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

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Date:   Tue, 8 Mar 2022 20:12:28 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     "Huang, Ying" <ying.huang@...el.com>
CC:     <akpm@...ux-foundation.org>, <mike.kravetz@...cle.com>,
        <shy828301@...il.com>, <willy@...radead.org>, <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

On 2022/3/7 13:07, Huang, Ying wrote:
> Miaohe Lin <linmiaohe@...wei.com> writes:
> 
>> 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;
> 
> IMHO, it's better to determine the proper errno inside
> isolate_huge_page() instead of in the caller.  If you think it's
> necessary to get errno here.  How about change isolate_huge_page()
> instead?

IMO, -EBUSY should be enough for the user (as they could not do much) and this
errno keeps consistent with the non-hugetlb page case. What do you think?

Thanks.

> 
> Best Regards,
> Huang, Ying
> 
>>  	} else {
>>  		struct page *head;
> .
>