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

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Date:   Fri, 24 Jun 2022 17:45:50 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Huang Ying <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     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 6/24/2022 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;

Anyway this patch looks good to me.
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>

> 
> 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