mm/codetag: add pgalloc_tag_copy()

Add pgalloc_tag_copy() to transfer the codetag from the old folio to the
new one during migration.  This makes original allocation sites persist
cross migration rather than lump into the get_new_folio callbacks passed
into migrate_pages(), e.g., compaction_alloc():

  # echo 1 >/proc/sys/vm/compact_memory
  # grep compaction_alloc /proc/allocinfo

Before this patch:
  132968448  32463  mm/compaction.c:1880 func:compaction_alloc

After this patch:
          0      0  mm/compaction.c:1880 func:compaction_alloc

Link: https://lkml.kernel.org/r/20240906042108.1150526-3-yuzhao@google.com
Fixes: dcfe378 ("lib: introduce support for page allocation tagging")
Signed-off-by: Yu Zhao <yuzhao@google.com>
Acked-by: Suren Baghdasaryan <surenb@google.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/alloc_tag.h

@@ -137,7 +137,16 @@ static inline void alloc_tag_sub_check(union codetag_ref *ref) {}
 /* Caller should verify both ref and tag to be valid */
 static inline void __alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag *tag)
 {
+	alloc_tag_add_check(ref, tag);
+	if (!ref || !tag)
+		return;
+
 	ref->ct = &tag->ct;
+}
+
+static inline void alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag *tag)
+{
+	__alloc_tag_ref_set(ref, tag);
 	/*
 	 * We need in increment the call counter every time we have a new
 	 * allocation or when we split a large allocation into smaller ones.
@@ -147,22 +156,9 @@ static inline void __alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag
 	this_cpu_inc(tag->counters->calls);
 }
 
-static inline void alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag *tag)
-{
-	alloc_tag_add_check(ref, tag);
-	if (!ref || !tag)
-		return;
-
-	__alloc_tag_ref_set(ref, tag);
-}
-
 static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes)
 {
-	alloc_tag_add_check(ref, tag);
-	if (!ref || !tag)
-		return;
-
-	__alloc_tag_ref_set(ref, tag);
+	alloc_tag_ref_set(ref, tag);
 	this_cpu_add(tag->counters->bytes, bytes);
 }
 

include/linux/mm.h

@@ -4108,10 +4108,37 @@ static inline void pgalloc_tag_split(struct folio *folio, int old_order, int new
 		}
 	}
 }
+
+static inline void pgalloc_tag_copy(struct folio *new, struct folio *old)
+{
+	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)
+		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);
+}
 #else /* !CONFIG_MEM_ALLOC_PROFILING */
 static inline void pgalloc_tag_split(struct folio *folio, int old_order, int new_order)
 {
 }
+
+static inline void pgalloc_tag_copy(struct folio *new, struct folio *old)
+{
+}
 #endif /* CONFIG_MEM_ALLOC_PROFILING */
 
 #endif /* _LINUX_MM_H */

mm/migrate.c

@@ -743,6 +743,7 @@ void folio_migrate_flags(struct folio *newfolio, struct folio *folio)
 		folio_set_readahead(newfolio);
 
 	folio_copy_owner(newfolio, folio);
+	pgalloc_tag_copy(newfolio, folio);
 
 	mem_cgroup_migrate(folio, newfolio);
 }