On 9/8/26 04:56, 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. 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.
>
> 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. Add data_race()
> annotation for other lockless callers 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 <[email protected]>
> To: Andrew Morton <[email protected]>
> To: David Hildenbrand <[email protected]>
> To: Steven Rostedt <[email protected]>
> To: Masami Hiramatsu <[email protected]>
> To: Lorenzo Stoakes <[email protected]>
> To: "Matthew Wilcox (Oracle)" <[email protected]>
> To: Jan Kara <[email protected]>
> To: Johannes Weiner <[email protected]>
> Cc: "Liam R. Howlett" <[email protected]>
> Cc: Vlastimil Babka <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Cc: Suren Baghdasaryan <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Mathieu Desnoyers <[email protected]>
> Cc: Zi Yan <[email protected]>
> Cc: Baolin Wang <[email protected]>
> Cc: Nico Pache <[email protected]>
> Cc: Ryan Roberts <[email protected]>
> Cc: Dev Jain <[email protected]>
> Cc: Barry Song <[email protected]>
> Cc: Lance Yang <[email protected]>
> Cc: Usama Arif <[email protected]>
> Cc: Matthew Brost <[email protected]>
> Cc: Joshua Hahn <[email protected]>
> Cc: Rakie Kim <[email protected]>
> Cc: Byungchul Park <[email protected]>
> Cc: Gregory Price <[email protected]>
> Cc: Ying Huang <[email protected]>
> Cc: Alistair Popple <[email protected]>
> Cc: Qi Zheng <[email protected]>
> Cc: Shakeel Butt <[email protected]>
> Cc: Kairui Song <[email protected]>
> Cc: Axel Rasmussen <[email protected]>
> Cc: Yuanchu Xie <[email protected]>
> Cc: Wei Xu <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> ---
[...]
> /* !PageAnon && !swapper_space */
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 40d3f1b48a74c..9348ebf9de882 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -978,7 +978,8 @@ 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_swapbacked(folio) &&
> + !folio_test_hugetlb(folio)))
Now that I read that check ... a fourth time? a fifth? I stopped counting :)
Should we have a (in light of folio_attach_private()):
static inline bool folio_has_attached_private(const struct folio *folio)
{
/* Careful, we might get called on unlocked folios. */
if (!data_race(folio->private))
return false;
/* On some folios ->private is used for different purposes. */
return !folio_test_swapbacked(folio) && !folio_test_hugetlb(folio);
}
Of course, adding some nice documentation what having attached private means?
--
Cheers,
David
