field of the struct page, to _refcount

From: Joonsoo Kim <iamjoonsoo.kim@....com>

Many developer already know that field for reference count of
the struct page is _count and atomic type. They would try to handle it
directly and this could break the purpose of page reference count
tracepoint. To prevent direct _count modification, this patch rename it
to _refcount and add warning message on the code. After that, developer
who need to handle reference count will find that field should not be
accessed directly.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
---
 include/linux/mm_types.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 944b2b3..9e8eb5a 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -97,7 +97,11 @@ struct page {
 					};
 					int units;	/* SLOB */
 				};
-				atomic_t _count;		/* Usage count, see below. */
+				/*
+				 * Usage count, *USE WRAPPER FUNCTION*
+				 * when manual accounting. See page_ref.h
+				 */
+				atomic_t _refcount;
 			};
 			unsigned int active;	/* SLAB */
 		};
@@ -248,7 +252,7 @@ struct page_frag_cache {
 	__u32 offset;
 #endif
 	/* we maintain a pagecount bias, so that we dont dirty cache line
-	 * containing page->_count every time we allocate a fragment.
+	 * containing page->_refcount every time we allocate a fragment.
 	 */
 	unsigned int		pagecnt_bias;
 	bool pfmemalloc;
-- 
1.9.1