[PATCH v2 00/14] Remove PG_private by using page/folio->private checks instead

[PATCH v2 00/14] Remove PG_private by using page/folio->private checks instead

[Zi Yan]

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.

MM people are cc'd on all patches and subsystem people are cc'd on the
cover letter and corresponding patches.

Overview
===
Most code uses folio_attach/detach/change_private() functions, so folio
refcount is increased and decreased when folio->private is set and reset,
respectively. There is no need to change them.

Changes are needed for exceptional users:
1. zsmalloc uses PG_private to indicate first component zpdesc page and
   page->private is used to store zspage in zpdesc. To remove PG_private,
   is_first_zpdesc() is replaced by pointer comparison.

2. kernel/events/ring_buffer.c stores page order in page->private.
   Replacing PG_private with page->private != NULL works.

3. drivers/xen/grant-table.c stores xen_page_foreign in page->private,
   where on 32-bit, a pointer to xen_page_foreign is stored; on 64-bit,
   page->private is used as xen_page_foreign. PG_private check is replaced
   by page->private != NULL on 32-bit for xen_page_foreign deallocation.
   On 64-bit, page->private is cleared unconditionally since {domid=0,
   gref=0} (xen_page_foreign can be 0) is valid.

4. fs/crypto/crypto.c stores a folio pointer in page->private, PG_private
   checks are replaced by page->private != NULL.

5. fs/erofs has two different uses:

    5a. folio->private is used to form a reversed list of
    the outputs of readahead_folio(). readahead_folio_last() is added to
    output folios in reversed order, so that ->private is no longer needed.

    5b. folio->private is used as an in-flight I/O counter. Convert the
    code to use folio_attach/detach/get_private() and add bias==1 to the
    counter to avoid folio->private being zero.

6. fs/nfs/write.c: folio refcount maintenance is in a bigger scope than
   folio->private. So folio_attach/detach/get_private() is not used.
   Nothing to change.

7. fs/f2fs uses attach_page_private() to first reset folio->private then
   immediately sets PAGE_PRIVATE_NOT_POINTER bit on it. Change it to use
   attach_page_private() to set PAGE_PRIVATE_NOT_POINTER bit directly to
   avoid folio->private == NULL gap inside set_page_private_##name().

8. hugetlb uses folio_change_private(folio, NULL) without folio refcount
   maintenance. Change it to folio->private = NULL.

After the above changes, PG_private ops are converted to
page/folio->private ops.

folio_test_fs_private() is added to check filesystem-only private data by
excluding swapcache and hugetlb folios, because swapcache folios overlap
swp_entry_t swap with ->private and hugetlb sets its own flags in
->private.

Note
===
1. KPF_PRIVATE is removed after PG_private is removed.

2. Documentation/mm/hugetlbfs_reserv.rst is outdated, so I did not remove
   PG_private related text. It should be rewritten.

3. PG_folio is planned to be set on every page from a folio in
   page_rmappable_folio(), so folios with any order (currently
   PG_large_rmappable is used to identify >0 order folios) can be
   identified, vm_insert_*() can correctly reject all folios, and rmap code
   can accept only folios. Eventually, page_folio() will return NULL for
   non-folio pages by checking PG_folio, but before that all existing users
   that treat compound pages as folios will be converted. 

Tests
===
1. allmodconfig build passed.

2. zsmalloc is tested using ext4 on a 1GB lz4 zram:
    2a. zram load + zsmalloc compaction;
    2b. concurrent zspage migration via memory compaction;
    2c. confirmed that multi-page zspages actually formed.

    Details: https://github.com/x-y-z/linux-dev/blob/b4/remove-pg_private/test_zsmalloc.md

3. erofs is tested on images created with -C4096 and lz4hc, lzma,
   deflate, and zstd algorithms:
   3a. cold read of all files, verify checksums match source;
   3b. readahead + reclaim/migration race.

   Details: https://github.com/x-y-z/linux-dev/blob/b4/remove-pg_private/test_erofs.md

4. fscrypt is tested on software-encrypted ext4 with writes to exercise
   bounce pages.

   Details: https://github.com/x-y-z/linux-dev/blob/b4/remove-pg_private/test_fscrypt.md

5. f2fs is tested on an image with inline_data,compress_algorithm=lz4:
    5a. INLINE_INODE — lots of tiny files;
    5b. REF_RESOURCE + general writeback — buffered write churn with fsync;
    5c. ONGOING_MIGRATION — force GC / page migration;
    5d. ATOMIC_WRITE — atomic-write ioctl path.

    Details: https://github.com/x-y-z/linux-dev/blob/b4/remove-pg_private/test_f2fs.md
    (I did not run xfstests)

6. MM selftests passed.

LLM use
===
Claude was used to form a concrete plan on what code needs to be changed
and how to change them. The plan was reviewed by Codex until no issue was
spotted.

Plan is at: https://github.com/x-y-z/linux-dev/blob/b4/remove-pg_private/plan.md

I then followed the plan to make code changes. I did bounce ideas with
Claude how to change fs/erofs, since I did not like the original idea.
After each change, I asked Claude to review my code and git commit message.
I also asked Claude to give me test plans (see above).

At last, Codex was used to review all patches.

Comments and suggestions are welcome. Thanks.

Assisted-by: Claude:claude-opus-4-8
Assisted-by: Codex:gpt-5
Signed-off-by: Zi Yan <ziy@nvidia.com>
---
Changes in v2:
1. removed is_first_zpdesc() in patch 1 and open coded the checks.
2. fixed wording in patch 2's commit message and clarified page_private()
   also works when ring buffer's AUX page order is 0.
3. removed the empty loop in 64-bit gnttab_pages_set_private().
4. clarified folio->private will be reset to NULL by
   fscrypt_free_bounce_page() in the commit message.
5. clarified why hugetlb needs to restore hugetlb_vmemmap_optimized.
6. renamed readahead_folio_reverse() readahead_folio_last() and
   reimplemented readahead_folio_last() by adding a new readahead_control
   private member, _forward, and a new helper __readahead_advance().
7. added a bias, 1, to erofs I/O counter, so that folio->private stays non
   NULL between folio_attach_private() and folio_detach_private().
8. converted more call sites to use folio_test_fs_private().
- Link to v1: https://lore.kernel.org/r/20260731-remove-pg_private-v1-0-142c97ba3562@nvidia.com

---
Zi Yan (14):
      mm/zsmalloc: replace PG_private with pointer comparison
      perf/ring_buffer: stop using PG_private as AUX page high-order marker
      xen/grant-table: stop setting PG_private on pages for grant mapping
      fscrypt: stop setting PG_private on bounce page
      mm/hugetlb: use direct assignment instead of folio_change_private()
      f2fs: stop using PG_private
      erofs: mm/pagemap: add readahead_folio_last() to avoid folio->private
      erofs: use folio_attach/detach_private() instead of direct assignment
      mm/page-flags: check page/folio->private instead of PG_private
      mm/page-flags: introduce folio_test_fs_private()
      treewide: remove folio_set/clear_private()
      treewide: replace PagePrivate() with page_private()
      treewide: adjust comments on PagePrivate and PG_private
      mm/page-flags: remove PG_private

 Documentation/admin-guide/kdump/vmcoreinfo.rst |  2 +-
 Documentation/filesystems/vfs.rst              |  6 +--
 arch/x86/events/intel/bts.c                    |  3 --
 arch/x86/events/intel/pt.c                     |  6 +--
 drivers/md/md-bitmap.c                         |  6 +--
 drivers/xen/balloon.c                          |  5 +++
 drivers/xen/grant-table.c                      | 11 +++--
 fs/ceph/addr.c                                 |  8 ++--
 fs/crypto/crypto.c                             |  2 -
 fs/erofs/data.c                                | 16 ++++---
 fs/erofs/zdata.c                               | 13 ++----
 fs/f2fs/f2fs.h                                 |  8 ++--
 fs/nfs/file.c                                  |  4 +-
 fs/nfs/write.c                                 |  2 -
 fs/proc/page.c                                 |  1 -
 fs/ubifs/file.c                                |  8 ++--
 include/linux/buffer_head.h                    |  6 ---
 include/linux/kernel-page-flags.h              |  1 -
 include/linux/mm.h                             | 35 +++++++++------
 include/linux/mm_types.h                       |  4 +-
 include/linux/page-flags.h                     | 38 +++++++++++-----
 include/linux/pagemap.h                        | 60 +++++++++++++++++++++-----
 include/trace/events/mmflags.h                 |  2 +-
 include/trace/events/pagemap.h                 |  2 +-
 kernel/events/ring_buffer.c                    |  7 ++-
 kernel/vmcore_info.c                           |  1 -
 mm/huge_memory.c                               |  2 +-
 mm/hugetlb.c                                   |  6 +--
 mm/migrate.c                                   |  3 +-
 mm/page-writeback.c                            |  2 +-
 mm/vmscan.c                                    |  2 +-
 mm/zpdesc.h                                    |  2 +-
 mm/zsmalloc.c                                  | 24 +++--------
 tools/mm/page-types.c                          |  2 -
 34 files changed, 163 insertions(+), 137 deletions(-)
---
base-commit: 443451c85ca8d6389d34b1299decada62128f1fe
change-id: 20260728-remove-pg_private-cfe926c7f83c

Best regards,
--  
Yan, Zi

[PATCH v2 14/14] mm/page-flags: remove PG_private

[Zi Yan]

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

Re: [PATCH v2 14/14] mm/page-flags: remove PG_private

[Zi Yan]

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

Re: [PATCH v2 14/14] mm/page-flags: remove PG_private

[Steven Rostedt]

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

Re: [PATCH v2 14/14] mm/page-flags: remove PG_private

[Zi Yan]

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

Re: [PATCH v2 14/14] mm/page-flags: remove PG_private

[Steven Rostedt]

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

Re: [PATCH v2 14/14] mm/page-flags: remove PG_private

[Usama Arif]

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
> 
> 

Re: [PATCH v2 14/14] mm/page-flags: remove PG_private

[Zi Yan]

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