linux-kernel - Re: [PATCH v2] mm/nommu: convert kobjsize() to folios

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Message-ID: <a12fc401-59bd-4005-b1f9-fcaa1f68f68b@suse.cz>
Date: Mon, 4 Aug 2025 17:33:33 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Sidhartha Kumar <sidhartha.kumar@...cle.com>, linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org, willy@...radead.org,
 jannh@...gle.com, pfalcato@...e.de, lorenzo.stoakes@...cle.com,
 Liam.Howlett@...cle.com, SeongJae Park <sj@...nel.org>
Subject: Re: [PATCH v2] mm/nommu: convert kobjsize() to folios

On 8/4/25 16:51, Sidhartha Kumar wrote:
> Simple folio conversion to remove a user of PageSlab() and
> PageCompound().
> 
> Reviewed-by: SeongJae Park <sj@...nel.org>
> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>

Ok a stupid question maybe... why does this code exists at all? AFAICS only
that fs/proc/task_nommu.c can report how much bytes the kernel objects take
for a task? That code seems to be from pre-git era. Does anyone care today?

> ---
> v1 -> v2:
> 	change "compound folio" to "large folio" in comment per SJ
> 
>  mm/nommu.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 07504d666d6a..75548fae28f7 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -64,7 +64,7 @@ const struct vm_operations_struct generic_file_vm_ops = {
>   */
>  unsigned int kobjsize(const void *objp)
>  {
> -	struct page *page;
> +	struct folio *folio;
>  
>  	/*
>  	 * If the object we have should not have ksize performed on it,
> @@ -73,22 +73,22 @@ unsigned int kobjsize(const void *objp)
>  	if (!objp || !virt_addr_valid(objp))
>  		return 0;
>  
> -	page = virt_to_head_page(objp);
> +	folio = virt_to_folio(objp);
>  
>  	/*
>  	 * If the allocator sets PageSlab, we know the pointer came from
>  	 * kmalloc().
>  	 */
> -	if (PageSlab(page))
> +	if (folio_test_slab(folio))
>  		return ksize(objp);
>  
>  	/*
> -	 * If it's not a compound page, see if we have a matching VMA
> +	 * If it's not a large folio, see if we have a matching VMA
>  	 * region. This test is intentionally done in reverse order,
>  	 * so if there's no VMA, we still fall through and hand back
> -	 * PAGE_SIZE for 0-order pages.
> +	 * PAGE_SIZE for 0-order folios.
>  	 */
> -	if (!PageCompound(page)) {
> +	if (!folio_test_large(folio)) {
>  		struct vm_area_struct *vma;
>  
>  		vma = find_vma(current->mm, (unsigned long)objp);
> @@ -100,7 +100,7 @@ unsigned int kobjsize(const void *objp)
>  	 * The ksize() function is only guaranteed to work for pointers
>  	 * returned by kmalloc(). So handle arbitrary pointers here.
>  	 */
> -	return page_size(page);
> +	return folio_size(folio);
>  }
>  
>  void vfree(const void *addr)