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>

1 files changed, 85 insertions, 0 deletions

diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
new file mode 100644
index 000000000000..30f5817f6b8e
--- /dev/null
+++ b/include/linux/page_ref.h
@@ -0,0 +1,85 @@
+#ifndef _LINUX_PAGE_REF_H
+#define _LINUX_PAGE_REF_H
+
+#include <linux/atomic.h>
+#include <linux/mm_types.h>
+#include <linux/page-flags.h>
+
+static inline int page_ref_count(struct page *page)
+{
+	return atomic_read(&page->_count);
+}
+
+static inline int page_count(struct page *page)
+{
+	return atomic_read(&compound_head(page)->_count);
+}
+
+static inline void set_page_count(struct page *page, int v)
+{
+	atomic_set(&page->_count, v);
+}
+
+/*
+ * Setup the page count before being freed into the page allocator for
+ * the first time (boot or memory hotplug)
+ */
+static inline void init_page_count(struct page *page)
+{
+	set_page_count(page, 1);
+}
+
+static inline void page_ref_add(struct page *page, int nr)
+{
+	atomic_add(nr, &page->_count);
+}
+
+static inline void page_ref_sub(struct page *page, int nr)
+{
+	atomic_sub(nr, &page->_count);
+}
+
+static inline void page_ref_inc(struct page *page)
+{
+	atomic_inc(&page->_count);
+}
+
+static inline void page_ref_dec(struct page *page)
+{
+	atomic_dec(&page->_count);
+}
+
+static inline int page_ref_sub_and_test(struct page *page, int nr)
+{
+	return atomic_sub_and_test(nr, &page->_count);
+}
+
+static inline int page_ref_dec_and_test(struct page *page)
+{
+	return atomic_dec_and_test(&page->_count);
+}
+
+static inline int page_ref_dec_return(struct page *page)
+{
+	return atomic_dec_return(&page->_count);
+}
+
+static inline int page_ref_add_unless(struct page *page, int nr, int u)
+{
+	return atomic_add_unless(&page->_count, nr, u);
+}
+
+static inline int page_ref_freeze(struct page *page, int count)
+{
+	return likely(atomic_cmpxchg(&page->_count, count, 0) == count);
+}
+
+static inline void page_ref_unfreeze(struct page *page, int count)
+{
+	VM_BUG_ON_PAGE(page_count(page) != 0, page);
+	VM_BUG_ON(count == 0);
+
+	atomic_set(&page->_count, count);
+}
+
+#endif