From: Andrew Morton <akpm@linux-foundation.org>
To: mm-commits@vger.kernel.org,ziy@nvidia.com,akpm@linux-foundation.org
Subject: + mm-page-flags-check-page-folio-private-instead-of-pg_private.patch added to mm-unstable branch
Date: Sun, 20 Sep 2026 21:09:56 -0700 [thread overview]
Message-ID: <20260921040957.515841F000FF@smtp.kernel.org> (raw)
The patch titled
Subject: mm/page-flags: check page/folio->private instead of PG_private
has been added to the -mm mm-unstable 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-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Zi Yan <ziy@nvidia.com>
Subject: mm/page-flags: check page/folio->private instead of PG_private
Date: Sun, 20 Sep 2026 22:28:06 -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_test_private() and PagePrivate() now read folio/page->private
plainly instead of an atomic read of PG_private bit, so KCSAN complains
about possible data races. Annotate them with data_race().
folio_expected_ref_count() can be called without the folio lock, so
annotate folio->mapping with data_race() while at it.
folio_set/clear_private() and Set/ClearPagePrivate() become no-ops.
PG_private is no longer checked at page free time. They will be removed in
an upcoming commit.
Remove KPF_PRIVATE since PG_private is no longer used.
Assisted-by: LLM
Link: https://lore.kernel.org/20260920-remove-pg_private-v5-10-bb68b6a21869@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 | 19 +++++----
include/linux/page-flags.h | 57 +++++++++++++++++++++++++---
include/trace/events/pagemap.h | 2
mm/huge_memory.c | 2
mm/migrate.c | 2
mm/page-writeback.c | 2
mm/vmscan.c | 2
tools/mm/page-types.c | 2
10 files changed, 68 insertions(+), 22 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 +3044,15 @@ 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.
+ */
+ ref_count += 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
@@ -575,9 +575,31 @@ FOLIO_FLAG(swapbacked, FOLIO_HEAD_PAGE)
/*
* Private page markings that may be used by the filesystem that owns the page
* for its own purposes.
- * - PG_private and PG_private_2 cause release_folio() and co to be invoked
+ * - folio->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)
+{
+ /*
+ * data_race() is added for readers without holding the folio lock.
+ * Only the NULL/non-NULL answer is used and both are valid while
+ * private is being attached or detached, so the race is benign.
+ */
+ return data_race(folio->private);
+}
+
+static __always_inline int PagePrivate(const struct page *page)
+{
+ /* See folio_test_private() for data_race() use */
+ return !!data_race(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 +1191,7 @@ 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 +1215,31 @@ 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.
+ *
+ * Return: true if the folio has private data attached.
+ */
+static inline bool folio_has_attached_private(const struct folio *folio)
+{
+ /*
+ * 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 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 +1249,7 @@ 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 +22,7 @@
(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) \
+ (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
@@ -4846,7 +4846,7 @@ static int split_huge_pages_pid(int pid,
* will try to drop it before split and then check if the folio
* can be split or not. So skip the check here.
*/
- if (!folio_test_private(folio) &&
+ if (!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 +2705,7 @@ bool filemap_dirty_folio(struct address_
if (folio_test_set_dirty(folio))
return false;
- __folio_mark_dirty(folio, mapping, !folio_test_private(folio));
+ __folio_mark_dirty(folio, mapping, !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
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
reply other threads:[~2026-09-21 4:09 UTC|newest]
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