mm: rename _count, field of the struct page, to _refcount

Many developers 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.

[akpm@linux-foundation.org: fix comments, per Vlastimil]
[akpm@linux-foundation.org: Documentation/vm/transhuge.txt too]
[sfr@canb.auug.org.au: sync ethernet driver changes]
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Sunil Goutham <sgoutham@cavium.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Manish Chopra <manish.chopra@qlogic.com>
Cc: Yuval Mintz <yuval.mintz@qlogic.com>
Cc: Tariq Toukan <tariqt@mellanox.com>
Cc: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 5 deletions

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index c2d75b4fa86c..1fda9c99ef95 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -73,9 +73,9 @@ struct page {
 			unsigned long counters;
 #else
 			/*
-			 * Keep _count separate from slub cmpxchg_double data.
-			 * As the rest of the double word is protected by
-			 * slab_lock but _count is not.
+			 * Keep _refcount separate from slub cmpxchg_double
+			 * data.  As the rest of the double word is protected by
+			 * slab_lock but _refcount is not.
 			 */
 			unsigned counters;
 #endif
@@ -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;