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, 5 insertions, 5 deletions

diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt
index d9cb65c..fb0e1f2 100644
--- a/Documentation/vm/transhuge.txt
+++ b/Documentation/vm/transhuge.txt
@@ -394,9 +394,9 @@ hugepage natively. Once finished you can drop the page table lock.
 Refcounting on THP is mostly consistent with refcounting on other compound
 pages:
 
-  - get_page()/put_page() and GUP operate in head page's ->_count.
+  - get_page()/put_page() and GUP operate in head page's ->_refcount.
 
-  - ->_count in tail pages is always zero: get_page_unless_zero() never
+  - ->_refcount in tail pages is always zero: get_page_unless_zero() never
     succeed on tail pages.
 
   - map/unmap of the pages with PTE entry increment/decrement ->_mapcount
@@ -426,15 +426,15 @@ requests to split pinned huge page: it expects page count to be equal to
 sum of mapcount of all sub-pages plus one (split_huge_page caller must
 have reference for head page).
 
-split_huge_page uses migration entries to stabilize page->_count and
+split_huge_page uses migration entries to stabilize page->_refcount and
 page->_mapcount.
 
 We safe against physical memory scanners too: the only legitimate way
 scanner can get reference to a page is get_page_unless_zero().
 
-All tail pages has zero ->_count until atomic_add(). It prevent scanner
+All tail pages has zero ->_refcount until atomic_add(). It prevent scanner
 from geting reference to tail page up to the point. After the atomic_add()
-we don't care about ->_count value.  We already known how many references
+we don't care about ->_refcount value.  We already known how many references
 with should uncharge from head page.
 
 For head page get_page_unless_zero() will succeed and we don't mind. It's