[PATCH v3 4/5] alloc_tag: introduce pgalloc_tag_ref to abstract page tag references

[Suren Baghdasaryan <surenb@google.com>]

To simplify later changes to page tag references, introduce new
pgalloc_tag_ref and pgtag_ref_handle types. 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 | 108 ++++++++++++++++++++++++------------
 lib/alloc_tag.c             |   3 +-
 3 files changed, 88 insertions(+), 48 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..bc65710ee1f9 100644
--- a/include/linux/pgalloc_tag.h
+++ b/include/linux/pgalloc_tag.h
@@ -9,48 +9,83 @@
 
 #ifdef CONFIG_MEM_ALLOC_PROFILING
 
+typedef union codetag_ref	pgalloc_tag_ref;
+
+static inline void read_pgref(pgalloc_tag_ref *pgref, union codetag_ref *ref)
+{
+	ref->ct = pgref->ct;
+}
+
+static inline void write_pgref(pgalloc_tag_ref *pgref, union codetag_ref *ref)
+{
+	pgref->ct = ref->ct;
+}
+
+union pgtag_ref_handle {
+	pgalloc_tag_ref *pgref;	/* reference in page extension */
+};
+
 #include <linux/page_ext.h>
 
 extern struct page_ext_operations page_alloc_tagging_ops;
 
-static inline union codetag_ref *codetag_ref_from_page_ext(struct page_ext *page_ext)
+static inline pgalloc_tag_ref *pgref_from_page_ext(struct page_ext *page_ext)
 {
-	return (union codetag_ref *)page_ext_data(page_ext, &page_alloc_tagging_ops);
+	return (pgalloc_tag_ref *)page_ext_data(page_ext, &page_alloc_tagging_ops);
 }
 
-static inline struct page_ext *page_ext_from_codetag_ref(union codetag_ref *ref)
+static inline struct page_ext *page_ext_from_pgref(pgalloc_tag_ref *pgref)
 {
-	return (void *)ref - page_alloc_tagging_ops.offset;
+	return (void *)pgref - 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;
+	pgalloc_tag_ref *pgref;
 
-		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;
+
+	pgref = pgref_from_page_ext(page_ext);
+	read_pgref(pgref, ref);
+	handle->pgref = pgref;
+	return true;
+}
+
+static inline void put_page_tag_ref(union pgtag_ref_handle handle)
+{
+	if (WARN_ON(!handle.pgref))
+		return;
+
+	page_ext_put(page_ext_from_pgref(handle.pgref));
 }
 
-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.pgref || !ref))
 		return;
 
-	page_ext_put(page_ext_from_codetag_ref(ref));
+	write_pgref(handle.pgref, ref);
 }
 
 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 +94,13 @@ 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 +108,13 @@ 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 +124,14 @@ 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 +146,6 @@ 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) {}
diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
index 648f32d52b8d..2ef762acc203 100644
--- a/lib/alloc_tag.c
+++ b/lib/alloc_tag.c
@@ -5,6 +5,7 @@
 #include <linux/gfp.h>
 #include <linux/module.h>
 #include <linux/page_ext.h>
+#include <linux/pgalloc_tag.h>
 #include <linux/proc_fs.h>
 #include <linux/seq_buf.h>
 #include <linux/seq_file.h>
@@ -474,7 +475,7 @@ static __init void init_page_alloc_tagging(void)
 }
 
 struct page_ext_operations page_alloc_tagging_ops = {
-	.size = sizeof(union codetag_ref),
+	.size = sizeof(pgalloc_tag_ref),
 	.need = need_page_alloc_tagging,
 	.init = init_page_alloc_tagging,
 };
-- 
2.47.0.rc1.288.g06298d1525-goog