linux-kernel - Re: [PATCH 13/16] mm/migration: return errno when isolate_huge

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Date:   Mon, 7 Mar 2022 10:14:37 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     mike.kravetz@...cle.com, shy828301@...il.com, willy@...radead.org,
        ying.huang@...el.com, ziy@...dia.com, minchan@...nel.org,
        apopple@...dia.com, ave.hansen@...ux.intel.com,
        o451686892@...il.com, almasrymina@...gle.com, jhubbard@...dia.com,
        rcampbell@...dia.com, peterx@...hat.com, naoya.horiguchi@....com,
        mhocko@...e.com, riel@...hat.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/16] mm/migration: return errno when isolate_huge_page
 failed

Hi Miaohe,

On 3/4/2022 5:34 PM, Miaohe Lin wrote:
> We should return errno (-EBUSY here) when failed to isolate the huge page
> rather than always return 1 which could confuse the user.
> 
> 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 6c2dfed2ddb8..279940c0c064 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1618,10 +1618,8 @@ 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;

Could you elaborate on which case the huge page isolation can be failed 
in this case? Or you met a real problem? Cause now we've got this head 
huge page refcnt, I can not see why we'll fail to isolate this huge page.