Re: [PATCH v6 0/9] mm/page_owner: misc cleanups

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 14 Jul 2026 09:50:59 +0800 Ye Liu <ye.liu@linux.dev> wrote:

> This series collects a few cleanups for mm/page_owner.c that have been
> accumulated while reading through the file.  There is no functional
> change -- the goal is to make the code easier to read and maintain.

Thanks, I updated mm.git's mm-unstable branch to this version of the
patchset.

> v6:
>  - Patch 3: drop unnecessary 'extern' from __folio_set_owner_migrate_reason()
>    declaration in page_owner.h; Adjust the indentation; add Reviewed-by from 
>    Lorenzo Stoakes.
>  - Patch 8: clarify commit message wording; add Reviewed-by from Zi Yan and
>    Vlastimil Babka.
>  - Patch 9: rename patch to cover both TOCTOU fixes; also replace
>    page_memcg_check(page) with extracting objcg from the memcg_data snapshot
>    to fix a second TOCTOU issue; add early return for the MEMCG_DATA_OBJEXTS
>    (slab) case.
>  - Link: https://lore.kernel.org/all/20260701061101.344679-1-ye.liu@linux.dev/

Here's how v6 altered mm.git:


 include/linux/hugetlb.h    |    4 ++--
 include/linux/migrate.h    |    6 +++---
 include/linux/page_owner.h |    2 +-
 mm/page_owner.c            |    8 ++++++--
 4 files changed, 12 insertions(+), 8 deletions(-)

--- a/include/linux/hugetlb.h~b
+++ a/include/linux/hugetlb.h
@@ -155,7 +155,7 @@ bool folio_isolate_hugetlb(struct folio
 int get_hwpoison_hugetlb_folio(struct folio *folio, bool *hugetlb, bool unpoison);
 void folio_putback_hugetlb(struct folio *folio);
 void move_hugetlb_state(struct folio *old_folio, struct folio *new_folio,
-			enum migrate_reason reason);
+		enum migrate_reason reason);
 void hugetlb_fix_reserve_counts(struct inode *inode);
 extern struct mutex *hugetlb_fault_mutex_table;
 u32 hugetlb_fault_mutex_hash(struct address_space *mapping, pgoff_t idx);
@@ -425,7 +425,7 @@ static inline void folio_putback_hugetlb
 }
 
 static inline void move_hugetlb_state(struct folio *old_folio,
-					struct folio *new_folio, enum migrate_reason reason)
+		struct folio *new_folio, enum migrate_reason reason)
 {
 }
 
--- a/include/linux/migrate.h~b
+++ a/include/linux/migrate.h
@@ -57,9 +57,9 @@ void putback_movable_pages(struct list_h
 int migrate_folio(struct address_space *mapping, struct folio *dst,
 		struct folio *src, enum migrate_mode mode);
 int migrate_pages(struct list_head *l, new_folio_t new, free_folio_t free,
-		  unsigned long private, enum migrate_mode mode,
-		  enum migrate_reason reason,
-		  unsigned int *ret_succeeded);
+		unsigned long private, enum migrate_mode mode,
+		enum migrate_reason reason,
+		unsigned int *ret_succeeded);
 struct folio *alloc_migration_target(struct folio *src, unsigned long private);
 bool isolate_movable_ops_page(struct page *page, isolate_mode_t mode);
 bool isolate_folio_to_list(struct folio *folio, struct list_head *list);
--- a/include/linux/page_owner.h~b
+++ a/include/linux/page_owner.h
@@ -15,7 +15,7 @@ extern void __set_page_owner(struct page
 extern void __split_page_owner(struct page *page, int old_order,
 			int new_order);
 extern void __folio_copy_owner(struct folio *newfolio, struct folio *old);
-extern void __folio_set_owner_migrate_reason(struct folio *folio, enum migrate_reason reason);
+void __folio_set_owner_migrate_reason(struct folio *folio, enum migrate_reason reason);
 extern void __dump_page_owner(const struct page *page);
 extern void pagetypeinfo_showmixedcount_print(struct seq_file *m,
 					pg_data_t *pgdat, struct zone *zone);
--- a/mm/page_owner.c~b
+++ a/mm/page_owner.c
@@ -540,6 +540,7 @@ static inline int print_page_owner_memcg
 					 struct page *page)
 {
 	unsigned long memcg_data;
+	struct obj_cgroup *objcg;
 	struct mem_cgroup *memcg;
 	bool online;
 	char name[80];
@@ -549,11 +550,14 @@ static inline int print_page_owner_memcg
 	if (!memcg_data || PageTail(page))
 		goto out_unlock;
 
-	if (memcg_data & MEMCG_DATA_OBJEXTS)
+	if (memcg_data & MEMCG_DATA_OBJEXTS) {
 		ret += scnprintf(kbuf + ret, count - ret,
 				"Slab cache page\n");
+		goto out_unlock;
+	}
 
-	memcg = page_memcg_check(page);
+	objcg = (void *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
+	memcg = objcg ? obj_cgroup_memcg(objcg) : NULL;
 	if (!memcg)
 		goto out_unlock;
 
_