linux-kernel - Re: [PATCH] mm: migrate: Do not retry 10 times for the subpages of fail-to-migrate THP

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Message-ID: <EC02F1E6-E201-4A8D-84B4-47758EA3F20A@nvidia.com>
Date:   Thu, 21 Jul 2022 11:48:09 -0400
From:   Zi Yan <ziy@...dia.com>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc:     akpm@...ux-foundation.org, ying.huang@...el.com,
        shy828301@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: migrate: Do not retry 10 times for the subpages of
 fail-to-migrate THP

On 21 Jul 2022, at 8:05, Baolin Wang wrote:

> If THP is failed to migrate due to -ENOSYS or -ENOMEM case, the THP will
> be split, and the subpages of fail-to-migrate THP will be tried to migrate
> again, so we should not account the retry counter in the second loop, since
> we already accounted 'nr_thp_failed' in the first loop.
>
> Moreover we also do not need retry 10 times for -EAGAIN case for the subpages
> of fail-to-migrate THP in the second loop, since we already regarded the
> THP as migration failure, and save some migration time (for the worst case,
> will try 512 * 10 times) according to previous discussion [1].
>
> [1] https://lore.kernel.org/linux-mm/87r13a7n04.fsf@yhuang6-desk2.ccr.corp.intel.com/
>
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
> Note, this patch is based on the patch set [1] from Huang Ying.
> [1] https://lore.kernel.org/linux-mm/20220711084948.274787-1-ying.huang@intel.com/
> ---
>  mm/migrate.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 8429206..e36a084 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1507,7 +1507,7 @@ 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++;
>  				nr_retry_pages += nr_subpages;
>  				break;
> @@ -1533,8 +1533,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>  			}
>  		}
>  	}
> -	if (!no_subpage_counting)
> -		nr_failed += retry;
> +	nr_failed += retry;
>  	nr_thp_failed += thp_retry;
>  	nr_failed_pages += nr_retry_pages;
>  	/*
> -- 
> 1.8.3.1

LGTM. Thanks. Reviewed-by: Zi Yan <ziy@...dia.com>

--
Best Regards,
Yan, Zi

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