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

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Date:   Tue, 12 Apr 2022 11:13:16 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Christoph Hellwig <hch@...radead.org>
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 2022/4/11 22:10, Christoph Hellwig wrote:
> 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;

Many thanks for your comment. IIUC, isolate_huge_page does not return the wanted error code. So the
above code won't do the right thing.

Thanks.

> 
> would be a lot more readable here.
> 
> .
>