linux-kernel - Re: [PATCH 4/7] migrate_pages(): fix failure counting for THP subpages retrying

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Date:   Mon, 27 Jun 2022 11:59:50 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Zi Yan <ziy@...dia.com>,
        Yang Shi <shy828301@...il.com>
Subject: Re: [PATCH 4/7] migrate_pages(): fix failure counting for THP
 subpages retrying



On 6/27/2022 9:46 AM, Huang, Ying wrote:
> Baolin Wang <baolin.wang@...ux.alibaba.com> writes:
> 
>> On 6/24/2022 10:53 AM, Huang Ying wrote:
>>> If THP is failed to be migrated for -ENOSYS and -ENOMEM, the THP will
>>> be split into thp_split_pages, and after other pages are migrated,
>>> pages in thp_split_pages will be migrated with no_subpage_counting ==
>>> true, because its failure have been counted already.  If some pages in
>>> thp_split_pages are retried during migration, we should not count
>>> their failure if no_subpage_counting == true too.  This is done this
>>> patch to fix the failure counting for THP subpages retrying.
>>
>> Good catch. Totally agree with you. It seems we can move the condition
>> into -EAGAIN case like other cases did?
>>
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 1ece23d80bc4..491c2d07402b 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -1463,7 +1463,7 @@ int migrate_pages(struct list_head *from,
>> new_page_t get_new_page,
>>                          case -EAGAIN:
>>                                  if (is_thp)
>>                                          thp_retry++;
>> -                               else
>> +                               else if (!no_subpage_counting)
>>                                          retry++;
>>                                  break;
> 
> This has another effect except fixing the failure counting.  That is,
> the split subpages of THP will not be retried for 10 times for -EAGAIN.

Ah, yes.

> TBH, I think that we should do that.  But because this has some behavior

OK. So you afraid that 10 times retry for each subpage of THP will waste 
lots of time?

> change, it's better to be done in a separate patch?  Do you have
> interest to do that on top of this patchset?

Sure. I can send a patch which can be folded into your series. Is this 
OK for you?

By the way, if I do like I said, the patch 4 can be avoided.

> 
>> Anyway this patch looks good to me.
>> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> 
> Thanks!
> 
> Best Regards,
> Huang, Ying
> 
>>> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
>>> Fixes: 5984fabb6e82 ("mm: move_pages: report the number of non-attempted pages")
>>> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
>>> Cc: Zi Yan <ziy@...dia.com>
>>> Cc: Yang Shi <shy828301@...il.com>
>>> --- >   mm/migrate.c | 3 ++-
>>>    1 file changed, 2 insertions(+), 1 deletion(-)
>>> diff --git a/mm/migrate.c b/mm/migrate.c
>>> index 542533e4e3cf..61dab3025a1d 100644
>>> --- a/mm/migrate.c
>>> +++ b/mm/migrate.c
>>> @@ -1477,7 +1477,8 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>>    			}
>>>    		}
>>>    	}
>>> -	nr_failed += retry;
>>> +	if (!no_subpage_counting)
>>> +		nr_failed += retry;
>>>    	nr_thp_failed += thp_retry;
>>>    	/*
>>>    	 * Try to migrate subpages of fail-to-migrate THPs, no nr_failed