[PATCH v2 4/6] 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/pgalloc_tag.h | 144 +++++++++++++++++++++++-------------
 lib/alloc_tag.c             |   3 +-
 2 files changed, 95 insertions(+), 52 deletions(-)

diff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h
index 244a328dff62..c76b629d0206 100644
--- a/include/linux/pgalloc_tag.h
+++ b/include/linux/pgalloc_tag.h
@@ -9,48 +9,76 @@
 
 #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;
+}
 #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;
 }
 
+typedef pgalloc_tag_ref	*pgtag_ref_handle;
+
 /* Should be called only if mem_alloc_profiling_enabled() */
-static inline union codetag_ref *get_page_tag_ref(struct page *page)
+static inline pgtag_ref_handle get_page_tag_ref(struct page *page, union codetag_ref *ref)
 {
 	if (page) {
 		struct page_ext *page_ext = page_ext_get(page);
 
-		if (page_ext)
-			return codetag_ref_from_page_ext(page_ext);
+		if (page_ext) {
+			pgalloc_tag_ref *pgref = pgref_from_page_ext(page_ext);
+
+			read_pgref(pgref, ref);
+			return pgref;
+		}
 	}
 	return NULL;
 }
 
-static inline void put_page_tag_ref(union codetag_ref *ref)
+static inline void put_page_tag_ref(pgtag_ref_handle pgref)
 {
-	if (WARN_ON(!ref))
+	if (WARN_ON(!pgref))
 		return;
 
-	page_ext_put(page_ext_from_codetag_ref(ref));
+	page_ext_put(page_ext_from_pgref(pgref));
+}
+
+static inline void update_page_tag_ref(pgtag_ref_handle pgref, union codetag_ref *ref)
+{
+	if (WARN_ON(!pgref || !ref))
+		return;
+
+	write_pgref(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);
-
-		if (ref) {
-			set_codetag_empty(ref);
-			put_page_tag_ref(ref);
+		pgtag_ref_handle handle;
+		union codetag_ref ref;
+
+		handle = get_page_tag_ref(page, &ref);
+		if (handle) {
+			set_codetag_empty(&ref);
+			update_page_tag_ref(handle, &ref);
+			put_page_tag_ref(handle);
 		}
 	}
 }
@@ -59,11 +87,14 @@ 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);
-
-		if (ref) {
-			alloc_tag_add(ref, task->alloc_tag, PAGE_SIZE * nr);
-			put_page_tag_ref(ref);
+		pgtag_ref_handle handle;
+		union codetag_ref ref;
+
+		handle = get_page_tag_ref(page, &ref);
+		if (handle) {
+			alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr);
+			update_page_tag_ref(handle, &ref);
+			put_page_tag_ref(handle);
 		}
 	}
 }
@@ -71,53 +102,58 @@ 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);
-
-		if (ref) {
-			alloc_tag_sub(ref, PAGE_SIZE * nr);
-			put_page_tag_ref(ref);
+		pgtag_ref_handle handle;
+		union codetag_ref ref;
+
+		handle = get_page_tag_ref(page, &ref);
+		if (handle) {
+			alloc_tag_sub(&ref, PAGE_SIZE * nr);
+			update_page_tag_ref(handle, &ref);
+			put_page_tag_ref(handle);
 		}
 	}
 }
 
 static inline void pgalloc_tag_split(struct page *page, unsigned int nr)
 {
-	int i;
-	struct page_ext *first_page_ext;
-	struct page_ext *page_ext;
-	union codetag_ref *ref;
+	pgtag_ref_handle first_pgref;
+	union codetag_ref first_ref;
 	struct alloc_tag *tag;
+	int i;
 
 	if (!mem_alloc_profiling_enabled())
 		return;
 
-	first_page_ext = page_ext = page_ext_get(page);
-	if (unlikely(!page_ext))
+	first_pgref = get_page_tag_ref(page, &first_ref);
+	if (unlikely(!first_pgref))
 		return;
 
-	ref = codetag_ref_from_page_ext(page_ext);
-	if (!ref->ct)
+	if (!first_ref.ct)
 		goto out;
 
-	tag = ct_to_alloc_tag(ref->ct);
-	page_ext = page_ext_next(page_ext);
+	tag = ct_to_alloc_tag(first_ref.ct);
 	for (i = 1; i < nr; i++) {
-		/* Set new reference to point to the original tag */
-		ref = codetag_ref_from_page_ext(page_ext);
-		alloc_tag_add_check(ref, tag);
-		if (ref) {
-			ref->ct = &tag->ct;
+		pgtag_ref_handle handle;
+		union codetag_ref ref;
+
+		page++;
+		handle = get_page_tag_ref(page, &ref);
+		if (handle) {
+			/* Set new reference to point to the original tag */
+			alloc_tag_add_check(&ref, tag);
+			ref.ct = &tag->ct;
 			/*
 			 * We need in increment the call counter every time we split a
 			 * large allocation into smaller ones because when we free each
 			 * part the counter will be decremented.
 			 */
 			this_cpu_inc(tag->counters->calls);
+			update_page_tag_ref(handle, &ref);
+			put_page_tag_ref(handle);
 		}
-		page_ext = page_ext_next(page_ext);
 	}
 out:
-	page_ext_put(first_page_ext);
+	put_page_tag_ref(first_pgref);
 }
 
 static inline struct alloc_tag *pgalloc_tag_get(struct page *page)
@@ -125,13 +161,15 @@ 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);
+		pgtag_ref_handle handle;
+		union codetag_ref ref;
+
+		handle = get_page_tag_ref(page, &ref);
+		if (handle) {
+			alloc_tag_sub_check(&ref);
+			if (ref.ct)
+				tag = ct_to_alloc_tag(ref.ct);
+			put_page_tag_ref(handle);
 		}
 	}
 
@@ -146,8 +184,12 @@ 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) {}
+typedef void	*pgtag_ref_handle;
+
+static inline pgtag_ref_handle
+get_page_tag_ref(struct page *page, union codetag_ref *ref) { return NULL; }
+static inline void put_page_tag_ref(pgtag_ref_handle handle) {}
+static inline void update_page_tag_ref(pgtag_ref_handle handle, 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 19ef02a18611..53bd3236d30b 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>
@@ -436,7 +437,7 @@ 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,
 };
-- 
2.46.0.469.g59c65b2a67-goog