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>

5 files changed, 9 insertions, 9 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b49ee126d4d1..f8ac8f582fd8 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3113,7 +3113,7 @@ static void __split_huge_page_tail(struct page *head, int tail,
 	VM_BUG_ON_PAGE(page_ref_count(page_tail) != 0, page_tail);
 
 	/*
-	 * tail_page->_count is zero and not changing from under us. But
+	 * tail_page->_refcount is zero and not changing from under us. But
 	 * get_page_unless_zero() may be running from under us on the
 	 * tail_page. If we used atomic_set() below instead of atomic_inc(), we
 	 * would then run atomic_set() concurrently with
@@ -3340,7 +3340,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 	if (mlocked)
 		lru_add_drain();
 
-	/* Prevent deferred_split_scan() touching ->_count */
+	/* Prevent deferred_split_scan() touching ->_refcount */
 	spin_lock_irqsave(&pgdata->split_queue_lock, flags);
 	count = page_count(head);
 	mapcount = total_mapcount(head);
diff --git a/mm/internal.h b/mm/internal.h
index b79abb6721cf..098a89e3b97c 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -58,7 +58,7 @@ static inline unsigned long ra_submit(struct file_ra_state *ra,
 }
 
 /*
- * Turn a non-refcounted page (->_count == 0) into refcounted with
+ * Turn a non-refcounted page (->_refcount == 0) into refcounted with
  * a count of one.
  */
 static inline void set_page_refcounted(struct page *page)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c1069efcc4d7..4ce57f938b7f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -794,7 +794,7 @@ static inline int free_pages_check(struct page *page)
 	if (unlikely(page->mapping != NULL))
 		bad_reason = "non-NULL mapping";
 	if (unlikely(page_ref_count(page) != 0))
-		bad_reason = "nonzero _count";
+		bad_reason = "nonzero _refcount";
 	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_FREE)) {
 		bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
 		bad_flags = PAGE_FLAGS_CHECK_AT_FREE;
@@ -6864,7 +6864,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
 		 * We can't use page_count without pin a page
 		 * because another CPU can free compound page.
 		 * This check already skips compound tails of THP
-		 * because their page->_count is zero at all time.
+		 * because their page->_refcount is zero at all time.
 		 */
 		if (!page_ref_count(page)) {
 			if (PageBuddy(page))
diff --git a/mm/slub.c b/mm/slub.c
index 8671de2e5b12..cf1faa4d3992 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -329,8 +329,8 @@ static inline void set_page_slub_counters(struct page *page, unsigned long count
 	tmp.counters = counters_new;
 	/*
 	 * page->counters can cover frozen/inuse/objects as well
-	 * as page->_count.  If we assign to ->counters directly
-	 * we run the risk of losing updates to page->_count, so
+	 * as page->_refcount.  If we assign to ->counters directly
+	 * we run the risk of losing updates to page->_refcount, so
 	 * be careful and only assign to the fields we need.
 	 */
 	page->frozen  = tmp.frozen;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 142cb61f4822..d3a02ac3eed7 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -633,7 +633,7 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
 	 *
 	 * Reversing the order of the tests ensures such a situation cannot
 	 * escape unnoticed. The smp_rmb is needed to ensure the page->flags
-	 * load is not satisfied before that of page->_count.
+	 * load is not satisfied before that of page->_refcount.
 	 *
 	 * Note that if SetPageDirty is always performed via set_page_dirty,
 	 * and thus under tree_lock, then this ordering is not required.
@@ -1720,7 +1720,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
  * It is safe to rely on PG_active against the non-LRU pages in here because
  * nobody will play with that bit on a non-LRU page.
  *
- * The downside is that we have to touch page->_count against each page.
+ * The downside is that we have to touch page->_refcount against each page.
  * But we had to alter page->flags anyway.
  */