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

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Date:   Mon, 27 Jun 2022 09:46:31 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Baolin Wang <baolin.wang@...ux.alibaba.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

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.
TBH, I think that we should do that.  But because this has some behavior
change, it's better to be done in a separate patch?  Do you have
interest to do that on top of this patchset?

> 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