v4.19.13 snapshot.
diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
new file mode 100644
index 0000000..14d14be
--- /dev/null
+++ b/include/linux/page_ref.h
@@ -0,0 +1,183 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_PAGE_REF_H
+#define _LINUX_PAGE_REF_H
+
+#include <linux/atomic.h>
+#include <linux/mm_types.h>
+#include <linux/page-flags.h>
+#include <linux/tracepoint-defs.h>
+
+extern struct tracepoint __tracepoint_page_ref_set;
+extern struct tracepoint __tracepoint_page_ref_mod;
+extern struct tracepoint __tracepoint_page_ref_mod_and_test;
+extern struct tracepoint __tracepoint_page_ref_mod_and_return;
+extern struct tracepoint __tracepoint_page_ref_mod_unless;
+extern struct tracepoint __tracepoint_page_ref_freeze;
+extern struct tracepoint __tracepoint_page_ref_unfreeze;
+
+#ifdef CONFIG_DEBUG_PAGE_REF
+
+/*
+ * Ideally we would want to use the trace_<tracepoint>_enabled() helper
+ * functions. But due to include header file issues, that is not
+ * feasible. Instead we have to open code the static key functions.
+ *
+ * See trace_##name##_enabled(void) in include/linux/tracepoint.h
+ */
+#define page_ref_tracepoint_active(t) static_key_false(&(t).key)
+
+extern void __page_ref_set(struct page *page, int v);
+extern void __page_ref_mod(struct page *page, int v);
+extern void __page_ref_mod_and_test(struct page *page, int v, int ret);
+extern void __page_ref_mod_and_return(struct page *page, int v, int ret);
+extern void __page_ref_mod_unless(struct page *page, int v, int u);
+extern void __page_ref_freeze(struct page *page, int v, int ret);
+extern void __page_ref_unfreeze(struct page *page, int v);
+
+#else
+
+#define page_ref_tracepoint_active(t) false
+
+static inline void __page_ref_set(struct page *page, int v)
+{
+}
+static inline void __page_ref_mod(struct page *page, int v)
+{
+}
+static inline void __page_ref_mod_and_test(struct page *page, int v, int ret)
+{
+}
+static inline void __page_ref_mod_and_return(struct page *page, int v, int ret)
+{
+}
+static inline void __page_ref_mod_unless(struct page *page, int v, int u)
+{
+}
+static inline void __page_ref_freeze(struct page *page, int v, int ret)
+{
+}
+static inline void __page_ref_unfreeze(struct page *page, int v)
+{
+}
+
+#endif
+
+static inline int page_ref_count(struct page *page)
+{
+ return atomic_read(&page->_refcount);
+}
+
+static inline int page_count(struct page *page)
+{
+ return atomic_read(&compound_head(page)->_refcount);
+}
+
+static inline void set_page_count(struct page *page, int v)
+{
+ atomic_set(&page->_refcount, v);
+ if (page_ref_tracepoint_active(__tracepoint_page_ref_set))
+ __page_ref_set(page, 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->_refcount);
+ if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
+ __page_ref_mod(page, nr);
+}
+
+static inline void page_ref_sub(struct page *page, int nr)
+{
+ atomic_sub(nr, &page->_refcount);
+ if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
+ __page_ref_mod(page, -nr);
+}
+
+static inline void page_ref_inc(struct page *page)
+{
+ atomic_inc(&page->_refcount);
+ if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
+ __page_ref_mod(page, 1);
+}
+
+static inline void page_ref_dec(struct page *page)
+{
+ atomic_dec(&page->_refcount);
+ if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
+ __page_ref_mod(page, -1);
+}
+
+static inline int page_ref_sub_and_test(struct page *page, int nr)
+{
+ int ret = atomic_sub_and_test(nr, &page->_refcount);
+
+ if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_and_test))
+ __page_ref_mod_and_test(page, -nr, ret);
+ return ret;
+}
+
+static inline int page_ref_inc_return(struct page *page)
+{
+ int ret = atomic_inc_return(&page->_refcount);
+
+ if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_and_return))
+ __page_ref_mod_and_return(page, 1, ret);
+ return ret;
+}
+
+static inline int page_ref_dec_and_test(struct page *page)
+{
+ int ret = atomic_dec_and_test(&page->_refcount);
+
+ if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_and_test))
+ __page_ref_mod_and_test(page, -1, ret);
+ return ret;
+}
+
+static inline int page_ref_dec_return(struct page *page)
+{
+ int ret = atomic_dec_return(&page->_refcount);
+
+ if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_and_return))
+ __page_ref_mod_and_return(page, -1, ret);
+ return ret;
+}
+
+static inline int page_ref_add_unless(struct page *page, int nr, int u)
+{
+ int ret = atomic_add_unless(&page->_refcount, nr, u);
+
+ if (page_ref_tracepoint_active(__tracepoint_page_ref_mod_unless))
+ __page_ref_mod_unless(page, nr, ret);
+ return ret;
+}
+
+static inline int page_ref_freeze(struct page *page, int count)
+{
+ int ret = likely(atomic_cmpxchg(&page->_refcount, count, 0) == count);
+
+ if (page_ref_tracepoint_active(__tracepoint_page_ref_freeze))
+ __page_ref_freeze(page, count, ret);
+ return ret;
+}
+
+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_release(&page->_refcount, count);
+ if (page_ref_tracepoint_active(__tracepoint_page_ref_unfreeze))
+ __page_ref_unfreeze(page, count);
+}
+
+#endif