Re: [PATCH 14/16] mm/huge_memory: fix comment of page_deferred_list

[Muchun Song]

On Thu, Jun 23, 2022 at 01:06:25AM +0800, Miaohe Lin wrote:
> The current comment is confusing because if global or memcg deferred list
> in the second tail page is occupied by compound_head, why we still use
> page[2].deferred_list here? I think it wants to say that Global or memcg
> deferred list in the first tail page is occupied by compound_mapcount and
> compound_pincount so we use the second tail page's deferred_list instead.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> ---
>  include/linux/huge_mm.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 12b297f9951d..2e8062b3417a 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -294,8 +294,8 @@ static inline bool thp_migration_supported(void)
>  static inline struct list_head *page_deferred_list(struct page *page)
>  {
>  	/*
> -	 * Global or memcg deferred list in the second tail pages is
> -	 * occupied by compound_head.
> +	 * Global or memcg deferred list in the first tail page is
> +	 * occupied by compound_mapcount and compound_pincount.
>  	 */

The structure of "struct page" seems to have told us the information that
we resue the 2nd tail page to be used as deferred_list. I am not sure the
value of those comments. Maybe better to remove them?

Thanks.

>  	return &page[2].deferred_list;
>  }
> -- 
> 2.23.0
> 
>