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

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Message-ID: <D80D504B-20FC-4C2B-98EB-7694E9BAD64C@nvidia.com>
Date: Wed, 18 Jun 2025 14:04:18 -0400
From: Zi Yan <ziy@...dia.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
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Subject: Re: [PATCH RFC 04/29] mm/page_alloc: allow for making page types
 sticky until freed

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@...hat.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++;
> -- 
> 2.49.0

How does this preserve page type? Isn’t page->page_type = UINT_MAX clearing
page_type?

Best Regards,
Yan, Zi