Re: [PATCH 13/16] mm/migration: return errno when isolate_huge_page failed

[Miaohe Lin]

On 2022/3/9 9:00, Huang, Ying wrote:
> Miaohe Lin <linmiaohe@xxxxxxxxxx> writes:
> 
>> On 2022/3/7 13:07, Huang, Ying wrote:
>>> Miaohe Lin <linmiaohe@xxxxxxxxxx> 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@xxxxxxxxxx>
>>>> ---
>>>>  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?
> 
> I found the prototype of isolate_lru_page() is as follows,
> 
>   int isolate_lru_page(struct page *page)
> 
> And it will return errno directly.  I think we should follow same
> convention here?
> 

I see. Sounds reasonable to me. Will try to do it. Thanks.

> Best Regards,
> Huang, Ying
> .
>