1 files changed, 300 insertions, 0 deletions
diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
new file mode 100644
index 000000000000..544150d1d5fd
--- /dev/null
+++ b/include/linux/page_ref.h
@@ -0,0 +1,300 @@
+/* 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>
+
+DECLARE_TRACEPOINT(page_ref_set);
+DECLARE_TRACEPOINT(page_ref_mod);
+DECLARE_TRACEPOINT(page_ref_mod_and_test);
+DECLARE_TRACEPOINT(page_ref_mod_and_return);
+DECLARE_TRACEPOINT(page_ref_mod_unless);
+DECLARE_TRACEPOINT(page_ref_freeze);
+DECLARE_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) tracepoint_enabled(t)
+
+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(const struct page *page)
+{
+	return atomic_read(&page->_refcount);
+}
+
+/**
+ * folio_ref_count - The reference count on this folio.
+ * @folio: The folio.
+ *
+ * The refcount is usually incremented by calls to folio_get() and
+ * decremented by calls to folio_put().  Some typical users of the
+ * folio refcount:
+ *
+ * - Each reference from a page table
+ * - The page cache
+ * - Filesystem private data
+ * - The LRU list
+ * - Pipes
+ * - Direct IO which references this page in the process address space
+ *
+ * Return: The number of references to this folio.
+ */
+static inline int folio_ref_count(const struct folio *folio)
+{
+	return page_ref_count(&folio->page);
+}
+
+static inline int page_count(const struct page *page)
+{
+	return folio_ref_count(page_folio(page));
+}
+
+static inline void set_page_count(struct page *page, int v)
+{
+	atomic_set(&page->_refcount, v);
+	if (page_ref_tracepoint_active(page_ref_set))
+		__page_ref_set(page, v);
+}
+
+static inline void folio_set_count(struct folio *folio, int v)
+{
+	set_page_count(&folio->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(page_ref_mod))
+		__page_ref_mod(page, nr);
+}
+
+static inline void folio_ref_add(struct folio *folio, int nr)
+{
+	page_ref_add(&folio->page, nr);
+}
+
+static inline void page_ref_sub(struct page *page, int nr)
+{
+	atomic_sub(nr, &page->_refcount);
+	if (page_ref_tracepoint_active(page_ref_mod))
+		__page_ref_mod(page, -nr);
+}
+
+static inline void folio_ref_sub(struct folio *folio, int nr)
+{
+	page_ref_sub(&folio->page, nr);
+}
+
+static inline int folio_ref_sub_return(struct folio *folio, int nr)
+{
+	int ret = atomic_sub_return(nr, &folio->_refcount);
+
+	if (page_ref_tracepoint_active(page_ref_mod_and_return))
+		__page_ref_mod_and_return(&folio->page, -nr, ret);
+	return ret;
+}
+
+static inline void page_ref_inc(struct page *page)
+{
+	atomic_inc(&page->_refcount);
+	if (page_ref_tracepoint_active(page_ref_mod))
+		__page_ref_mod(page, 1);
+}
+
+static inline void folio_ref_inc(struct folio *folio)
+{
+	page_ref_inc(&folio->page);
+}
+
+static inline void page_ref_dec(struct page *page)
+{
+	atomic_dec(&page->_refcount);
+	if (page_ref_tracepoint_active(page_ref_mod))
+		__page_ref_mod(page, -1);
+}
+
+static inline void folio_ref_dec(struct folio *folio)
+{
+	page_ref_dec(&folio->page);
+}
+
+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(page_ref_mod_and_test))
+		__page_ref_mod_and_test(page, -nr, ret);
+	return ret;
+}
+
+static inline int folio_ref_sub_and_test(struct folio *folio, int nr)
+{
+	return page_ref_sub_and_test(&folio->page, nr);
+}
+
+static inline int page_ref_inc_return(struct page *page)
+{
+	int ret = atomic_inc_return(&page->_refcount);
+
+	if (page_ref_tracepoint_active(page_ref_mod_and_return))
+		__page_ref_mod_and_return(page, 1, ret);
+	return ret;
+}
+
+static inline int folio_ref_inc_return(struct folio *folio)
+{
+	return page_ref_inc_return(&folio->page);
+}
+
+static inline int page_ref_dec_and_test(struct page *page)
+{
+	int ret = atomic_dec_and_test(&page->_refcount);
+
+	if (page_ref_tracepoint_active(page_ref_mod_and_test))
+		__page_ref_mod_and_test(page, -1, ret);
+	return ret;
+}
+
+static inline int folio_ref_dec_and_test(struct folio *folio)
+{
+	return page_ref_dec_and_test(&folio->page);
+}
+
+static inline int page_ref_dec_return(struct page *page)
+{
+	int ret = atomic_dec_return(&page->_refcount);
+
+	if (page_ref_tracepoint_active(page_ref_mod_and_return))
+		__page_ref_mod_and_return(page, -1, ret);
+	return ret;
+}
+
+static inline int folio_ref_dec_return(struct folio *folio)
+{
+	return page_ref_dec_return(&folio->page);
+}
+
+static inline bool page_ref_add_unless(struct page *page, int nr, int u)
+{
+	bool ret = false;
+
+	rcu_read_lock();
+	/* avoid writing to the vmemmap area being remapped */
+	if (page_count_writable(page, u))
+		ret = atomic_add_unless(&page->_refcount, nr, u);
+	rcu_read_unlock();
+
+	if (page_ref_tracepoint_active(page_ref_mod_unless))
+		__page_ref_mod_unless(page, nr, ret);
+	return ret;
+}
+
+static inline bool folio_ref_add_unless(struct folio *folio, int nr, int u)
+{
+	return page_ref_add_unless(&folio->page, nr, u);
+}
+
+/**
+ * folio_try_get - Attempt to increase the refcount on a folio.
+ * @folio: The folio.
+ *
+ * If you do not already have a reference to a folio, you can attempt to
+ * get one using this function.  It may fail if, for example, the folio
+ * has been freed since you found a pointer to it, or it is frozen for
+ * the purposes of splitting or migration.
+ *
+ * Return: True if the reference count was successfully incremented.
+ */
+static inline bool folio_try_get(struct folio *folio)
+{
+	return folio_ref_add_unless(folio, 1, 0);
+}
+
+static inline bool folio_ref_try_add(struct folio *folio, int count)
+{
+	return folio_ref_add_unless(folio, count, 0);
+}
+
+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(page_ref_freeze))
+		__page_ref_freeze(page, count, ret);
+	return ret;
+}
+
+static inline int folio_ref_freeze(struct folio *folio, int count)
+{
+	return page_ref_freeze(&folio->page, 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_release(&page->_refcount, count);
+	if (page_ref_tracepoint_active(page_ref_unfreeze))
+		__page_ref_unfreeze(page, count);
+}
+
+static inline void folio_ref_unfreeze(struct folio *folio, int count)
+{
+	page_ref_unfreeze(&folio->page, count);
+}
+#endif