[PATCH RFC 04/29] mm/page_alloc: allow for making page types sticky until freed

[Zi Yan]

On 18 Jun 2025, at 13:39, David Hildenbrand wrote:

> Let's allow for not clearing a page type before freeing a page to the
> buddy.
>
> We'll focus on having a type set on the first page of a larger
> allocation only.
>
> With this change, we can reliably identify typed folios even though
> they might be in the process of getting freed, which will come in handy
> in migration code (at least in the transition phase).
>
> Signed-off-by: David Hildenbrand <david at redhat.com>
> ---
>  mm/page_alloc.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 858bc17653af9..44e56d31cfeb1 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1380,6 +1380,9 @@ __always_inline bool free_pages_prepare(struct page *page,
>  			mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);
>  		page->mapping = NULL;
>  	}
> +	if (unlikely(page_has_type(page)))
> +		page->page_type = UINT_MAX;
> +
>  	if (is_check_pages_enabled()) {
>  		if (free_page_is_bad(page))
>  			bad++;

Should we be pedantic to only do this for PageOffline and PageZsmalloc
and warn for the rest page types?

Something like:

if (unlikely(page_has_type(page))) {
	if (PageOffline(page) || PageZsmalloc(page))
		page->page_type = UINT_MAX;
	else
		VM_WARN_ONCE_PAGE(1, page);
}

Best Regards,
Yan, Zi