mm/page-flags: check page/folio->private instead of PG_private

After the changes of the prior commits, page/folio->private != NULL is now
equivalent to checking PG_private.

Stop checking PG_private on pages and folios and use page/folio->private
instead, except swapcache and hugetlb folios, because the former uses a
field (swp_entry_t swap) overlapping with ->private and the latter sets
its flags in ->private.  Exclude swapcache and hugetlb when the code is
meant to check PG_private only.  PG_swapcache and folio->swap.val cannot
be set/clear as a whole, so excluding swapcache with
folio_test_swapcache() is not reliable.  Instead, use
folio_test_swapbacked(), since PG_swapbacked is stable when a folio is
added to/removed from swapcache.  Add a helper,
folio_has_attached_private(), for this check.

folio_test_private() and PagePrivate() now read folio/page->private
plainly instead of an atomic read of PG_private bit, so KCSAN complains
about possible data races.  Annotate them with data_race().

folio_expected_ref_count() can be called without the folio lock, so
annotate folio->mapping with data_race() while at it.

folio_set/clear_private() and Set/ClearPagePrivate() become no-ops.
PG_private is no longer checked at page free time. They will be removed in
an upcoming commit.

Remove KPF_PRIVATE since PG_private is no longer used.

Link: https://lore.kernel.org/20260920-remove-pg_private-v5-10-bb68b6a21869@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Assisted-by: LLM
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Liam R. Howlett" <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Nico Pache <nico.pache@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Qi Zheng <qi.zheng@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Kairui Song <kasong@tencent.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Wei Xu <weixugc@google.com>

1 files changed, 0 insertions, 1 deletions

diff --git a/include/linux/kernel-page-flags.h b/include/linux/kernel-page-flags.h
index 196778a087c4..fe5ab6e50bd7 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