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>

4 files changed, 27 insertions, 23 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 727f7997..1193a54 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -734,7 +734,7 @@ static inline void get_page(struct page *page)
 	page = compound_head(page);
 	/*
 	 * Getting a normal page or the head of a compound page
-	 * requires to already have an elevated page->_count.
+	 * requires to already have an elevated page->_refcount.
 	 */
 	VM_BUG_ON_PAGE(page_ref_count(page) <= 0, page);
 	page_ref_inc(page);
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index c2d75b4..1fda9c9 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;
diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
index e596d5d9..8b5e0a9 100644
--- a/include/linux/page_ref.h
+++ b/include/linux/page_ref.h
@@ -63,17 +63,17 @@ static inline void __page_ref_unfreeze(struct page *page, int v)
 
 static inline int page_ref_count(struct page *page)
 {
-	return atomic_read(&page->_count);
+	return atomic_read(&page->_refcount);
 }
 
 static inline int page_count(struct page *page)
 {
-	return atomic_read(&compound_head(page)->_count);
+	return atomic_read(&compound_head(page)->_refcount);
 }
 
 static inline void set_page_count(struct page *page, int v)
 {
-	atomic_set(&page->_count, v);
+	atomic_set(&page->_refcount, v);
 	if (page_ref_tracepoint_active(__tracepoint_page_ref_set))
 		__page_ref_set(page, v);
 }
@@ -89,35 +89,35 @@ static inline void init_page_count(struct page *page)
 
 static inline void page_ref_add(struct page *page, int nr)
 {
-	atomic_add(nr, &page->_count);
+	atomic_add(nr, &page->_refcount);
 	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
 		__page_ref_mod(page, nr);
 }
 
 static inline void page_ref_sub(struct page *page, int nr)
 {
-	atomic_sub(nr, &page->_count);
+	atomic_sub(nr, &page->_refcount);
 	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
 		__page_ref_mod(page, -nr);
 }
 
 static inline void page_ref_inc(struct page *page)
 {
-	atomic_inc(&page->_count);
+	atomic_inc(&page->_refcount);
 	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
 		__page_ref_mod(page, 1);
 }
 
 static inline void page_ref_dec(struct page *page)
 {
-	atomic_dec(&page->_count);
+	atomic_dec(&page->_refcount);
 	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
 		__page_ref_mod(page, -1);
 }
 
 static inline int page_ref_sub_and_test(struct page *page, int nr)
 {
-	int ret = atomic_sub_and_test(nr, &page->_count);
+	int ret = atomic_sub_and_test(nr, &page->_refcount);
 
 	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_and_test))
 		__page_ref_mod_and_test(page, -nr, ret);
@@ -126,7 +126,7 @@ static inline int page_ref_sub_and_test(struct page *page, int nr)
 
 static inline int page_ref_dec_and_test(struct page *page)
 {
-	int ret = atomic_dec_and_test(&page->_count);
+	int ret = atomic_dec_and_test(&page->_refcount);
 
 	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_and_test))
 		__page_ref_mod_and_test(page, -1, ret);
@@ -135,7 +135,7 @@ static inline int page_ref_dec_and_test(struct page *page)
 
 static inline int page_ref_dec_return(struct page *page)
 {
-	int ret = atomic_dec_return(&page->_count);
+	int ret = atomic_dec_return(&page->_refcount);
 
 	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_and_return))
 		__page_ref_mod_and_return(page, -1, ret);
@@ -144,7 +144,7 @@ static inline int page_ref_dec_return(struct page *page)
 
 static inline int page_ref_add_unless(struct page *page, int nr, int u)
 {
-	int ret = atomic_add_unless(&page->_count, nr, u);
+	int ret = atomic_add_unless(&page->_refcount, nr, u);
 
 	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_unless))
 		__page_ref_mod_unless(page, nr, ret);
@@ -153,7 +153,7 @@ static inline int page_ref_add_unless(struct page *page, int nr, int u)
 
 static inline int page_ref_freeze(struct page *page, int count)
 {
-	int ret = likely(atomic_cmpxchg(&page->_count, count, 0) == count);
+	int ret = likely(atomic_cmpxchg(&page->_refcount, count, 0) == count);
 
 	if (page_ref_tracepoint_active(__tracepoint_page_ref_freeze))
 		__page_ref_freeze(page, count, ret);
@@ -165,7 +165,7 @@ static inline void page_ref_unfreeze(struct page *page, int count)
 	VM_BUG_ON_PAGE(page_count(page) != 0, page);
 	VM_BUG_ON(count == 0);
 
-	atomic_set(&page->_count, count);
+	atomic_set(&page->_refcount, count);
 	if (page_ref_tracepoint_active(__tracepoint_page_ref_unfreeze))
 		__page_ref_unfreeze(page, count);
 }
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 7e1ab15..fe1513f 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -90,12 +90,12 @@ void release_pages(struct page **pages, int nr, bool cold);
 
 /*
  * speculatively take a reference to a page.
- * If the page is free (_count == 0), then _count is untouched, and 0
- * is returned. Otherwise, _count is incremented by 1 and 1 is returned.
+ * If the page is free (_refcount == 0), then _refcount is untouched, and 0
+ * is returned. Otherwise, _refcount is incremented by 1 and 1 is returned.
  *
  * This function must be called inside the same rcu_read_lock() section as has
  * been used to lookup the page in the pagecache radix-tree (or page table):
- * this allows allocators to use a synchronize_rcu() to stabilize _count.
+ * this allows allocators to use a synchronize_rcu() to stabilize _refcount.
  *
  * Unless an RCU grace period has passed, the count of all pages coming out
  * of the allocator must be considered unstable. page_count may return higher
@@ -111,7 +111,7 @@ void release_pages(struct page **pages, int nr, bool cold);
  * 2. conditionally increment refcount
  * 3. check the page is still in pagecache (if no, goto 1)
  *
- * Remove-side that cares about stability of _count (eg. reclaim) has the
+ * Remove-side that cares about stability of _refcount (eg. reclaim) has the
  * following (with tree_lock held for write):
  * A. atomically check refcount is correct and set it to 0 (atomic_cmpxchg)
  * B. remove page from pagecache