Re: [PATCH v4 15/16] kasan: Remove references to folio in __kasan_mempool_poison_object()

[Harry Yoo <harry.yoo@oracle.com>]

On Thu, Nov 13, 2025 at 12:09:29AM +0000, Matthew Wilcox (Oracle) wrote:
> In preparation for splitting struct slab from struct page and struct
> folio, remove mentions of struct folio from this function.  There is a
> mild improvement for large kmalloc objects as we will avoid calling
> compound_head() for them.  We can discard the comment as using
> PageLargeKmalloc() rather than !folio_test_slab() makes it obvious.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Acked-by: David Hildenbrand <david@redhat.com>
> Cc: Alexander Potapenko <glider@google.com>
> Cc: Andrey Konovalov <andreyknvl@gmail.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
> Cc: kasan-dev <kasan-dev@googlegroups.com>
> ---

Acked-by: Harry Yoo <harry.yoo@oracle.com>

>  mm/kasan/common.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 22e5d67ff064..1d27f1bd260b 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -517,24 +517,20 @@ void __kasan_mempool_unpoison_pages(struct page *page, unsigned int order,
>  
>  bool __kasan_mempool_poison_object(void *ptr, unsigned long ip)
>  {
> -	struct folio *folio = virt_to_folio(ptr);
> +	struct page *page = virt_to_page(ptr);
>  	struct slab *slab;
>  
> -	/*
> -	 * This function can be called for large kmalloc allocation that get
> -	 * their memory from page_alloc. Thus, the folio might not be a slab.
> -	 */
> -	if (unlikely(!folio_test_slab(folio))) {
> +	if (unlikely(PageLargeKmalloc(page))) {

nit: no strong opinion from me, but maybe KASAN folks still want to catch
!PageLargeKmalloc() && !slab case gracefully, as they care more about
detecting invalid frees than performance.


>  		if (check_page_allocation(ptr, ip))
>  			return false;
> -		kasan_poison(ptr, folio_size(folio), KASAN_PAGE_FREE, false);
> +		kasan_poison(ptr, page_size(page), KASAN_PAGE_FREE, false);
>  		return true;
>  	}
>  
>  	if (is_kfence_address(ptr))
>  		return true;
>  
> -	slab = folio_slab(folio);
> +	slab = page_slab(page);
>  
>  	if (check_slab_allocation(slab->slab_cache, ptr, ip))
>  		return false;
> -- 
> 2.47.2

-- 
Cheers,
Harry / Hyeonggon