mm: introduce page reference manipulation functions

The success of CMA allocation largely depends on the success of
migration and key factor of it is page reference count.  Until now, page
reference is manipulated by direct calling atomic functions so we cannot
follow up who and where manipulate it.  Then, it is hard to find actual
reason of CMA allocation failure.  CMA allocation should be guaranteed
to succeed so finding offending place is really important.

In this patch, call sites where page reference is manipulated are
converted to introduced wrapper function.  This is preparation step to
add tracepoint to each page reference manipulation function.  With this
facility, we can easily find reason of CMA allocation failure.  There is
no functional change in this patch.

In addition, this patch also converts reference read sites.  It will
help a second step that renames page._count to something else and
prevents later attempt to direct access to it (Suggested by Andrew).

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/net/ethernet/intel/fm10k/fm10k_main.c

@@ -243,7 +243,7 @@ static bool fm10k_can_reuse_rx_page(struct fm10k_rx_buffer *rx_buffer,
 	/* Even if we own the page, we are not allowed to use atomic_set()
 	 * This would break get_page_unless_zero() users.
 	 */
-	atomic_inc(&page->_count);
+	page_ref_inc(page);
 
 	return true;
 }

drivers/net/ethernet/intel/igb/igb_main.c

@@ -6630,7 +6630,7 @@ static bool igb_can_reuse_rx_page(struct igb_rx_buffer *rx_buffer,
 	/* Even if we own the page, we are not allowed to use atomic_set()
 	 * This would break get_page_unless_zero() users.
 	 */
-	atomic_inc(&page->_count);
+	page_ref_inc(page);
 
 	return true;
 }

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -1942,7 +1942,7 @@ static bool ixgbe_add_rx_frag(struct ixgbe_ring *rx_ring,
 	/* Even if we own the page, we are not allowed to use atomic_set()
 	 * This would break get_page_unless_zero() users.
 	 */
-	atomic_inc(&page->_count);
+	page_ref_inc(page);
 
 	return true;
 }

drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c

@@ -837,7 +837,7 @@ add_tail_frag:
 	/* Even if we own the page, we are not allowed to use atomic_set()
 	 * This would break get_page_unless_zero() users.
 	 */
-	atomic_inc(&page->_count);
+	page_ref_inc(page);
 
 	return true;
 }