* [PATCH v2 07/14] erofs: mm/pagemap: add readahead_folio_last() to avoid folio->private
2026-08-31 19:25 [PATCH v2 00/14] Remove PG_private by using page/folio->private checks instead Zi Yan
@ 2026-08-31 19:25 ` Zi Yan
2026-08-31 19:25 ` [PATCH v2 09/14] mm/page-flags: check page/folio->private instead of PG_private Zi Yan
` (4 subsequent siblings)
5 siblings, 0 replies; 14+ messages in thread
From: Zi Yan @ 2026-08-31 19:25 UTC (permalink / raw)
To: David Hildenbrand, Matthew Wilcox (Oracle), Andrew Morton,
Muchun Song, Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Baolin Wang,
Nico Pache, Ryan Roberts, Dev Jain, Barry Song, Lance Yang,
Usama Arif, Gregory Price, Ying Huang, Alistair Popple,
Johannes Weiner, Qi Zheng, Shakeel Butt, Kairui Song
Cc: linux-mm, linux-kernel, Zi Yan, Gao Xiang, Chao Yu, Jan Kara,
Yue Hu, Jeffle Xu, Sandeep Dhavale, Hongbo Li, Chunhai Guo,
linux-erofs, linux-fsdevel
erofs needs to traverse readahead folios in reverse order to achieve
maximum performance by
1. reading all folios from readahead_folio();
2. storing the prior folio pointer in folio->private;
3. traverse from the last folio to the first one.
Add readahead_folio_last() to achieve the same function without using
folio->private. __readahead_advance() helper shares readahead_control
adjustment code among __readahead_folio(), readahead_folio_last(), and
__readahead_batch() by checking new private member, _forward, of
readahead_control.
It prepares for a future commit that replaces PG_private checks with
!folio->private checks. After switching the checks, erofs's use of
folio->private without bumping folio refcount can cause unexpected
outcomes, e.g., in filemap_release_folio(), try_to_free_buffers() becomes
reachable.
No functional change intended.
Assisted-by: Claude:claude-opus-4-8
Assisted-by: Codex:gpt-5
Signed-off-by: Zi Yan <ziy@nvidia.com>
To: Gao Xiang <xiang@kernel.org>
To: Chao Yu <chao@kernel.org>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: Yue Hu <zbestahu@gmail.com>
Cc: Jeffle Xu <jefflexu@linux.alibaba.com>
Cc: Sandeep Dhavale <dhavale@google.com>
Cc: Hongbo Li <hongbohbli@tencent.com>
Cc: Chunhai Guo <guochunhai@vivo.com>
Cc: linux-erofs@lists.ozlabs.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-mm@kvack.org
---
fs/erofs/zdata.c | 13 +++---------
include/linux/pagemap.h | 56 ++++++++++++++++++++++++++++++++++++++++++-------
2 files changed, 51 insertions(+), 18 deletions(-)
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index e1e25ca0d1904..78fd7d980e957 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1898,21 +1898,14 @@ static void z_erofs_readahead(struct readahead_control *rac)
struct inode *realinode = erofs_real_inode(sharedinode, &need_iput);
Z_EROFS_DEFINE_FRONTEND(f, realinode, sharedinode, readahead_pos(rac));
unsigned int nrpages = readahead_count(rac);
- struct folio *head = NULL, *folio;
+ struct folio *folio;
int err;
trace_erofs_readahead(realinode, readahead_index(rac), nrpages, false);
z_erofs_pcluster_readmore(&f, rac, true);
- while ((folio = readahead_folio(rac))) {
- folio->private = head;
- head = folio;
- }
-
- /* traverse in reverse order for best metadata I/O performance */
- while (head) {
- folio = head;
- head = folio_get_private(folio);
+ /* traverse from last to first for best metadata I/O performance */
+ while ((folio = readahead_folio_last(rac))) {
err = z_erofs_scan_folio(&f, folio, true);
if (err && err != -EINTR)
erofs_err(realinode->i_sb, "readahead error at folio %lu @ nid %llu",
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 0adfa6605653d..546e987d5cda7 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1416,6 +1416,7 @@ struct readahead_control {
bool dropbehind;
bool _workingset;
unsigned long _pflags;
+ bool _forward;
};
#define DEFINE_READAHEAD(ractl, f, r, m, i) \
@@ -1480,18 +1481,25 @@ void page_cache_async_readahead(struct address_space *mapping,
page_cache_async_ra(&ractl, folio, req_count);
}
+static inline void __readahead_advance(struct readahead_control *rac)
+{
+ if (rac->_forward)
+ rac->_index += rac->_batch_count;
+
+ rac->_nr_pages -= rac->_batch_count;
+ rac->_batch_count = 0;
+}
+
static inline struct folio *__readahead_folio(struct readahead_control *ractl)
{
struct folio *folio;
BUG_ON(ractl->_batch_count > ractl->_nr_pages);
- ractl->_nr_pages -= ractl->_batch_count;
- ractl->_index += ractl->_batch_count;
+ __readahead_advance(ractl);
+ ractl->_forward = true;
- if (!ractl->_nr_pages) {
- ractl->_batch_count = 0;
+ if (!ractl->_nr_pages)
return NULL;
- }
folio = xa_load(&ractl->mapping->i_pages, ractl->_index);
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
@@ -1517,6 +1525,39 @@ static inline struct folio *readahead_folio(struct readahead_control *ractl)
return folio;
}
+/**
+ * readahead_folio_last - Get the next folio to read, from the tail.
+ * @ractl: The current readahead request.
+ *
+ * Like readahead_folio(), but walks the range back-to-front. The folio is
+ * returned locked with its refcount dropped; the caller unlocks it once I/O
+ * completes. Compound folios are returned once, at their head index.
+ *
+ * Context: The folio is locked.
+ * Return: A pointer to the next folio, or %NULL when done.
+ */
+static inline struct folio *readahead_folio_last(struct readahead_control *ractl)
+{
+ struct folio *folio;
+
+ /* Drop the previously returned batch from the remaining range. */
+ __readahead_advance(ractl);
+ ractl->_forward = false;
+
+ if (!ractl->_nr_pages)
+ return NULL;
+
+ /* xa_load() follows sibling entries, so a tail index returns the head */
+ folio = xa_load(&ractl->mapping->i_pages,
+ ractl->_index + ractl->_nr_pages - 1);
+ VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
+
+ ractl->_batch_count = folio_nr_pages(folio);
+
+ folio_put(folio);
+ return folio;
+}
+
static inline unsigned int __readahead_batch(struct readahead_control *rac,
struct page **array, unsigned int array_sz)
{
@@ -1525,9 +1566,8 @@ static inline unsigned int __readahead_batch(struct readahead_control *rac,
struct folio *folio;
BUG_ON(rac->_batch_count > rac->_nr_pages);
- rac->_nr_pages -= rac->_batch_count;
- rac->_index += rac->_batch_count;
- rac->_batch_count = 0;
+ __readahead_advance(rac);
+ rac->_forward = true;
xas_set(&xas, rac->_index);
rcu_read_lock();
--
2.53.0
^ permalink raw reply related [flat|nested] 14+ messages in thread* [PATCH v2 09/14] mm/page-flags: check page/folio->private instead of PG_private
2026-08-31 19:25 [PATCH v2 00/14] Remove PG_private by using page/folio->private checks instead Zi Yan
2026-08-31 19:25 ` [PATCH v2 07/14] erofs: mm/pagemap: add readahead_folio_last() to avoid folio->private Zi Yan
@ 2026-08-31 19:25 ` Zi Yan
2026-09-01 2:11 ` Zi Yan
2026-08-31 19:25 ` [PATCH v2 10/14] mm/page-flags: introduce folio_test_fs_private() Zi Yan
` (3 subsequent siblings)
5 siblings, 1 reply; 14+ messages in thread
From: Zi Yan @ 2026-08-31 19:25 UTC (permalink / raw)
To: David Hildenbrand, Matthew Wilcox (Oracle), Andrew Morton,
Muchun Song, Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Baolin Wang,
Nico Pache, Ryan Roberts, Dev Jain, Barry Song, Lance Yang,
Usama Arif, Gregory Price, Ying Huang, Alistair Popple,
Johannes Weiner, Qi Zheng, Shakeel Butt, Kairui Song
Cc: linux-mm, linux-kernel, Zi Yan, Steven Rostedt, Masami Hiramatsu,
Jan Kara, Mathieu Desnoyers, Matthew Brost, Joshua Hahn,
Rakie Kim, Byungchul Park, Axel Rasmussen, Yuanchu Xie, Wei Xu,
linux-fsdevel, linux-trace-kernel
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.
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.
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: Claude:claude-opus-4-8
Assisted-by: Codex:gpt-5
Signed-off-by: Zi Yan <ziy@nvidia.com>
To: Andrew Morton <akpm@linux-foundation.org>
To: David Hildenbrand <david@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
To: Lorenzo Stoakes <ljs@kernel.org>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
To: Jan Kara <jack@suse.cz>
To: 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: Zi Yan <ziy@nvidia.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>
Cc: linux-kernel@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-trace-kernel@vger.kernel.org
---
fs/proc/page.c | 1 -
include/linux/kernel-page-flags.h | 1 -
include/linux/mm.h | 22 +++++++++++++++-------
include/linux/page-flags.h | 26 +++++++++++++++++++++-----
include/trace/events/pagemap.h | 4 +++-
mm/huge_memory.c | 4 +++-
mm/migrate.c | 3 ++-
mm/page-writeback.c | 5 ++++-
mm/vmscan.c | 3 ++-
tools/mm/page-types.c | 2 --
10 files changed, 50 insertions(+), 21 deletions(-)
diff --git a/fs/proc/page.c b/fs/proc/page.c
index 260772b20bd99..f90e1030825e9 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -232,7 +232,6 @@ u64 stable_page_flags(const struct page *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);
diff --git a/include/linux/kernel-page-flags.h b/include/linux/kernel-page-flags.h
index 196778a087c4d..fe5ab6e50bd70 100644
--- a/include/linux/kernel-page-flags.h
+++ b/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
diff --git a/include/linux/mm.h b/include/linux/mm.h
index dd09c438fa23e..786f8a47cea6d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3022,9 +3022,9 @@ static inline bool folio_maybe_mapped_shared(struct folio *folio)
* @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),
@@ -3062,10 +3062,18 @@ static inline int folio_expected_ref_count(const struct folio *folio)
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_test_private(folio)) &&
+ !folio_test_hugetlb(folio) &&
+ !folio_test_swapcache(folio);
}
/* One reference per page table mapping. */
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 7a863572adce7..ee7abb3000c11 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -578,7 +578,23 @@ 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 */
@@ -1170,7 +1186,7 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page)
*/
#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)
@@ -1194,8 +1210,6 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page)
(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_private - Determine if folio has private stuff
* @folio: The folio to be checked
@@ -1205,7 +1219,9 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page)
*/
static inline int folio_has_private(const struct folio *folio)
{
- return !!(folio->flags.f & PAGE_FLAGS_PRIVATE);
+ return (!!folio->private && !folio_test_swapcache(folio) &&
+ !folio_test_hugetlb(folio)) ||
+ folio_test_private_2(folio);
}
#undef PF_ANY
diff --git a/include/trace/events/pagemap.h b/include/trace/events/pagemap.h
index 36c3a90f0acca..fb9abec40ec79 100644
--- a/include/trace/events/pagemap.h
+++ b/include/trace/events/pagemap.h
@@ -22,7 +22,9 @@
(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_test_private(folio) && \
+ !folio_test_swapcache(folio) && \
+ !folio_test_hugetlb(folio) ? PAGEMAP_BUFFERS : 0) \
)
TRACE_EVENT(mm_lru_insertion,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ced400f72d43a..546b37ccce37f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -4810,7 +4810,9 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
* 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_test_private(folio) &&
+ !folio_test_swapcache(folio) &&
+ !folio_test_hugetlb(folio)) &&
folio_expected_ref_count(folio) != folio_ref_count(folio))
goto next;
diff --git a/mm/migrate.c b/mm/migrate.c
index 15b45832bcfa7..f14e7bfee14bd 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1327,7 +1327,8 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
* free the metadata, so the page can be freed.
*/
if (!src->mapping) {
- if (folio_test_private(src)) {
+ if (folio_test_private(src) && !folio_test_swapcache(src) &&
+ !folio_test_hugetlb(src)) {
try_to_free_buffers(src);
goto out;
}
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index eeab25d6ce364..4022d6c381896 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2705,7 +2705,10 @@ bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio)
if (folio_test_set_dirty(folio))
return false;
- __folio_mark_dirty(folio, mapping, !folio_test_private(folio));
+ __folio_mark_dirty(folio, mapping,
+ !(folio_test_private(folio) &&
+ !folio_test_swapcache(folio) &&
+ !folio_test_hugetlb(folio)));
if (mapping->host) {
/* !PageAnon && !swapper_space */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index f11491ee9ed5c..ac275eec086b9 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -955,7 +955,8 @@ static void folio_check_dirty_writeback(struct folio *folio,
*writeback = folio_test_writeback(folio);
/* Verify dirty/writeback state if the filesystem supports it */
- if (!folio_test_private(folio))
+ if (!(folio_test_private(folio) && !folio_test_swapcache(folio) &&
+ !folio_test_hugetlb(folio)))
return;
mapping = folio_mapping(folio);
diff --git a/tools/mm/page-types.c b/tools/mm/page-types.c
index 7fc5a8be5997f..47e4781c5fc38 100644
--- a/tools/mm/page-types.c
+++ b/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_names[] = {
[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",
--
2.53.0
^ permalink raw reply related [flat|nested] 14+ messages in thread* Re: [PATCH v2 09/14] mm/page-flags: check page/folio->private instead of PG_private
2026-08-31 19:25 ` [PATCH v2 09/14] mm/page-flags: check page/folio->private instead of PG_private Zi Yan
@ 2026-09-01 2:11 ` Zi Yan
0 siblings, 0 replies; 14+ messages in thread
From: Zi Yan @ 2026-09-01 2:11 UTC (permalink / raw)
To: David Hildenbrand, Matthew Wilcox (Oracle), Andrew Morton,
Muchun Song, Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Baolin Wang,
Nico Pache, Ryan Roberts, Dev Jain, Barry Song, Lance Yang,
Usama Arif, Gregory Price, Ying Huang, Alistair Popple,
Johannes Weiner, Qi Zheng, Shakeel Butt, Kairui Song
Cc: linux-mm, linux-kernel, Zi Yan, Steven Rostedt, Masami Hiramatsu,
Jan Kara, Mathieu Desnoyers, Matthew Brost, Joshua Hahn,
Rakie Kim, Byungchul Park, Axel Rasmussen, Yuanchu Xie, Wei Xu,
linux-fsdevel, linux-trace-kernel
On Mon Aug 31, 2026 at 3:25 PM EDT, Zi Yan wrote:
> 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.
>
> 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.
>
> 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.
>
<snip>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index dd09c438fa23e..786f8a47cea6d 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3022,9 +3022,9 @@ static inline bool folio_maybe_mapped_shared(struct folio *folio)
> * @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),
> @@ -3062,10 +3062,18 @@ static inline int folio_expected_ref_count(const struct folio *folio)
> 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_test_private(folio)) &&
> + !folio_test_hugetlb(folio) &&
> + !folio_test_swapcache(folio);
Sashiko said [Severity: High]:
Could this lockless evaluation of folio->private and PG_swapcache lead to a
TOCTOU race for shmem folios during swap cache removal?
During __delete_from_swap_cache, folio->swap.val (which aliases
folio->private) is cleared before PG_swapcache. Without memory barriers, a
lockless reader like memfd_tag_pins calling folio_expected_ref_count could
observe the stale non-zero folio->private and the newly cleared PG_swapcache.
This would evaluate the condition above as true, falsely inflating the
expected refcount by 1. If the folio has exactly one extra GUP pin, the
inflated expected refcount would match the actual refcount, bypassing the
F_SEAL_WRITE protections.
Answer:
Yes, it is a problem, since folio->swap.val and PG_swapcache cannot be
read as a whole, when __swap_cache_do_del_folio() (was
__delete_from_swap_cache()) clears folio->swap.val first then
PG_swapcache.
Fortunately, PG_swapbacked is stable during the process. So the code can
exclude swapcache folios by checking PG_swapbacked instead.
In the next patch, folio_test_fs_private() will be changed to replace the
new check: folio_test_private() && !folio_test_hugetlb(folio) &&
!folio_test_swapbacked().
<snip>
> diff --git a/include/trace/events/pagemap.h b/include/trace/events/pagemap.h
> index 36c3a90f0acca..fb9abec40ec79 100644
> --- a/include/trace/events/pagemap.h
> +++ b/include/trace/events/pagemap.h
> @@ -22,7 +22,9 @@
> (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_test_private(folio) && \
> + !folio_test_swapcache(folio) && \
> + !folio_test_hugetlb(folio) ? PAGEMAP_BUFFERS : 0) \
Sashiko said:
hould this lockless read of folio->private be annotated with data_race() or
READ_ONCE()?
Since tracepoints like TRACE_EVENT(mm_lru_insertion) are often executed
without the folio lock, concurrent modifications to folio->private could
trigger KCSAN data race warnings here.
Answer:
Yes, will annotate with data_race() here.
> )
>
> TRACE_EVENT(mm_lru_insertion,
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index ced400f72d43a..546b37ccce37f 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -4810,7 +4810,9 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
> * 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_test_private(folio) &&
> + !folio_test_swapcache(folio) &&
> + !folio_test_hugetlb(folio)) &&
> folio_expected_ref_count(folio) != folio_ref_count(folio))
> goto next;
This is another lockless check and data_race() annotation is needed.
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 15b45832bcfa7..f14e7bfee14bd 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1327,7 +1327,8 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
> * free the metadata, so the page can be freed.
> */
> if (!src->mapping) {
> - if (folio_test_private(src)) {
> + if (folio_test_private(src) && !folio_test_swapcache(src) &&
> + !folio_test_hugetlb(src)) {
> try_to_free_buffers(src);
> goto out;
> }
Sashiko said [Severity: High]:
This is a pre-existing issue, but does this generic migration code blindly
assume all private data on an orphaned folio corresponds to buffer heads?
If a folio is orphaned after truncation (src->mapping is NULL) but retains
private data because an earlier release failed, try_to_free_buffers is
unconditionally called. For filesystems like iomap, folio->private contains
custom structures (like iomap_folio_state), not a linked list of buffer
heads. Calling try_to_free_buffers here could lead to type confusion and a
kernel panic when accessing what it expects to be bh->b_this_page.
Answer:
Not an issue. With the help of gpt-5.6-sol, this issue only affects
buffer heads. Folios using iomap always clears folio->private before
folio->mapping is cleared.
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index eeab25d6ce364..4022d6c381896 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2705,7 +2705,10 @@ bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio)
> if (folio_test_set_dirty(folio))
> return false;
>
> - __folio_mark_dirty(folio, mapping, !folio_test_private(folio));
> + __folio_mark_dirty(folio, mapping,
> + !(folio_test_private(folio) &&
> + !folio_test_swapcache(folio) &&
> + !folio_test_hugetlb(folio)));
>
Another place needs data_race() annotation since filemap_dirty_folio()
can be called locklessly (e.g., zap_pte_range()).
--
Best Regards,
Yan, Zi
^ permalink raw reply [flat|nested] 14+ messages in thread
* [PATCH v2 10/14] mm/page-flags: introduce folio_test_fs_private()
2026-08-31 19:25 [PATCH v2 00/14] Remove PG_private by using page/folio->private checks instead Zi Yan
2026-08-31 19:25 ` [PATCH v2 07/14] erofs: mm/pagemap: add readahead_folio_last() to avoid folio->private Zi Yan
2026-08-31 19:25 ` [PATCH v2 09/14] mm/page-flags: check page/folio->private instead of PG_private Zi Yan
@ 2026-08-31 19:25 ` Zi Yan
2026-08-31 19:25 ` [PATCH v2 11/14] treewide: remove folio_set/clear_private() Zi Yan
` (2 subsequent siblings)
5 siblings, 0 replies; 14+ messages in thread
From: Zi Yan @ 2026-08-31 19:25 UTC (permalink / raw)
To: David Hildenbrand, Matthew Wilcox (Oracle), Andrew Morton,
Muchun Song, Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Baolin Wang,
Nico Pache, Ryan Roberts, Dev Jain, Barry Song, Lance Yang,
Usama Arif, Gregory Price, Ying Huang, Alistair Popple,
Johannes Weiner, Qi Zheng, Shakeel Butt, Kairui Song
Cc: linux-mm, linux-kernel, Zi Yan, Steven Rostedt, Masami Hiramatsu,
Mathieu Desnoyers, Matthew Brost, Joshua Hahn, Rakie Kim,
Byungchul Park, linux-fsdevel, linux-trace-kernel
folio_test_fs_private() wraps folio->private != NULL check and excludes
swapcache and hugetlb folios, since swapcache uses swp_entry_t overlapping
with folio->private and hugetlb sets its own flags in folio->private.
Replace open code with the helper, since core MM does this check
frequently.
No functional change intended.
Assisted-by: Claude:claude-opus-4-8
Assisted-by: Codex:gpt-5
Signed-off-by: Zi Yan <ziy@nvidia.com>
To: Andrew Morton <akpm@linux-foundation.org>
To: David Hildenbrand <david@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
To: Lorenzo Stoakes <ljs@kernel.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: Zi Yan <ziy@nvidia.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: linux-kernel@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-trace-kernel@vger.kernel.org
---
include/linux/mm.h | 4 +---
include/linux/page-flags.h | 21 ++++++++++++++++++---
include/trace/events/pagemap.h | 4 +---
mm/huge_memory.c | 4 +---
mm/migrate.c | 3 +--
mm/page-writeback.c | 5 +----
mm/vmscan.c | 3 +--
7 files changed, 24 insertions(+), 20 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 786f8a47cea6d..b5b60f3ad58dc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3071,9 +3071,7 @@ static inline int folio_expected_ref_count(const struct folio *folio)
* One reference from filesystem private data.
* Use data_race() since folio might not be locked.
*/
- ref_count += data_race(folio_test_private(folio)) &&
- !folio_test_hugetlb(folio) &&
- !folio_test_swapcache(folio);
+ ref_count += data_race(folio_test_fs_private(folio));
}
/* One reference per page table mapping. */
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index ee7abb3000c11..9b585e68127a2 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -1210,6 +1210,23 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page)
(0xffUL /* order */ | 1UL << PG_has_hwpoisoned | \
1UL << PG_large_rmappable | 1UL << PG_partially_mapped)
+/**
+ * folio_test_fs_private - check if the folio has filesystem private data
+ * @folio: The folio to check.
+ *
+ * Use this in code that may encounter swapcache or hugetlb folios but only
+ * wants to detect filesystem 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.
+ *
+ * Return: true if folio->private is set and the folio is neither swapcache
+ * nor hugetlb.
+ */
+static inline bool folio_test_fs_private(const struct folio *folio)
+{
+ return folio_test_private(folio) && !folio_test_swapcache(folio) &&
+ !folio_test_hugetlb(folio);
+}
/**
* folio_has_private - Determine if folio has private stuff
* @folio: The folio to be checked
@@ -1219,9 +1236,7 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page)
*/
static inline int folio_has_private(const struct folio *folio)
{
- return (!!folio->private && !folio_test_swapcache(folio) &&
- !folio_test_hugetlb(folio)) ||
- folio_test_private_2(folio);
+ return folio_test_fs_private(folio) || folio_test_private_2(folio);
}
#undef PF_ANY
diff --git a/include/trace/events/pagemap.h b/include/trace/events/pagemap.h
index fb9abec40ec79..5425ef7bbae6e 100644
--- a/include/trace/events/pagemap.h
+++ b/include/trace/events/pagemap.h
@@ -22,9 +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) && \
- !folio_test_swapcache(folio) && \
- !folio_test_hugetlb(folio) ? PAGEMAP_BUFFERS : 0) \
+ (folio_test_fs_private(folio) ? PAGEMAP_BUFFERS : 0) \
)
TRACE_EVENT(mm_lru_insertion,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 546b37ccce37f..d085fd09466ef 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -4810,9 +4810,7 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
* 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) &&
- !folio_test_swapcache(folio) &&
- !folio_test_hugetlb(folio)) &&
+ if (!folio_test_fs_private(folio) &&
folio_expected_ref_count(folio) != folio_ref_count(folio))
goto next;
diff --git a/mm/migrate.c b/mm/migrate.c
index f14e7bfee14bd..666a7365e16e8 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1327,8 +1327,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
* free the metadata, so the page can be freed.
*/
if (!src->mapping) {
- if (folio_test_private(src) && !folio_test_swapcache(src) &&
- !folio_test_hugetlb(src)) {
+ if (folio_test_fs_private(src)) {
try_to_free_buffers(src);
goto out;
}
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 4022d6c381896..e03a1c46bce01 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2705,10 +2705,7 @@ bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio)
if (folio_test_set_dirty(folio))
return false;
- __folio_mark_dirty(folio, mapping,
- !(folio_test_private(folio) &&
- !folio_test_swapcache(folio) &&
- !folio_test_hugetlb(folio)));
+ __folio_mark_dirty(folio, mapping, !folio_test_fs_private(folio));
if (mapping->host) {
/* !PageAnon && !swapper_space */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index ac275eec086b9..29051c0f89881 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -955,8 +955,7 @@ static void folio_check_dirty_writeback(struct folio *folio,
*writeback = folio_test_writeback(folio);
/* Verify dirty/writeback state if the filesystem supports it */
- if (!(folio_test_private(folio) && !folio_test_swapcache(folio) &&
- !folio_test_hugetlb(folio)))
+ if (!folio_test_fs_private(folio))
return;
mapping = folio_mapping(folio);
--
2.53.0
^ permalink raw reply related [flat|nested] 14+ messages in thread* [PATCH v2 11/14] treewide: remove folio_set/clear_private()
2026-08-31 19:25 [PATCH v2 00/14] Remove PG_private by using page/folio->private checks instead Zi Yan
` (2 preceding siblings ...)
2026-08-31 19:25 ` [PATCH v2 10/14] mm/page-flags: introduce folio_test_fs_private() Zi Yan
@ 2026-08-31 19:25 ` Zi Yan
2026-08-31 19:25 ` [PATCH v2 14/14] mm/page-flags: remove PG_private Zi Yan
2026-09-03 16:10 ` [f2fs-dev] [PATCH v2 00/14] Remove PG_private by using page/folio->private checks instead patchwork-bot+f2fs
5 siblings, 0 replies; 14+ messages in thread
From: Zi Yan @ 2026-08-31 19:25 UTC (permalink / raw)
To: David Hildenbrand, Matthew Wilcox (Oracle), Andrew Morton,
Muchun Song, Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Baolin Wang,
Nico Pache, Ryan Roberts, Dev Jain, Barry Song, Lance Yang,
Usama Arif, Gregory Price, Ying Huang, Alistair Popple,
Johannes Weiner, Qi Zheng, Shakeel Butt, Kairui Song
Cc: linux-mm, linux-kernel, Zi Yan, Trond Myklebust, Anna Schumaker,
Jan Kara, Matthew Brost, Joshua Hahn, Rakie Kim, Byungchul Park,
linux-nfs, linux-fsdevel
They are no-ops now. Remove them.
Assisted-by: Claude:claude-opus-4-8
Assisted-by: Codex:gpt-5
Signed-off-by: Zi Yan <ziy@nvidia.com>
To: Trond Myklebust <trondmy@kernel.org>
To: Anna Schumaker <anna@kernel.org>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
To: Jan Kara <jack@suse.cz>
To: Andrew Morton <akpm@linux-foundation.org>
To: David Hildenbrand <david@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
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: linux-nfs@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-mm@kvack.org
---
fs/nfs/write.c | 2 --
include/linux/pagemap.h | 4 +---
mm/migrate.c | 1 -
3 files changed, 1 insertion(+), 6 deletions(-)
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 623e7ef1f73d5..b6967b5286691 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -717,7 +717,6 @@ static void nfs_inode_add_request(struct nfs_page *req)
nfs_lock_request(req);
spin_lock(&mapping->i_private_lock);
set_bit(PG_MAPPED, &req->wb_flags);
- folio_set_private(folio);
folio->private = req;
spin_unlock(&mapping->i_private_lock);
atomic_long_inc(&nfsi->nrequests);
@@ -745,7 +744,6 @@ static void nfs_inode_remove_request(struct nfs_page *req)
spin_lock(&mapping->i_private_lock);
folio->private = NULL;
- folio_clear_private(folio);
clear_bit(PG_MAPPED, &req->wb_head->wb_flags);
spin_unlock(&mapping->i_private_lock);
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 546e987d5cda7..88b4c92b43575 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -594,7 +594,6 @@ static inline void folio_attach_private(struct folio *folio, void *data)
{
folio_get(folio);
folio->private = data;
- folio_set_private(folio);
}
/**
@@ -629,9 +628,8 @@ static inline void *folio_detach_private(struct folio *folio)
{
void *data = folio_get_private(folio);
- if (!folio_test_private(folio))
+ if (!data)
return NULL;
- folio_clear_private(folio);
folio->private = NULL;
folio_put(folio);
diff --git a/mm/migrate.c b/mm/migrate.c
index 666a7365e16e8..5ca1548ca6d61 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -835,7 +835,6 @@ void folio_migrate_flags(struct folio *newfolio, struct folio *folio)
*/
if (folio_test_swapcache(folio))
folio_clear_swapcache(folio);
- folio_clear_private(folio);
/* page->private contains hugetlb specific flags */
if (!folio_test_hugetlb(folio))
--
2.53.0
^ permalink raw reply related [flat|nested] 14+ messages in thread* [PATCH v2 14/14] mm/page-flags: remove PG_private
2026-08-31 19:25 [PATCH v2 00/14] Remove PG_private by using page/folio->private checks instead Zi Yan
` (3 preceding siblings ...)
2026-08-31 19:25 ` [PATCH v2 11/14] treewide: remove folio_set/clear_private() Zi Yan
@ 2026-08-31 19:25 ` Zi Yan
2026-09-01 2:17 ` Zi Yan
` (2 more replies)
2026-09-03 16:10 ` [f2fs-dev] [PATCH v2 00/14] Remove PG_private by using page/folio->private checks instead patchwork-bot+f2fs
5 siblings, 3 replies; 14+ messages in thread
From: Zi Yan @ 2026-08-31 19:25 UTC (permalink / raw)
To: David Hildenbrand, Matthew Wilcox (Oracle), Andrew Morton,
Muchun Song, Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Baolin Wang,
Nico Pache, Ryan Roberts, Dev Jain, Barry Song, Lance Yang,
Usama Arif, Gregory Price, Ying Huang, Alistair Popple,
Johannes Weiner, Qi Zheng, Shakeel Butt, Kairui Song
Cc: linux-mm, linux-kernel, Zi Yan, Baoquan He, Pasha Tatashin,
Pratyush Yadav, Jonathan Corbet, Jan Kara, Steven Rostedt,
Masami Hiramatsu, Dave Young, Shuah Khan, Mathieu Desnoyers,
kexec, linux-doc, linux-fsdevel, linux-trace-kernel
folio->private != NULL indicates a folio carries private data, replacing
PG_private. All PG_private users are converted. Remove PG_private and
reserve the space as __PG_folio for future use.
Also update files in Documentation. hugetlbfs_reserv.rst is outdated and
left unchanged. It should be rewritten.
Assisted-by: Claude:claude-opus-4-8
Assisted-by: Codex:gpt-5
Signed-off-by: Zi Yan <ziy@nvidia.com>
To: Andrew Morton <akpm@linux-foundation.org>
To: Baoquan He <baoquan.he@linux.dev>
To: Mike Rapoport <rppt@kernel.org>
To: Pasha Tatashin <pasha.tatashin@soleen.com>
To: Pratyush Yadav <pratyush@kernel.org>
To: Jonathan Corbet <corbet@lwn.net>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
To: Jan Kara <jack@suse.cz>
To: David Hildenbrand <david@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Dave Young <ruirui.yang@linux.dev>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: "Liam R. Howlett" <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: kexec@lists.infradead.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-trace-kernel@vger.kernel.org
---
Documentation/admin-guide/kdump/vmcoreinfo.rst | 2 +-
Documentation/filesystems/vfs.rst | 6 +++---
include/linux/page-flags.h | 19 ++-----------------
include/trace/events/mmflags.h | 2 +-
kernel/vmcore_info.c | 1 -
5 files changed, 7 insertions(+), 23 deletions(-)
diff --git a/Documentation/admin-guide/kdump/vmcoreinfo.rst b/Documentation/admin-guide/kdump/vmcoreinfo.rst
index 7663c610fe901..5f1df6d080508 100644
--- a/Documentation/admin-guide/kdump/vmcoreinfo.rst
+++ b/Documentation/admin-guide/kdump/vmcoreinfo.rst
@@ -325,7 +325,7 @@ NR_FREE_PAGES
On linux-2.6.21 or later, the number of free pages is in
vm_stat[NR_FREE_PAGES]. Used to get the number of free pages.
-PG_lru|PG_private|PG_swapcache|PG_swapbacked|PG_hwpoison|PG_head_mask
+PG_lru|PG_swapcache|PG_swapbacked|PG_hwpoison|PG_head_mask
--------------------------------------------------------------------------
Page attributes. These flags are used to filter various unnecessary for
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index d3a93eec3945f..dec7816303c6a 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -649,8 +649,8 @@ Writeback.
The first can be used independently to the others. The VM can try to
release clean pages in order to reuse them. To do this it can call
-->release_folio on clean folios with the private
-flag set. Clean pages without PagePrivate and with no external references
+->release_folio on clean folios with folio->private set. Clean pages
+without folio->private set and with no external references
will be released without notice being given to the address_space.
To achieve this functionality, pages need to be placed on an LRU with
@@ -674,7 +674,7 @@ filemap_fdatawait_range, to wait for all writeback to complete.
An address_space handler may attach extra information to a page,
typically using the 'private' field in the 'struct page'. If such
-information is attached, the PG_Private flag should be set. This will
+information is attached, non-NULL 'private' field will
cause various VM routines to make extra calls into the address_space
handler to deal with that data.
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 9b585e68127a2..eb2961ed61018 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -44,10 +44,6 @@
* Consequently, PG_reserved for a page mapped into user space can indicate
* the zero page, the vDSO, MMIO pages or device memory.
*
- * The PG_private bitflag is set on pagecache pages if they contain filesystem
- * specific data (which is normally at page->private). It can be used by
- * private allocations for its own usage.
- *
* During initiation of disk I/O, PG_locked is set. This bit is set before I/O
* and cleared when writeback _starts_ or when read _completes_. PG_writeback
* is set before writeback starts and cleared when it finishes.
@@ -105,7 +101,7 @@ enum pageflags {
PG_owner_2, /* Owner use. If pagecache, fs may use */
PG_arch_1,
PG_reserved,
- PG_private, /* If pagecache, has fs-private data */
+ __PG_folio, /* Do not use: reserved for folio identification */
PG_private_2, /* If pagecache, has fs aux data */
PG_reclaim, /* To be reclaimed asap */
PG_swapbacked, /* Page is backed by RAM/swap */
@@ -576,7 +572,7 @@ 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
*/
static __always_inline bool folio_test_private(const struct folio *folio)
@@ -584,17 +580,6 @@ 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 */
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index 935893e5ea53b..caf090cd6f85e 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -144,7 +144,7 @@ TRACE_DEFINE_ENUM(___GFP_LAST_BIT);
DEF_PAGEFLAG_NAME(owner_2), \
DEF_PAGEFLAG_NAME(arch_1), \
DEF_PAGEFLAG_NAME(reserved), \
- DEF_PAGEFLAG_NAME(private), \
+ { 1UL << __PG_folio, "folio" }, \
DEF_PAGEFLAG_NAME(private_2), \
DEF_PAGEFLAG_NAME(writeback), \
DEF_PAGEFLAG_NAME(head), \
diff --git a/kernel/vmcore_info.c b/kernel/vmcore_info.c
index 8614430ca212a..5a417f8a922ab 100644
--- a/kernel/vmcore_info.c
+++ b/kernel/vmcore_info.c
@@ -216,7 +216,6 @@ static int __init crash_save_vmcoreinfo_init(void)
VMCOREINFO_LENGTH(free_area.free_list, MIGRATE_TYPES);
VMCOREINFO_NUMBER(NR_FREE_PAGES);
VMCOREINFO_NUMBER(PG_lru);
- VMCOREINFO_NUMBER(PG_private);
VMCOREINFO_NUMBER(PG_swapcache);
VMCOREINFO_NUMBER(PG_swapbacked);
#define PAGE_SLAB_MAPCOUNT_VALUE (PGTY_slab << 24)
--
2.53.0
^ permalink raw reply related [flat|nested] 14+ messages in thread* Re: [PATCH v2 14/14] mm/page-flags: remove PG_private
2026-08-31 19:25 ` [PATCH v2 14/14] mm/page-flags: remove PG_private Zi Yan
@ 2026-09-01 2:17 ` Zi Yan
2026-09-01 15:55 ` Steven Rostedt
2026-09-02 17:09 ` Usama Arif
2 siblings, 0 replies; 14+ messages in thread
From: Zi Yan @ 2026-09-01 2:17 UTC (permalink / raw)
To: David Hildenbrand, Matthew Wilcox (Oracle), Andrew Morton,
Muchun Song, Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Baolin Wang,
Nico Pache, Ryan Roberts, Dev Jain, Barry Song, Lance Yang,
Usama Arif, Gregory Price, Ying Huang, Alistair Popple,
Johannes Weiner, Qi Zheng, Shakeel Butt, Kairui Song
Cc: linux-mm, linux-kernel, Zi Yan, Baoquan He, Pasha Tatashin,
Pratyush Yadav, Jonathan Corbet, Jan Kara, Steven Rostedt,
Masami Hiramatsu, Dave Young, Shuah Khan, Mathieu Desnoyers,
kexec, linux-doc, linux-fsdevel, linux-trace-kernel
On Mon Aug 31, 2026 at 3:25 PM EDT, Zi Yan wrote:
> folio->private != NULL indicates a folio carries private data, replacing
> PG_private. All PG_private users are converted. Remove PG_private and
> reserve the space as __PG_folio for future use.
>
> Also update files in Documentation. hugetlbfs_reserv.rst is outdated and
> left unchanged. It should be rewritten.
>
<snip>
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 9b585e68127a2..eb2961ed61018 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -44,10 +44,6 @@
> * Consequently, PG_reserved for a page mapped into user space can indicate
> * the zero page, the vDSO, MMIO pages or device memory.
> *
> - * The PG_private bitflag is set on pagecache pages if they contain filesystem
> - * specific data (which is normally at page->private). It can be used by
> - * private allocations for its own usage.
> - *
> * During initiation of disk I/O, PG_locked is set. This bit is set before I/O
> * and cleared when writeback _starts_ or when read _completes_. PG_writeback
> * is set before writeback starts and cleared when it finishes.
> @@ -105,7 +101,7 @@ enum pageflags {
> PG_owner_2, /* Owner use. If pagecache, fs may use */
> PG_arch_1,
> PG_reserved,
> - PG_private, /* If pagecache, has fs-private data */
> + __PG_folio, /* Do not use: reserved for folio identification */
Sashiko asked how to detect leaked filesystem private data during page
free time after PG_private is removed.
Answer copied from RFC:
After the conversion, folio/page should have an elevated refcount whenever
->private is set. That would help detect leaked private data. I tried to
enforce ->private needs to be NULL at page free time[1], but that might
cause trouble for certain use cases.
[1] https://lore.kernel.org/all/20260223032641.1859381-1-ziy@nvidia.com/
--
Best Regards,
Yan, Zi
^ permalink raw reply [flat|nested] 14+ messages in thread* Re: [PATCH v2 14/14] mm/page-flags: remove PG_private
2026-08-31 19:25 ` [PATCH v2 14/14] mm/page-flags: remove PG_private Zi Yan
2026-09-01 2:17 ` Zi Yan
@ 2026-09-01 15:55 ` Steven Rostedt
2026-09-01 16:01 ` Zi Yan
2026-09-02 17:09 ` Usama Arif
2 siblings, 1 reply; 14+ messages in thread
From: Steven Rostedt @ 2026-09-01 15:55 UTC (permalink / raw)
To: Zi Yan
Cc: David Hildenbrand, Matthew Wilcox (Oracle), Andrew Morton,
Muchun Song, Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Baolin Wang,
Nico Pache, Ryan Roberts, Dev Jain, Barry Song, Lance Yang,
Usama Arif, Gregory Price, Ying Huang, Alistair Popple,
Johannes Weiner, Qi Zheng, Shakeel Butt, Kairui Song, linux-mm,
linux-kernel, Baoquan He, Pasha Tatashin, Pratyush Yadav,
Jonathan Corbet, Jan Kara, Masami Hiramatsu, Dave Young,
Shuah Khan, Mathieu Desnoyers, kexec, linux-doc, linux-fsdevel,
linux-trace-kernel
On Mon, 31 Aug 2026 15:25:37 -0400
Zi Yan <ziy@nvidia.com> wrote:
> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
> index 935893e5ea53b..caf090cd6f85e 100644
> --- a/include/trace/events/mmflags.h
> +++ b/include/trace/events/mmflags.h
> @@ -144,7 +144,7 @@ TRACE_DEFINE_ENUM(___GFP_LAST_BIT);
> DEF_PAGEFLAG_NAME(owner_2), \
> DEF_PAGEFLAG_NAME(arch_1), \
> DEF_PAGEFLAG_NAME(reserved), \
> - DEF_PAGEFLAG_NAME(private), \
> + { 1UL << __PG_folio, "folio" }, \
> DEF_PAGEFLAG_NAME(private_2), \
> DEF_PAGEFLAG_NAME(writeback), \
> DEF_PAGEFLAG_NAME(head), \
Hmm, just for consistency sake, can we create a:
#define __DEF_PAGEFLAG_NAME(_name) { 1UL << __PG_##_name, __stringify(_name) }
Which is similar to:
#define DEF_PAGEFLAG_NAME(_name) { 1UL << PG_##_name, __stringify(_name) }
But adds the "__" to the name. Then the above would look like:
DEF_PAGEFLAG_NAME(reserved), \
__DEF_PAGEFLAG_NAME(folio), \
DEF_PAGEFLAG_NAME(private_2), \
DEF_PAGEFLAG_NAME(writeback), \
Where the __DEF_PAGEFLAG_NAME() with the "__" still stands out, but the
code looks better than open coding it in the middle and making one wonder
why it was open coded. (It took me a bit to noticed the "__" difference.)
-- Steve
^ permalink raw reply [flat|nested] 14+ messages in thread* Re: [PATCH v2 14/14] mm/page-flags: remove PG_private
2026-09-01 15:55 ` Steven Rostedt
@ 2026-09-01 16:01 ` Zi Yan
2026-09-01 17:50 ` Steven Rostedt
0 siblings, 1 reply; 14+ messages in thread
From: Zi Yan @ 2026-09-01 16:01 UTC (permalink / raw)
To: Steven Rostedt
Cc: David Hildenbrand, Matthew Wilcox (Oracle), Andrew Morton,
Muchun Song, Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Baolin Wang,
Nico Pache, Ryan Roberts, Dev Jain, Barry Song, Lance Yang,
Usama Arif, Gregory Price, Ying Huang, Alistair Popple,
Johannes Weiner, Qi Zheng, Shakeel Butt, Kairui Song, linux-mm,
linux-kernel, Baoquan He, Pasha Tatashin, Pratyush Yadav,
Jonathan Corbet, Jan Kara, Masami Hiramatsu, Dave Young,
Shuah Khan, Mathieu Desnoyers, kexec, linux-doc, linux-fsdevel,
linux-trace-kernel
On 1 Sep 2026, at 11:55, Steven Rostedt wrote:
> On Mon, 31 Aug 2026 15:25:37 -0400
> Zi Yan <ziy@nvidia.com> wrote:
>
>> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
>> index 935893e5ea53b..caf090cd6f85e 100644
>> --- a/include/trace/events/mmflags.h
>> +++ b/include/trace/events/mmflags.h
>> @@ -144,7 +144,7 @@ TRACE_DEFINE_ENUM(___GFP_LAST_BIT);
>> DEF_PAGEFLAG_NAME(owner_2), \
>> DEF_PAGEFLAG_NAME(arch_1), \
>> DEF_PAGEFLAG_NAME(reserved), \
>> - DEF_PAGEFLAG_NAME(private), \
>> + { 1UL << __PG_folio, "folio" }, \
>> DEF_PAGEFLAG_NAME(private_2), \
>> DEF_PAGEFLAG_NAME(writeback), \
>> DEF_PAGEFLAG_NAME(head), \
>
> Hmm, just for consistency sake, can we create a:
>
> #define __DEF_PAGEFLAG_NAME(_name) { 1UL << __PG_##_name, __stringify(_name) }
>
> Which is similar to:
>
> #define DEF_PAGEFLAG_NAME(_name) { 1UL << PG_##_name, __stringify(_name) }
>
> But adds the "__" to the name. Then the above would look like:
>
> DEF_PAGEFLAG_NAME(reserved), \
> __DEF_PAGEFLAG_NAME(folio), \
> DEF_PAGEFLAG_NAME(private_2), \
> DEF_PAGEFLAG_NAME(writeback), \
>
> Where the __DEF_PAGEFLAG_NAME() with the "__" still stands out, but the
> code looks better than open coding it in the middle and making one wonder
> why it was open coded. (It took me a bit to noticed the "__" difference.)
>
No problem.
BTW, the plan is to add PG_folio after this series is picked up by Andrew/David.
So the new __DEF_PAGEFLAG_NAME() will have no user then and can be deleted.
It should be fine, right?
Best Regards,
Yan, Zi
^ permalink raw reply [flat|nested] 14+ messages in thread* Re: [PATCH v2 14/14] mm/page-flags: remove PG_private
2026-09-01 16:01 ` Zi Yan
@ 2026-09-01 17:50 ` Steven Rostedt
0 siblings, 0 replies; 14+ messages in thread
From: Steven Rostedt @ 2026-09-01 17:50 UTC (permalink / raw)
To: Zi Yan
Cc: David Hildenbrand, Matthew Wilcox (Oracle), Andrew Morton,
Muchun Song, Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Baolin Wang,
Nico Pache, Ryan Roberts, Dev Jain, Barry Song, Lance Yang,
Usama Arif, Gregory Price, Ying Huang, Alistair Popple,
Johannes Weiner, Qi Zheng, Shakeel Butt, Kairui Song, linux-mm,
linux-kernel, Baoquan He, Pasha Tatashin, Pratyush Yadav,
Jonathan Corbet, Jan Kara, Masami Hiramatsu, Dave Young,
Shuah Khan, Mathieu Desnoyers, kexec, linux-doc, linux-fsdevel,
linux-trace-kernel
On Tue, 01 Sep 2026 12:01:24 -0400
Zi Yan <ziy@nvidia.com> wrote:
> No problem.
>
> BTW, the plan is to add PG_folio after this series is picked up by Andrew/David.
> So the new __DEF_PAGEFLAG_NAME() will have no user then and can be deleted.
> It should be fine, right?
Yeah, then we just remove that macro and change the one user of
__DEF_PAGEFLAG_NAME() to DEF_PAGEFLAG_NAME().
It will make that patch even easier ;-)
-- Steve
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH v2 14/14] mm/page-flags: remove PG_private
2026-08-31 19:25 ` [PATCH v2 14/14] mm/page-flags: remove PG_private Zi Yan
2026-09-01 2:17 ` Zi Yan
2026-09-01 15:55 ` Steven Rostedt
@ 2026-09-02 17:09 ` Usama Arif
2026-09-02 17:57 ` Zi Yan
2 siblings, 1 reply; 14+ messages in thread
From: Usama Arif @ 2026-09-02 17:09 UTC (permalink / raw)
To: Zi Yan
Cc: Usama Arif, David Hildenbrand, Matthew Wilcox (Oracle),
Andrew Morton, Muchun Song, Lorenzo Stoakes, Liam R. Howlett,
Vlastimil Babka, Mike Rapoport, Suren Baghdasaryan, Michal Hocko,
Baolin Wang, Nico Pache, Ryan Roberts, Dev Jain, Barry Song,
Lance Yang, Gregory Price, Ying Huang, Alistair Popple,
Johannes Weiner, Qi Zheng, Shakeel Butt, Kairui Song, bhe, vgoyal,
dyoung, linux-mm, linux-kernel, Baoquan He, Pasha Tatashin,
Pratyush Yadav, Jonathan Corbet, Jan Kara, Steven Rostedt,
Masami Hiramatsu, Dave Young, Shuah Khan, Mathieu Desnoyers,
kexec, linux-doc, linux-fsdevel, linux-trace-kernel
On Mon, 31 Aug 2026 15:25:37 -0400 Zi Yan <ziy@nvidia.com> wrote:
> folio->private != NULL indicates a folio carries private data, replacing
> PG_private. All PG_private users are converted. Remove PG_private and
> reserve the space as __PG_folio for future use.
>
> Also update files in Documentation. hugetlbfs_reserv.rst is outdated and
> left unchanged. It should be rewritten.
>
> Assisted-by: Claude:claude-opus-4-8
> Assisted-by: Codex:gpt-5
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> To: Andrew Morton <akpm@linux-foundation.org>
> To: Baoquan He <baoquan.he@linux.dev>
> To: Mike Rapoport <rppt@kernel.org>
> To: Pasha Tatashin <pasha.tatashin@soleen.com>
> To: Pratyush Yadav <pratyush@kernel.org>
> To: Jonathan Corbet <corbet@lwn.net>
> To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> To: Jan Kara <jack@suse.cz>
> To: David Hildenbrand <david@kernel.org>
> To: Steven Rostedt <rostedt@goodmis.org>
> To: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Dave Young <ruirui.yang@linux.dev>
> Cc: Shuah Khan <skhan@linuxfoundation.org>
> Cc: Lorenzo Stoakes <ljs@kernel.org>
> Cc: "Liam R. Howlett" <liam@infradead.org>
> Cc: Vlastimil Babka <vbabka@kernel.org>
> Cc: Suren Baghdasaryan <surenb@google.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: kexec@lists.infradead.org
> Cc: linux-doc@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-fsdevel@vger.kernel.org
> Cc: linux-mm@kvack.org
> Cc: linux-trace-kernel@vger.kernel.org
> ---
> Documentation/admin-guide/kdump/vmcoreinfo.rst | 2 +-
> Documentation/filesystems/vfs.rst | 6 +++---
> include/linux/page-flags.h | 19 ++-----------------
> include/trace/events/mmflags.h | 2 +-
> kernel/vmcore_info.c | 1 -
> 5 files changed, 7 insertions(+), 23 deletions(-)
>
> diff --git a/Documentation/admin-guide/kdump/vmcoreinfo.rst b/Documentation/admin-guide/kdump/vmcoreinfo.rst
> index 7663c610fe901..5f1df6d080508 100644
> --- a/Documentation/admin-guide/kdump/vmcoreinfo.rst
> +++ b/Documentation/admin-guide/kdump/vmcoreinfo.rst
> @@ -325,7 +325,7 @@ NR_FREE_PAGES
> On linux-2.6.21 or later, the number of free pages is in
> vm_stat[NR_FREE_PAGES]. Used to get the number of free pages.
>
> -PG_lru|PG_private|PG_swapcache|PG_swapbacked|PG_hwpoison|PG_head_mask
> +PG_lru|PG_swapcache|PG_swapbacked|PG_hwpoison|PG_head_mask
> --------------------------------------------------------------------------
>
> Page attributes. These flags are used to filter various unnecessary for
> diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
> index d3a93eec3945f..dec7816303c6a 100644
> --- a/Documentation/filesystems/vfs.rst
> +++ b/Documentation/filesystems/vfs.rst
> @@ -649,8 +649,8 @@ Writeback.
>
> The first can be used independently to the others. The VM can try to
> release clean pages in order to reuse them. To do this it can call
> -->release_folio on clean folios with the private
> -flag set. Clean pages without PagePrivate and with no external references
> +->release_folio on clean folios with folio->private set. Clean pages
> +without folio->private set and with no external references
> will be released without notice being given to the address_space.
>
> To achieve this functionality, pages need to be placed on an LRU with
> @@ -674,7 +674,7 @@ filemap_fdatawait_range, to wait for all writeback to complete.
>
> An address_space handler may attach extra information to a page,
> typically using the 'private' field in the 'struct page'. If such
> -information is attached, the PG_Private flag should be set. This will
> +information is attached, non-NULL 'private' field will
> cause various VM routines to make extra calls into the address_space
> handler to deal with that data.
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 9b585e68127a2..eb2961ed61018 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -44,10 +44,6 @@
> * Consequently, PG_reserved for a page mapped into user space can indicate
> * the zero page, the vDSO, MMIO pages or device memory.
> *
> - * The PG_private bitflag is set on pagecache pages if they contain filesystem
> - * specific data (which is normally at page->private). It can be used by
> - * private allocations for its own usage.
> - *
> * During initiation of disk I/O, PG_locked is set. This bit is set before I/O
> * and cleared when writeback _starts_ or when read _completes_. PG_writeback
> * is set before writeback starts and cleared when it finishes.
> @@ -105,7 +101,7 @@ enum pageflags {
> PG_owner_2, /* Owner use. If pagecache, fs may use */
> PG_arch_1,
> PG_reserved,
> - PG_private, /* If pagecache, has fs-private data */
> + __PG_folio, /* Do not use: reserved for folio identification */
> PG_private_2, /* If pagecache, has fs aux data */
> PG_reclaim, /* To be reclaimed asap */
> PG_swapbacked, /* Page is backed by RAM/swap */
> @@ -576,7 +572,7 @@ 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
> */
>
> static __always_inline bool folio_test_private(const struct folio *folio)
> @@ -584,17 +580,6 @@ 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 */
> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
> index 935893e5ea53b..caf090cd6f85e 100644
> --- a/include/trace/events/mmflags.h
> +++ b/include/trace/events/mmflags.h
> @@ -144,7 +144,7 @@ TRACE_DEFINE_ENUM(___GFP_LAST_BIT);
> DEF_PAGEFLAG_NAME(owner_2), \
> DEF_PAGEFLAG_NAME(arch_1), \
> DEF_PAGEFLAG_NAME(reserved), \
> - DEF_PAGEFLAG_NAME(private), \
> + { 1UL << __PG_folio, "folio" }, \
> DEF_PAGEFLAG_NAME(private_2), \
> DEF_PAGEFLAG_NAME(writeback), \
> DEF_PAGEFLAG_NAME(head), \
> diff --git a/kernel/vmcore_info.c b/kernel/vmcore_info.c
> index 8614430ca212a..5a417f8a922ab 100644
> --- a/kernel/vmcore_info.c
> +++ b/kernel/vmcore_info.c
> @@ -216,7 +216,6 @@ static int __init crash_save_vmcoreinfo_init(void)
> VMCOREINFO_LENGTH(free_area.free_list, MIGRATE_TYPES);
> VMCOREINFO_NUMBER(NR_FREE_PAGES);
> VMCOREINFO_NUMBER(PG_lru);
> - VMCOREINFO_NUMBER(PG_private);
> VMCOREINFO_NUMBER(PG_swapcache);
> VMCOREINFO_NUMBER(PG_swapbacked);
> #define PAGE_SLAB_MAPCOUNT_VALUE (PGTY_slab << 24)
+ kdump maintainers and reviewers.
I believe makedumpfile reads VMCOREINFO. Removing it here, might cause issues
for older makedumpfile versions at crashdump?
Hopefully kdump folks will be able to comment better.
>
> --
> 2.53.0
>
>
^ permalink raw reply [flat|nested] 14+ messages in thread* Re: [PATCH v2 14/14] mm/page-flags: remove PG_private
2026-09-02 17:09 ` Usama Arif
@ 2026-09-02 17:57 ` Zi Yan
0 siblings, 0 replies; 14+ messages in thread
From: Zi Yan @ 2026-09-02 17:57 UTC (permalink / raw)
To: Usama Arif
Cc: David Hildenbrand, Matthew Wilcox (Oracle), Andrew Morton,
Muchun Song, Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Baolin Wang,
Nico Pache, Ryan Roberts, Dev Jain, Barry Song, Lance Yang,
Gregory Price, Ying Huang, Alistair Popple, Johannes Weiner,
Qi Zheng, Shakeel Butt, Kairui Song, bhe, vgoyal, dyoung,
linux-mm, linux-kernel, Baoquan He, Pasha Tatashin,
Pratyush Yadav, Jonathan Corbet, Jan Kara, Steven Rostedt,
Masami Hiramatsu, Dave Young, Shuah Khan, Mathieu Desnoyers,
kexec, linux-doc, linux-fsdevel, linux-trace-kernel
On 2 Sep 2026, at 13:09, Usama Arif wrote:
> On Mon, 31 Aug 2026 15:25:37 -0400 Zi Yan <ziy@nvidia.com> wrote:
>
>> folio->private != NULL indicates a folio carries private data, replacing
>> PG_private. All PG_private users are converted. Remove PG_private and
>> reserve the space as __PG_folio for future use.
>>
>> Also update files in Documentation. hugetlbfs_reserv.rst is outdated and
>> left unchanged. It should be rewritten.
>>
>> Assisted-by: Claude:claude-opus-4-8
>> Assisted-by: Codex:gpt-5
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>> To: Andrew Morton <akpm@linux-foundation.org>
>> To: Baoquan He <baoquan.he@linux.dev>
>> To: Mike Rapoport <rppt@kernel.org>
>> To: Pasha Tatashin <pasha.tatashin@soleen.com>
>> To: Pratyush Yadav <pratyush@kernel.org>
>> To: Jonathan Corbet <corbet@lwn.net>
>> To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
>> To: Jan Kara <jack@suse.cz>
>> To: David Hildenbrand <david@kernel.org>
>> To: Steven Rostedt <rostedt@goodmis.org>
>> To: Masami Hiramatsu <mhiramat@kernel.org>
>> Cc: Dave Young <ruirui.yang@linux.dev>
>> Cc: Shuah Khan <skhan@linuxfoundation.org>
>> Cc: Lorenzo Stoakes <ljs@kernel.org>
>> Cc: "Liam R. Howlett" <liam@infradead.org>
>> Cc: Vlastimil Babka <vbabka@kernel.org>
>> Cc: Suren Baghdasaryan <surenb@google.com>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
>> Cc: kexec@lists.infradead.org
>> Cc: linux-doc@vger.kernel.org
>> Cc: linux-kernel@vger.kernel.org
>> Cc: linux-fsdevel@vger.kernel.org
>> Cc: linux-mm@kvack.org
>> Cc: linux-trace-kernel@vger.kernel.org
>> ---
>> Documentation/admin-guide/kdump/vmcoreinfo.rst | 2 +-
>> Documentation/filesystems/vfs.rst | 6 +++---
>> include/linux/page-flags.h | 19 ++-----------------
>> include/trace/events/mmflags.h | 2 +-
>> kernel/vmcore_info.c | 1 -
>> 5 files changed, 7 insertions(+), 23 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kdump/vmcoreinfo.rst b/Documentation/admin-guide/kdump/vmcoreinfo.rst
>> index 7663c610fe901..5f1df6d080508 100644
>> --- a/Documentation/admin-guide/kdump/vmcoreinfo.rst
>> +++ b/Documentation/admin-guide/kdump/vmcoreinfo.rst
>> @@ -325,7 +325,7 @@ NR_FREE_PAGES
>> On linux-2.6.21 or later, the number of free pages is in
>> vm_stat[NR_FREE_PAGES]. Used to get the number of free pages.
>>
>> -PG_lru|PG_private|PG_swapcache|PG_swapbacked|PG_hwpoison|PG_head_mask
>> +PG_lru|PG_swapcache|PG_swapbacked|PG_hwpoison|PG_head_mask
>> --------------------------------------------------------------------------
>>
>> Page attributes. These flags are used to filter various unnecessary for
>> diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
>> index d3a93eec3945f..dec7816303c6a 100644
>> --- a/Documentation/filesystems/vfs.rst
>> +++ b/Documentation/filesystems/vfs.rst
>> @@ -649,8 +649,8 @@ Writeback.
>>
>> The first can be used independently to the others. The VM can try to
>> release clean pages in order to reuse them. To do this it can call
>> -->release_folio on clean folios with the private
>> -flag set. Clean pages without PagePrivate and with no external references
>> +->release_folio on clean folios with folio->private set. Clean pages
>> +without folio->private set and with no external references
>> will be released without notice being given to the address_space.
>>
>> To achieve this functionality, pages need to be placed on an LRU with
>> @@ -674,7 +674,7 @@ filemap_fdatawait_range, to wait for all writeback to complete.
>>
>> An address_space handler may attach extra information to a page,
>> typically using the 'private' field in the 'struct page'. If such
>> -information is attached, the PG_Private flag should be set. This will
>> +information is attached, non-NULL 'private' field will
>> cause various VM routines to make extra calls into the address_space
>> handler to deal with that data.
>>
>> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
>> index 9b585e68127a2..eb2961ed61018 100644
>> --- a/include/linux/page-flags.h
>> +++ b/include/linux/page-flags.h
>> @@ -44,10 +44,6 @@
>> * Consequently, PG_reserved for a page mapped into user space can indicate
>> * the zero page, the vDSO, MMIO pages or device memory.
>> *
>> - * The PG_private bitflag is set on pagecache pages if they contain filesystem
>> - * specific data (which is normally at page->private). It can be used by
>> - * private allocations for its own usage.
>> - *
>> * During initiation of disk I/O, PG_locked is set. This bit is set before I/O
>> * and cleared when writeback _starts_ or when read _completes_. PG_writeback
>> * is set before writeback starts and cleared when it finishes.
>> @@ -105,7 +101,7 @@ enum pageflags {
>> PG_owner_2, /* Owner use. If pagecache, fs may use */
>> PG_arch_1,
>> PG_reserved,
>> - PG_private, /* If pagecache, has fs-private data */
>> + __PG_folio, /* Do not use: reserved for folio identification */
>> PG_private_2, /* If pagecache, has fs aux data */
>> PG_reclaim, /* To be reclaimed asap */
>> PG_swapbacked, /* Page is backed by RAM/swap */
>> @@ -576,7 +572,7 @@ 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
>> */
>>
>> static __always_inline bool folio_test_private(const struct folio *folio)
>> @@ -584,17 +580,6 @@ 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 */
>> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
>> index 935893e5ea53b..caf090cd6f85e 100644
>> --- a/include/trace/events/mmflags.h
>> +++ b/include/trace/events/mmflags.h
>> @@ -144,7 +144,7 @@ TRACE_DEFINE_ENUM(___GFP_LAST_BIT);
>> DEF_PAGEFLAG_NAME(owner_2), \
>> DEF_PAGEFLAG_NAME(arch_1), \
>> DEF_PAGEFLAG_NAME(reserved), \
>> - DEF_PAGEFLAG_NAME(private), \
>> + { 1UL << __PG_folio, "folio" }, \
>> DEF_PAGEFLAG_NAME(private_2), \
>> DEF_PAGEFLAG_NAME(writeback), \
>> DEF_PAGEFLAG_NAME(head), \
>> diff --git a/kernel/vmcore_info.c b/kernel/vmcore_info.c
>> index 8614430ca212a..5a417f8a922ab 100644
>> --- a/kernel/vmcore_info.c
>> +++ b/kernel/vmcore_info.c
>> @@ -216,7 +216,6 @@ static int __init crash_save_vmcoreinfo_init(void)
>> VMCOREINFO_LENGTH(free_area.free_list, MIGRATE_TYPES);
>> VMCOREINFO_NUMBER(NR_FREE_PAGES);
>> VMCOREINFO_NUMBER(PG_lru);
>> - VMCOREINFO_NUMBER(PG_private);
>> VMCOREINFO_NUMBER(PG_swapcache);
>> VMCOREINFO_NUMBER(PG_swapbacked);
>> #define PAGE_SLAB_MAPCOUNT_VALUE (PGTY_slab << 24)
>
> + kdump maintainers and reviewers.
Thanks.
>
> I believe makedumpfile reads VMCOREINFO. Removing it here, might cause issues
> for older makedumpfile versions at crashdump?
The expectation is that kdump userspace tools will adapt to this change.
Later, PG_folio will be added to identify folios and has the same value
of PG_private, so preserving PG_private will not work then.
>
> Hopefully kdump folks will be able to comment better.
Best Regards,
Yan, Zi
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [f2fs-dev] [PATCH v2 00/14] Remove PG_private by using page/folio->private checks instead
2026-08-31 19:25 [PATCH v2 00/14] Remove PG_private by using page/folio->private checks instead Zi Yan
` (4 preceding siblings ...)
2026-08-31 19:25 ` [PATCH v2 14/14] mm/page-flags: remove PG_private Zi Yan
@ 2026-09-03 16:10 ` patchwork-bot+f2fs
5 siblings, 0 replies; 14+ messages in thread
From: patchwork-bot+f2fs @ 2026-09-03 16:10 UTC (permalink / raw)
To: Zi Yan
Cc: david, willy, akpm, muchun.song, ljs, liam, vbabka, rppt, surenb,
mhocko, baolin.wang, nico.pache, ryan.roberts, dev.jain, baohua,
lance.yang, usama.arif, gourry, ying.huang, apopple, hannes,
qi.zheng, shakeel.butt, kasong, mark.rutland, irogers, jack,
linux-doc, amarkuze, peterz, kexec, dave.hansen, ruirui.yang,
adrian.hunter, linux-mm, hongbohbli, hpa, guochunhai, skhan,
ceph-devel, baoquan.he, matthew.brost, anna, sstabellini,
zbestahu, rakie.kim, minchan, richard, x86, ebiggers,
alexander.shishkin, mingo, slava, weixugc, yukuai, xen-devel,
xiang, magiclinan, mhiramat, joshua.hahnjy, xiao, byungchul,
james.clark, acme, linux-raid, linux-fscrypt, bp, rostedt,
linux-mtd, axelrasmussen, jefflexu, namhyung, jaegeuk, yuanchu,
idryomov, osalvador, jgross, pratyush, linux-nfs, tytso,
oleksandr_tyshchenko, song, corbet, pasha.tatashin, linux-kernel,
linux-f2fs-devel, linux-perf-users, senozhatsky, tglx, jolsa,
linux-fsdevel, mathieu.desnoyers, linux-trace-kernel, linux-erofs,
trondmy
Hello:
This patch was applied to jaegeuk/f2fs.git (dev)
by Jaegeuk Kim <jaegeuk@kernel.org>:
On Mon, 31 Aug 2026 15:25:23 -0400 you wrote:
> Hi all,
>
> This patchset removes PG_private to make space for upcoming PG_folio
> (reserved as __PG_folio) for identifying pages from a folio (more details
> in Note below). Instead of checking PG_private, all code is changed to
> check page/folio->private != NULL instead.
>
> [...]
Here is the summary with links:
- [f2fs-dev,v2,06/14] f2fs: stop using PG_private
https://git.kernel.org/jaegeuk/f2fs/c/5ad9409a9533
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
^ permalink raw reply [flat|nested] 14+ messages in thread