[PATCH v4 5/6] alloc_tag: introduce pgtag_ref_handle to abstract page tag references

[Suren Baghdasaryan <surenb@google.com>]

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.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 include/linux/mm.h          | 25 +++++-----
 include/linux/pgalloc_tag.h | 92 ++++++++++++++++++++++---------------
 2 files changed, 67 insertions(+), 50 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5cd22303fbc0..8efb4a6a1a70 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4180,37 +4180,38 @@ static inline void pgalloc_tag_split(struct folio *folio, int old_order, int new
 		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_nr_pages(new));
-
-	__alloc_tag_ref_set(ref, tag);
-
-	put_page_tag_ref(ref);
+	alloc_tag_sub(&ref, folio_nr_pages(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)
diff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h
index 59a3deb792a8..b13cd3313a88 100644
--- a/include/linux/pgalloc_tag.h
+++ b/include/linux/pgalloc_tag.h
@@ -11,46 +11,59 @@
 
 #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)
+/* Should be called only if mem_alloc_profiling_enabled() */
+static inline bool get_page_tag_ref(struct page *page, union codetag_ref *ref,
+				    union pgtag_ref_handle *handle)
 {
-	return (union codetag_ref *)page_ext_data(page_ext, &page_alloc_tagging_ops);
-}
+	struct page_ext *page_ext;
+	union codetag_ref *tmp;
 
-static inline struct page_ext *page_ext_from_codetag_ref(union codetag_ref *ref)
-{
-	return (void *)ref - page_alloc_tagging_ops.offset;
+	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;
 }
 
-/* Should be called only if mem_alloc_profiling_enabled() */
-static inline union codetag_ref *get_page_tag_ref(struct page *page)
+static inline void put_page_tag_ref(union pgtag_ref_handle handle)
 {
-	if (page) {
-		struct page_ext *page_ext = page_ext_get(page);
+	if (WARN_ON(!handle.ref))
+		return;
 
-		if (page_ext)
-			return codetag_ref_from_page_ext(page_ext);
-	}
-	return NULL;
+	page_ext_put((void *)handle.ref - page_alloc_tagging_ops.offset);
 }
 
-static inline void put_page_tag_ref(union codetag_ref *ref)
+static inline void update_page_tag_ref(union pgtag_ref_handle handle,
+				       union codetag_ref *ref)
 {
-	if (WARN_ON(!ref))
+	if (WARN_ON(!handle.ref || !ref))
 		return;
 
-	page_ext_put(page_ext_from_codetag_ref(ref));
+	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);
 		}
 	}
 }
@@ -59,11 +72,13 @@ static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,
 				   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);
 		}
 	}
 }
@@ -71,11 +86,13 @@ static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,
 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);
 		}
 	}
 }
@@ -85,13 +102,14 @@ static inline struct alloc_tag *pgalloc_tag_get(struct page *page)
 	struct alloc_tag *tag = NULL;
 
 	if (mem_alloc_profiling_enabled()) {
-		union codetag_ref *ref = get_page_tag_ref(page);
-
-		alloc_tag_sub_check(ref);
-		if (ref) {
-			if (ref->ct)
-				tag = ct_to_alloc_tag(ref->ct);
-			put_page_tag_ref(ref);
+		union pgtag_ref_handle handle;
+		union codetag_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);
 		}
 	}
 
@@ -106,8 +124,6 @@ static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr)
 
 #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) {}
-- 
2.47.0.105.g07ac214952-goog