alloc_tag: introduce pgtag_ref_handle to abstract page tag references

To simplify later changes to page tag references, introduce new
pgtag_ref_handle type. This allows easy replacement of page_ext as a
storage of page allocation tags.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Suren Baghdasaryan <[e-mail]>
Reviewed-by: Pasha Tatashin <[e-mail]>
Cc: Ard Biesheuvel <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Borislav Petkov (AMD) <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Daniel Gomez <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: Davidlohr Bueso <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Dennis Zhou <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: John Hubbard <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Joonsoo Kim <[e-mail]>
Cc: Kalesh Singh <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: Kent Overstreet <[e-mail]>
Cc: Liam R. Howlett <[e-mail]>
Cc: Luis Chamberlain <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Mike Rapoport (Microsoft) <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Cc: Paul E. McKenney <[e-mail]>
Cc: Petr Pavlu <[e-mail]>
Cc: Roman Gushchin <[e-mail]>
Cc: Sami Tolvanen <[e-mail]>
Cc: Sourav Panda <[e-mail]>
Cc: Steven Rostedt (Google) <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Thomas Huth <[e-mail]>
Cc: Uladzislau Rezki (Sony) <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: Xiongwei Song <[e-mail]>
Cc: Yu Zhao <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/mm.h

···
 		return;
 
 	for (i = nr_pages; i < (1 << old_order); i += nr_pages) {
-		union codetag_ref *ref = get_page_tag_ref(folio_page(folio, i));
+		union pgtag_ref_handle handle;
+		union codetag_ref ref;
 
-		if (ref) {
+		if (get_page_tag_ref(folio_page(folio, i), &ref, &handle)) {
 			/* Set new reference to point to the original tag */
-			alloc_tag_ref_set(ref, tag);
-			put_page_tag_ref(ref);
+			alloc_tag_ref_set(&ref, tag);
+			update_page_tag_ref(handle, &ref);
+			put_page_tag_ref(handle);
 		}
 	}
 }
 
 static inline void pgalloc_tag_copy(struct folio *new, struct folio *old)
 {
+	union pgtag_ref_handle handle;
+	union codetag_ref ref;
 	struct alloc_tag *tag;
-	union codetag_ref *ref;
 
 	tag = pgalloc_tag_get(&old->page);
 	if (!tag)
 		return;
 
-	ref = get_page_tag_ref(&new->page);
-	if (!ref)
+	if (!get_page_tag_ref(&new->page, &ref, &handle))
 		return;
 
 	/* Clear the old ref to the original allocation tag. */
 	clear_page_tag_ref(&old->page);
 	/* Decrement the counters of the tag on get_new_folio. */
-	alloc_tag_sub(ref, folio_size(new));
-
-	__alloc_tag_ref_set(ref, tag);
-
-	put_page_tag_ref(ref);
+	alloc_tag_sub(&ref, folio_size(new));
+	__alloc_tag_ref_set(&ref, tag);
+	update_page_tag_ref(handle, &ref);
+	put_page_tag_ref(handle);
 }
 #else /* !CONFIG_MEM_ALLOC_PROFILING */
 static inline void pgalloc_tag_split(struct folio *folio, int old_order, int new_order)

include/linux/pgalloc_tag.h

···
 
 #include <linux/page_ext.h>
 
+union pgtag_ref_handle {
+	union codetag_ref *ref;	/* reference in page extension */
+};
+
 extern struct page_ext_operations page_alloc_tagging_ops;
 
-static inline union codetag_ref *codetag_ref_from_page_ext(struct page_ext *page_ext)
-{
-	return (union codetag_ref *)page_ext_data(page_ext, &page_alloc_tagging_ops);
-}
-
-static inline struct page_ext *page_ext_from_codetag_ref(union codetag_ref *ref)
-{
-	return (void *)ref - page_alloc_tagging_ops.offset;
-}
-
 /* Should be called only if mem_alloc_profiling_enabled() */
-static inline union codetag_ref *get_page_tag_ref(struct page *page)
+static inline bool get_page_tag_ref(struct page *page, union codetag_ref *ref,
+				    union pgtag_ref_handle *handle)
 {
-	if (page) {
-		struct page_ext *page_ext = page_ext_get(page);
+	struct page_ext *page_ext;
+	union codetag_ref *tmp;
 
-		if (page_ext)
-			return codetag_ref_from_page_ext(page_ext);
-	}
-	return NULL;
+	if (!page)
+		return false;
+
+	page_ext = page_ext_get(page);
+	if (!page_ext)
+		return false;
+
+	tmp = (union codetag_ref *)page_ext_data(page_ext, &page_alloc_tagging_ops);
+	ref->ct = tmp->ct;
+	handle->ref = tmp;
+	return true;
 }
 
-static inline void put_page_tag_ref(union codetag_ref *ref)
+static inline void put_page_tag_ref(union pgtag_ref_handle handle)
 {
-	if (WARN_ON(!ref))
+	if (WARN_ON(!handle.ref))
 		return;
 
-	page_ext_put(page_ext_from_codetag_ref(ref));
+	page_ext_put((void *)handle.ref - page_alloc_tagging_ops.offset);
+}
+
+static inline void update_page_tag_ref(union pgtag_ref_handle handle,
+				       union codetag_ref *ref)
+{
+	if (WARN_ON(!handle.ref || !ref))
+		return;
+
+	handle.ref->ct = ref->ct;
 }
 
 static inline void clear_page_tag_ref(struct page *page)
 {
 	if (mem_alloc_profiling_enabled()) {
-		union codetag_ref *ref = get_page_tag_ref(page);
+		union pgtag_ref_handle handle;
+		union codetag_ref ref;
 
-		if (ref) {
-			set_codetag_empty(ref);
-			put_page_tag_ref(ref);
+		if (get_page_tag_ref(page, &ref, &handle)) {
+			set_codetag_empty(&ref);
+			update_page_tag_ref(handle, &ref);
+			put_page_tag_ref(handle);
 		}
 	}
 }
···
 				   unsigned int nr)
 {
 	if (mem_alloc_profiling_enabled()) {
-		union codetag_ref *ref = get_page_tag_ref(page);
+		union pgtag_ref_handle handle;
+		union codetag_ref ref;
 
-		if (ref) {
-			alloc_tag_add(ref, task->alloc_tag, PAGE_SIZE * nr);
-			put_page_tag_ref(ref);
+		if (get_page_tag_ref(page, &ref, &handle)) {
+			alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr);
+			update_page_tag_ref(handle, &ref);
+			put_page_tag_ref(handle);
 		}
 	}
 }
···
 static inline void pgalloc_tag_sub(struct page *page, unsigned int nr)
 {
 	if (mem_alloc_profiling_enabled()) {
-		union codetag_ref *ref = get_page_tag_ref(page);
+		union pgtag_ref_handle handle;
+		union codetag_ref ref;
 
-		if (ref) {
-			alloc_tag_sub(ref, PAGE_SIZE * nr);
-			put_page_tag_ref(ref);
+		if (get_page_tag_ref(page, &ref, &handle)) {
+			alloc_tag_sub(&ref, PAGE_SIZE * nr);
+			update_page_tag_ref(handle, &ref);
+			put_page_tag_ref(handle);
 		}
 	}
 }
···
 	struct alloc_tag *tag = NULL;
 
 	if (mem_alloc_profiling_enabled()) {
-		union codetag_ref *ref = get_page_tag_ref(page);
+		union pgtag_ref_handle handle;
+		union codetag_ref ref;
 
-		alloc_tag_sub_check(ref);
-		if (ref) {
-			if (ref->ct)
-				tag = ct_to_alloc_tag(ref->ct);
-			put_page_tag_ref(ref);
+		if (get_page_tag_ref(page, &ref, &handle)) {
+			alloc_tag_sub_check(&ref);
+			if (ref.ct)
+				tag = ct_to_alloc_tag(ref.ct);
+			put_page_tag_ref(handle);
 		}
 	}
 
···
 
 #else /* CONFIG_MEM_ALLOC_PROFILING */
 
-static inline union codetag_ref *get_page_tag_ref(struct page *page) { return NULL; }
-static inline void put_page_tag_ref(union codetag_ref *ref) {}
 static inline void clear_page_tag_ref(struct page *page) {}
 static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,
 				   unsigned int nr) {}