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, 2 insertions, 2 deletions

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))