linux-kernel - Re: [PATCH] migrate_pages: modify max number of pages to migrate in batch

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Date: Tue, 25 Jun 2024 09:17:40 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Zhenneng Li <lizhenneng@...inos.cn>
Cc: Andrew Morton <akpm@...ux-foundation.org>,  linux-mm@...ck.org,
  linux-kernel@...r.kernel.org
Subject: Re: [PATCH] migrate_pages: modify max number of pages to migrate in
 batch

Hi, Zhenneng,

Zhenneng Li <lizhenneng@...inos.cn> writes:

> We restrict the number of pages to be migrated to no more than
> HPAGE_PMD_NR or NR_MAX_BATCHED_MIGRATION, but in fact, the
> number of pages to be migrated may reach 2*HPAGE_PMD_NR-1 or 2
> *NR_MAX_BATCHED_MIGRATION-1, it's not in inconsistent with the context.

Yes.  It's not HPAGE_PMD_NR exactly.

> Please refer to the patch: 42012e0436d4(migrate_pages: restrict number
> of pages to migrate in batch)
>
> Signed-off-by: Zhenneng Li <lizhenneng@...inos.cn>
> ---
>  mm/migrate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 781979567f64..7a4b37aac9e8 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1961,7 +1961,7 @@ int migrate_pages(struct list_head *from, new_folio_t get_new_folio,
>  			break;
>  	}
>  	if (nr_pages >= NR_MAX_BATCHED_MIGRATION)
> -		list_cut_before(&folios, from, &folio2->lru);
> +		list_cut_before(&folios, from, &folio->lru);

If the first entry of the list "from" is a THP with size HPAGE_PMD_NR,
"folio" will be the first entry of from, so that "folios" will be empty.
Right?

>  	else
>  		list_splice_init(from, &folios);
>  	if (mode == MIGRATE_ASYNC)

--
Best Regards,
Huang, Ying