On Fri Jul 31, 2026 at 10:13 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 hugetlbfs_reserv.rst is outdated and 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. > > Assisted-by: Claude:claude-opus-4-8 > Assisted-by: Codex:gpt-5 > Signed-off-by: Zi Yan <[email protected]> > To: Andrew Morton <[email protected]> > To: Baoquan He <[email protected]> > To: Mike Rapoport <[email protected]> > To: Pasha Tatashin <[email protected]> > To: Pratyush Yadav <[email protected]> > To: Jonathan Corbet <[email protected]> > To: "Matthew Wilcox (Oracle)" <[email protected]> > To: Jan Kara <[email protected]> > To: David Hildenbrand <[email protected]> > To: Steven Rostedt <[email protected]> > To: Masami Hiramatsu <[email protected]> > Cc: Dave Young <[email protected]> > Cc: Shuah Khan <[email protected]> > Cc: Lorenzo Stoakes <[email protected]> > Cc: "Liam R. Howlett" <[email protected]> > Cc: Vlastimil Babka <[email protected]> > Cc: Suren Baghdasaryan <[email protected]> > Cc: Michal Hocko <[email protected]> > Cc: Mathieu Desnoyers <[email protected]> > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > --- > 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 e7677423a20f7..5cc07f82fe371 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 0e3628ea080c4..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: 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/[email protected]/ <snip> > 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) Sashiko asked if removing PG_private from vmcoreinfo breaks back compatiblity for related userspace tools. Answer: Userspace tools will adapt to the changes. -- Best Regards, Yan, Zi
