Re: [PATCH v3 08/16] mm/rmap: drop "compound" parameter from page_add_new_anon_rmap()

[Vlastimil Babka]

On 3/29/22 18:04, David Hildenbrand wrote:
> New anonymous pages are always mapped natively: only THP/khugepagd code

						khugepaged ^

> maps a new compound anonymous page and passes "true". Otherwise, we're
> just dealing with simple, non-compound pages.
> 
> Let's give the interface clearer semantics and document these.
> 
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

Nit:

> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1182,19 +1182,22 @@ void page_add_anon_rmap(struct page *page,
>  }
>  
>  /**
> - * page_add_new_anon_rmap - add pte mapping to a new anonymous page
> + * page_add_new_anon_rmap - add mapping to a new anonymous page
>   * @page:	the page to add the mapping to
>   * @vma:	the vm area in which the mapping is added
>   * @address:	the user virtual address mapped
> - * @compound:	charge the page as compound or small page
> + *
> + * If it's a compound page, it is accounted as a compound page. As the page
> + * is new, it's assume to get mapped exclusively by a single process.
>   *
>   * Same as page_add_anon_rmap but must only be called on *new* pages.
>   * This means the inc-and-test can be bypassed.
>   * Page does not have to be locked.
>   */
>  void page_add_new_anon_rmap(struct page *page,
> -	struct vm_area_struct *vma, unsigned long address, bool compound)
> +	struct vm_area_struct *vma, unsigned long address)
>  {
> +	const bool compound = PageCompound(page);
>  	int nr = compound ? thp_nr_pages(page) : 1;
>  
>  	VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);

There's a VM_BUG_ON_PAGE(PageTransCompound(page), page); later in a
!compound branch. Since compound is now determined by the same check, could
be deleted.