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, 4 insertions, 4 deletions

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 7e1ab155c67c..fe1513ffb7bf 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