linux-kernel - Re: [PATCH v2 2/9] mm/vmscan: remove unneeded can_split_huge

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Message-ID: <YlQ4w907eRUrBabJ@infradead.org>
Date:   Mon, 11 Apr 2022 07:18:43 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, ying.huang@...el.com,
        songmuchun@...edance.com, hch@...radead.org, willy@...radead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/9] mm/vmscan: remove unneeded can_split_huge_page
 check

On Sat, Apr 09, 2022 at 05:34:53PM +0800, Miaohe Lin wrote:
> We don't need to check can_split_folio() because folio_maybe_dma_pinned()
> is checked before. It will avoid the long term pinned pages to be swapped
> out. And we can live with short term pinned pages. Without can_split_folio
> checking we can simplify the code. Also activate_locked can be changed to
> keep_locked as it's just short term pinning.
> 
> Suggested-by: Huang, Ying <ying.huang@...el.com>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/vmscan.c | 22 ++++++++--------------
>  1 file changed, 8 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 4a76be47bed1..01f5db75a507 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1711,20 +1711,14 @@ static unsigned int shrink_page_list(struct list_head *page_list,
>  					goto keep_locked;
>  				if (folio_maybe_dma_pinned(folio))
>  					goto keep_locked;
> -				if (PageTransHuge(page)) {
> -					/* cannot split THP, skip it */
> -					if (!can_split_folio(folio, NULL))
> -						goto activate_locked;
> -					/*
> -					 * Split pages without a PMD map right
> -					 * away. Chances are some or all of the
> -					 * tail pages can be freed without IO.
> -					 */
> -					if (!folio_entire_mapcount(folio) &&
> -					    split_folio_to_list(folio,
> -								page_list))
> -						goto activate_locked;
> -				}
> +				/*
> +				 * Split pages without a PMD map right
> +				 * away. Chances are some or all of the
> +				 * tail pages can be freed without IO.
> +				 */

This could use more of the line length and be more readable:

				/*
				 * Split pages without a PMD map right away.
				 * Chances are some or all of the tail pages
				 * can be freed without IO.
				 */

> +				if (PageTransHuge(page) && !folio_entire_mapcount(folio) &&

Please put the folio_entire_mapcoun ont a separate line to make this a
bit more redable.