+ mm-page-flags-check-page-folio-private-instead-of-pg_private.patch added to mm-new branch

+ mm-page-flags-check-page-folio-private-instead-of-pg_private.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/page-flags: check page/folio->private instead of PG_private
has been added to the -mm mm-new branch.  Its filename is
     mm-page-flags-check-page-folio-private-instead-of-pg_private.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page-flags-check-page-folio-private-instead-of-pg_private.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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   a) Consider who else should be cc'ed
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days

------------------------------------------------------
From: Zi Yan <ziy@nvidia.com>
Subject: mm/page-flags: check page/folio->private instead of PG_private
Date: Sun, 13 Sep 2026 22:24:08 -0400

After the changes of the prior commits, page/folio->private != NULL is now
equivalent to checking PG_private.

Stop checking PG_private on pages and folios and use page/folio->private
instead, except swapcache and hugetlb folios, because the former uses a
field (swp_entry_t swap) overlapping with ->private and the latter sets
its flags in ->private.  Exclude swapcache and hugetlb when the code is
meant to check PG_private only.  PG_swapcache and folio->swap.val cannot
be set/clear as a whole, so excluding swapcache with
folio_test_swapcache() is not reliable.  Instead, use
folio_test_swapbacked(), since PG_swapbacked is stable when a folio is
added to/removed from swapcache.  Add a helper,
folio_has_attached_private(), for this check.

folio_expected_ref_count() can be called without folio lock, so annotate
folio_test_private() with data_race() to avoid triggering race condition
checks.  While at it, annotate folio->mapping too.  Add data_race()
annotation for other lockless callers too.

folio_set/clear_private() and Set/ClearPagePrivate() become no-ops. 
PG_private is no longer checked at page free time.

Remove KPF_PRIVATE since PG_private is no longer used.

Assisted-by: LLM
Link: https://lore.kernel.org/20260913-remove-pg_private-v4-10-848550f7574e@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Liam R. Howlett" <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Nico Pache <nico.pache@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Qi Zheng <qi.zheng@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Kairui Song <kasong@tencent.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Wei Xu <weixugc@google.com>
---

 fs/proc/page.c                    |    1 
 include/linux/kernel-page-flags.h |    1 
 include/linux/mm.h                |   20 +++++++-----
 include/linux/page-flags.h        |   46 ++++++++++++++++++++++++----
 include/trace/events/pagemap.h    |    3 +
 mm/huge_memory.c                  |    3 +
 mm/migrate.c                      |    2 -
 mm/page-writeback.c               |    3 +
 mm/vmscan.c                       |    2 -
 tools/mm/page-types.c             |    2 -
 10 files changed, 62 insertions(+), 21 deletions(-)

--- a/fs/proc/page.c~mm-page-flags-check-page-folio-private-instead-of-pg_private
+++ a/fs/proc/page.c
@@ -232,7 +232,6 @@ u64 stable_page_flags(const struct page
 
 	u |= kpf_copy_bit(k, KPF_RESERVED,	PG_reserved);
 	u |= kpf_copy_bit(k, KPF_OWNER_2,	PG_owner_2);
-	u |= kpf_copy_bit(k, KPF_PRIVATE,	PG_private);
 	u |= kpf_copy_bit(k, KPF_PRIVATE_2,	PG_private_2);
 	u |= kpf_copy_bit(k, KPF_OWNER_PRIVATE,	PG_owner_priv_1);
 	u |= kpf_copy_bit(k, KPF_ARCH,		PG_arch_1);
--- a/include/linux/kernel-page-flags.h~mm-page-flags-check-page-folio-private-instead-of-pg_private
+++ a/include/linux/kernel-page-flags.h
@@ -11,7 +11,6 @@
 #define KPF_RESERVED		32
 #define KPF_MLOCKED		33
 #define KPF_OWNER_2		34
-#define KPF_PRIVATE		35
 #define KPF_PRIVATE_2		36
 #define KPF_OWNER_PRIVATE	37
 #define KPF_ARCH		38
--- a/include/linux/mm.h~mm-page-flags-check-page-folio-private-instead-of-pg_private
+++ a/include/linux/mm.h
@@ -3004,9 +3004,9 @@ static inline bool folio_maybe_mapped_sh
  * @folio: the folio
  *
  * Calculate the expected folio refcount, taking references from the pagecache,
- * swapcache, PG_private and page table mappings into account. Useful in
- * combination with folio_ref_count() to detect unexpected references (e.g.,
- * GUP or other temporary references).
+ * swapcache, private data (folio->private != NULL) and page table mappings into
+ * account. Useful in combination with folio_ref_count() to detect unexpected
+ * references (e.g., GUP or other temporary references).
  *
  * Does currently not consider references from the LRU cache. If the folio
  * was isolated from the LRU (which is the case during migration or split),
@@ -3044,10 +3044,16 @@ static inline int folio_expected_ref_cou
 	ref_count += folio_test_swapcache(folio) << order;
 
 	if (!folio_test_anon(folio)) {
-		/* One reference per page from the pagecache. */
-		ref_count += !!folio->mapping << order;
-		/* One reference from PG_private. */
-		ref_count += folio_test_private(folio);
+		/*
+		 * One reference per page from the pagecache.
+		 * Use data_race() since folio might not be locked.
+		 */
+		ref_count += !!data_race(folio->mapping) << order;
+		/*
+		 * One reference from filesystem private data.
+		 * Use data_race() since folio might not be locked.
+		 */
+		ref_count += data_race(folio_has_attached_private(folio));
 	}
 
 	/* One reference per page table mapping. */
--- a/include/linux/page-flags.h~mm-page-flags-check-page-folio-private-instead-of-pg_private
+++ a/include/linux/page-flags.h
@@ -577,7 +577,23 @@ FOLIO_FLAG(swapbacked, FOLIO_HEAD_PAGE)
  * for its own purposes.
  * - PG_private and PG_private_2 cause release_folio() and co to be invoked
  */
-PAGEFLAG(Private, private, PF_ANY)
+
+static __always_inline bool folio_test_private(const struct folio *folio)
+{
+	return folio->private;
+}
+
+static __always_inline int PagePrivate(const struct page *page)
+{
+	return !!page->private;
+}
+
+/* no-ops during transition */
+static __always_inline void folio_set_private(struct folio *folio) { }
+static __always_inline void folio_clear_private(struct folio *folio) { }
+static __always_inline void SetPagePrivate(struct page *page) { }
+static __always_inline void ClearPagePrivate(struct page *page) { }
+
 FOLIO_FLAG(private_2, FOLIO_HEAD_PAGE)
 
 /* owner_2 can be set on tail pages for anon memory */
@@ -1169,7 +1185,7 @@ static __always_inline void __ClearPageA
  */
 #define PAGE_FLAGS_CHECK_AT_FREE				\
 	(1UL << PG_lru		| 1UL << PG_locked	|	\
-	 1UL << PG_private	| 1UL << PG_private_2	|	\
+	 1UL << PG_private_2	|				\
 	 1UL << PG_writeback	| 1UL << PG_reserved	|	\
 	 1UL << PG_active 	|				\
 	 1UL << PG_unevictable	| __PG_MLOCKED | LRU_GEN_MASK)
@@ -1193,8 +1209,28 @@ static __always_inline void __ClearPageA
 	(0xffUL /* order */		| 1UL << PG_has_hwpoisoned |	\
 	 1UL << PG_large_rmappable	| 1UL << PG_partially_mapped)
 
-#define PAGE_FLAGS_PRIVATE				\
-	(1UL << PG_private | 1UL << PG_private_2)
+/**
+ * folio_has_attached_private - check if the folio has private data attached
+ * @folio: The folio to check.
+ *
+ * Use this in code that may encounter swapcache or hugetlb folios but only
+ * wants to detect attached private data. Swapcache stores swp_entry_t in
+ * folio->swap, a union with folio->private, and hugetlb stores its own flags
+ * in folio->private; both are excluded.
+ *
+ * NOTE: For swapcache, folio->swap.val PG_swapcache are not set as a whole,
+ * so folio_test_swapcache() is not reliable to exclude swapcache.
+ * Use folio_test_swapbacked() instead, since it remains set when a folio is
+ * added to/removed from swapcache.
+ *
+ * Return: true if folio->private is set and the folio is neither swapcache
+ * nor hugetlb.
+ */
+static inline bool folio_has_attached_private(const struct folio *folio)
+{
+	return folio_test_private(folio) && !folio_test_swapbacked(folio) &&
+	       !folio_test_hugetlb(folio);
+}
 /**
  * folio_has_private - Determine if folio has private stuff
  * @folio: The folio to be checked
@@ -1204,7 +1240,7 @@ static __always_inline void __ClearPageA
  */
 static inline int folio_has_private(const struct folio *folio)
 {
-	return !!(folio->flags.f & PAGE_FLAGS_PRIVATE);
+	return folio_has_attached_private(folio) || folio_test_private_2(folio);
 }
 
 #undef PF_ANY
--- a/include/trace/events/pagemap.h~mm-page-flags-check-page-folio-private-instead-of-pg_private
+++ a/include/trace/events/pagemap.h
@@ -22,7 +22,8 @@
 	(folio_test_swapcache(folio)	? PAGEMAP_SWAPCACHE  : 0) | \
 	(folio_test_swapbacked(folio)	? PAGEMAP_SWAPBACKED : 0) | \
 	(folio_test_mappedtodisk(folio)	? PAGEMAP_MAPPEDDISK : 0) | \
-	(folio_test_private(folio)	? PAGEMAP_BUFFERS    : 0) \
+	/* data_race() is used to read attached private locklessly */ \
+	(data_race(folio_has_attached_private(folio))	? PAGEMAP_BUFFERS    : 0) \
 	)
 
 TRACE_EVENT(mm_lru_insertion,
--- a/mm/huge_memory.c~mm-page-flags-check-page-folio-private-instead-of-pg_private
+++ a/mm/huge_memory.c
@@ -4845,8 +4845,9 @@ static int split_huge_pages_pid(int pid,
 		 * For folios with private, split_huge_page_to_list_to_order()
 		 * will try to drop it before split and then check if the folio
 		 * can be split or not. So skip the check here.
+		 * data_race() is used to read attached private locklessly.
 		 */
-		if (!folio_test_private(folio) &&
+		if (!data_race(folio_has_attached_private(folio)) &&
 		    folio_expected_ref_count(folio) != folio_ref_count(folio))
 			goto next;
 
--- a/mm/migrate.c~mm-page-flags-check-page-folio-private-instead-of-pg_private
+++ a/mm/migrate.c
@@ -1327,7 +1327,7 @@ static int migrate_folio_unmap(new_folio
 	 * free the metadata, so the page can be freed.
 	 */
 	if (!src->mapping) {
-		if (folio_test_private(src)) {
+		if (folio_has_attached_private(src)) {
 			try_to_free_buffers(src);
 			goto out;
 		}
--- a/mm/page-writeback.c~mm-page-flags-check-page-folio-private-instead-of-pg_private
+++ a/mm/page-writeback.c
@@ -2705,7 +2705,8 @@ bool filemap_dirty_folio(struct address_
 	if (folio_test_set_dirty(folio))
 		return false;
 
-	__folio_mark_dirty(folio, mapping, !folio_test_private(folio));
+	/* data_race() is used to read attached private locklessly */
+	__folio_mark_dirty(folio, mapping, !data_race(folio_has_attached_private(folio)));
 
 	if (mapping->host) {
 		/* !PageAnon && !swapper_space */
--- a/mm/vmscan.c~mm-page-flags-check-page-folio-private-instead-of-pg_private
+++ a/mm/vmscan.c
@@ -1029,7 +1029,7 @@ static void folio_check_dirty_writeback(
 	*writeback = folio_test_writeback(folio);
 
 	/* Verify dirty/writeback state if the filesystem supports it */
-	if (!folio_test_private(folio))
+	if (!folio_has_attached_private(folio))
 		return;
 
 	mapping = folio_mapping(folio);
--- a/tools/mm/page-types.c~mm-page-flags-check-page-folio-private-instead-of-pg_private
+++ a/tools/mm/page-types.c
@@ -73,7 +73,6 @@
 #define KPF_RESERVED		32
 #define KPF_MLOCKED		33
 #define KPF_OWNER_2		34
-#define KPF_PRIVATE		35
 #define KPF_PRIVATE_2		36
 #define KPF_OWNER_PRIVATE	37
 #define KPF_ARCH		38
@@ -131,7 +130,6 @@ static const char * const page_flag_name
 	[KPF_RESERVED]		= "r:reserved",
 	[KPF_MLOCKED]		= "m:mlocked",
 	[KPF_OWNER_2]		= "d:owner_2",
-	[KPF_PRIVATE]		= "P:private",
 	[KPF_PRIVATE_2]		= "p:private_2",
 	[KPF_OWNER_PRIVATE]	= "O:owner_private",
 	[KPF_ARCH]		= "h:arch",
_

Patches currently in -mm which might be from ziy@nvidia.com are

mm-zsmalloc-replace-pg_private-with-pointer-comparison.patch
perf-ring_buffer-stop-using-pg_private-as-aux-page-high-order-marker.patch
xen-grant-table-stop-setting-pg_private-on-pages-for-grant-mapping.patch
fscrypt-stop-setting-pg_private-on-bounce-page.patch
mm-hugetlb-use-direct-assignment-instead-of-folio_change_private.patch
f2fs-stop-using-pg_private.patch
f2fs-convert-the-private-flag-helpers-to-folio-only.patch
erofs-mm-pagemap-add-readahead_folio_last-to-avoid-folio-private.patch
erofs-use-folio_attach-detach_private-instead-of-direct-assignment.patch
mm-page-flags-check-page-folio-private-instead-of-pg_private.patch
treewide-remove-folio_set-clear_private-usage.patch
ceph-replace-pageprivate-with-page_private.patch
md-md-bitmap-replace-pageprivate-with-page_private.patch
buffer-replace-page_buffer-with-page_private-and-delete-it.patch
treewide-remove-pageprivate-and-pg_private-from-comments-and-docs.patch
mm-page-flags-remove-pg_private.patch
usb-gadgetfs-do-not-warn-about-excessively-large-memory-allocations.patch