mm/page-flags: remove PG_private

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.  Unused PG_private functions
are removed too.

Link: https://lore.kernel.org/20260920-remove-pg_private-v5-17-bb68b6a21869@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Assisted-by: LLM
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Pratyush Yadav <pratyush@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: 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>

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 */
@@ -588,18 +584,6 @@ static __always_inline bool folio_test_private(const struct folio *folio)
 	return data_race(folio->private);
 }
 
-static __always_inline int PagePrivate(const struct page *page)
-{
-	/* See folio_test_private() for data_race() use */
-	return !!data_race(page->private);
-}
-
-/* no-ops during transition */
-static __always_inline void folio_set_private(struct folio *folio) { }
-static __always_inline void folio_clear_private(struct folio *folio) { }
-static __always_inline void SetPagePrivate(struct page *page) { }
-static __always_inline void ClearPagePrivate(struct page *page) { }
-
 FOLIO_FLAG(private_2, FOLIO_HEAD_PAGE)
 
 /* owner_2 can be set on tail pages for anon memory */

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),					\
+	DEF_PAGEFLAG_NAME(folio),					\
 	DEF_PAGEFLAG_NAME(private_2),					\
 	DEF_PAGEFLAG_NAME(writeback),					\
 	DEF_PAGEFLAG_NAME(head),					\

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)