linux-kernel - Re: [PATCH] mm/mempolicy: clean up the code logic in queue_pages_pte

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Date:   Fri, 22 Apr 2022 13:48:00 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/mempolicy: clean up the code logic in
 queue_pages_pte_range

On Tue 19-04-22 20:22:34, Miaohe Lin wrote:
> Since commit e5947d23edd8 ("mm: mempolicy: don't have to split pmd for
> huge zero page"), THP is never splited in queue_pages_pmd. Thus 2 is
> never returned now. We can remove such unnecessary ret != 2 check and
> clean up the relevant comment. Minor improvements in readability.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>

Acked-by: Michal Hocko <mhocko@...e.com>
Thanks!

> ---
>  mm/mempolicy.c | 12 +++---------
>  1 file changed, 3 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 75a8b247f631..3934476fb708 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -441,12 +441,11 @@ static inline bool queue_pages_required(struct page *page,
>  }
>  
>  /*
> - * queue_pages_pmd() has four possible return values:
> + * queue_pages_pmd() has three possible return values:
>   * 0 - pages are placed on the right node or queued successfully, or
>   *     special page is met, i.e. huge zero page.
>   * 1 - there is unmovable page, and MPOL_MF_MOVE* & MPOL_MF_STRICT were
>   *     specified.
> - * 2 - THP was split.
>   * -EIO - is migration entry or only MPOL_MF_STRICT was specified and an
>   *        existing page was already on a node that does not follow the
>   *        policy.
> @@ -508,18 +507,13 @@ static int queue_pages_pte_range(pmd_t *pmd, unsigned long addr,
>  	struct page *page;
>  	struct queue_pages *qp = walk->private;
>  	unsigned long flags = qp->flags;
> -	int ret;
>  	bool has_unmovable = false;
>  	pte_t *pte, *mapped_pte;
>  	spinlock_t *ptl;
>  
>  	ptl = pmd_trans_huge_lock(pmd, vma);
> -	if (ptl) {
> -		ret = queue_pages_pmd(pmd, ptl, addr, end, walk);
> -		if (ret != 2)
> -			return ret;
> -	}
> -	/* THP was split, fall through to pte walk */
> +	if (ptl)
> +		return queue_pages_pmd(pmd, ptl, addr, end, walk);
>  
>  	if (pmd_trans_unstable(pmd))
>  		return 0;
> -- 
> 2.23.0

-- 
Michal Hocko
SUSE Labs