Re: [PATCH v3 05/14] mm/hugetlb: use direct assignment instead of folio_change_private()

[David Hildenbrand (Arm)]

On 9/8/26 04:56, Zi Yan wrote:
> folio_change_private() should be used along with folio_attach_private() and
> folio_detach_private(), where adding and remove ->private content requires
> folio refcount change. add_hugetlb_folio() simply sets folio->private to
> NULL without refcount manipulation. Change it to direct assignment to avoid
> semantic confusion.
> 
> It prepares for a future commit that remove PG_private.
> 
> No functional change intended.
> 
> Assisted-by: Claude:claude-opus-4-8
> Assisted-by: Codex:gpt-5
> To: Muchun Song <muchun.song@xxxxxxxxx>
> To: Oscar Salvador <osalvador@xxxxxxx>
> To: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Acked-by: Usama Arif <usama.arif@xxxxxxxxx>
> Reviewed-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---
>  mm/hugetlb.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index a69bd463b1aef..08a538739d785 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1445,10 +1445,10 @@ void add_hugetlb_folio(struct hstate *h, struct folio *folio,
>  	}
>  
>  	__folio_set_hugetlb(folio);
> -	folio_change_private(folio, NULL);
> +	folio->private = NULL;
>  	/*
> -	 * We have to set hugetlb_vmemmap_optimized again as above
> -	 * folio_change_private(folio, NULL) cleared it.
> +	 * The hugetlb flags live in folio->private and are cleared by the above
> +	 * assignment. Restore the hugetlb_vmemmap_optimized flag.

"are cleared by the above assignment" ... isn't "folio->private = NULL;" as
self-documenting as it gets? :)

	"Clear all folio->private flags except hugetlb_vmemmap_optimized."
	folio->private = NULL;
	folio_set_hugetlb_vmemmap_optimized(folio);

Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

It's also pretty odd that we use an atomic here, when just erasing all flags ...
but that's something for another day.
-- 
Cheers,

David