linux-kernel - Re: [PATCH 3/4] mm/migration: return errno when isolate_huge

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Message-ID: <YlQ26kP8zpCLWqwW@infradead.org>
Date:   Mon, 11 Apr 2022 07:10:50 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, mike.kravetz@...cle.com,
        shy828301@...il.com, willy@...radead.org, ying.huang@...el.com,
        ziy@...dia.com, minchan@...nel.org, apopple@...dia.com,
        dave.hansen@...ux.intel.com, o451686892@...il.com,
        jhubbard@...dia.com, peterx@...hat.com, naoya.horiguchi@....com,
        mhocko@...e.com, riel@...hat.com, osalvador@...e.de,
        david@...hat.com, sfr@...b.auug.org.au, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] mm/migration: return errno when isolate_huge_page
 failed

On Sat, Apr 09, 2022 at 03:38:45PM +0800, Miaohe Lin wrote:
> We might fail to isolate huge page due to e.g. the page is under migration
> which cleared HPageMigratable. So we should return -EBUSY in this case
> rather than always return 1 which could confuse the user.
> 
> Fixes: e8db67eb0ded ("mm: migrate: move_pages() supports thp migration")
> Reviewed-by: Muchun Song <songmuchun@...edance.com>
> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/migrate.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 381963231a62..044656a14ae2 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1632,10 +1632,8 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
>  		goto out_putpage;
>  
>  	if (PageHuge(page)) {
> -		if (PageHead(page)) {
> -			isolate_huge_page(page, pagelist);
> -			err = 1;
> -		}
> +		if (PageHead(page))
> +			err = isolate_huge_page(page, pagelist) ? 1 : -EBUSY;

I think a:

			err = isolate_huge_page(page, pagelist);
			if (!err)
				err = 1;

would be a lot more readable here.