linux-kernel - Re: [PATCH v1 1/2] mm/migrate: remove MIGRATEPAGE

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Message-ID: <CABzRoyYU2yOuGQskCAG_gzKiQwR6uM9eAYqOOCoQj+Xv=r163A@mail.gmail.com>
Date: Wed, 13 Aug 2025 13:05:22 +0800
From: Lance Yang <lance.yang@...ux.dev>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	linuxppc-dev@...ts.ozlabs.org, virtualization@...ts.linux.dev, 
	linux-fsdevel@...r.kernel.org, linux-aio@...ck.org, 
	linux-btrfs@...r.kernel.org, jfs-discussion@...ts.sourceforge.net, 
	Andrew Morton <akpm@...ux-foundation.org>, Madhavan Srinivasan <maddy@...ux.ibm.com>, 
	Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, 
	Christophe Leroy <christophe.leroy@...roup.eu>, 
	Jerrin Shaji George <jerrin.shaji-george@...adcom.com>, Arnd Bergmann <arnd@...db.de>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Michael S. Tsirkin" <mst@...hat.com>, 
	Jason Wang <jasowang@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Eugenio Pérez <eperezma@...hat.com>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
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	David Sterba <dsterba@...e.com>, Muchun Song <muchun.song@...ux.dev>, 
	Oscar Salvador <osalvador@...e.de>, Dave Kleikamp <shaggy@...nel.org>, Zi Yan <ziy@...dia.com>, 
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	Rakie Kim <rakie.kim@...com>, Byungchul Park <byungchul@...com>, Gregory Price <gourry@...rry.net>, 
	Ying Huang <ying.huang@...ux.alibaba.com>, Alistair Popple <apopple@...dia.com>, 
	Minchan Kim <minchan@...nel.org>, Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH v1 1/2] mm/migrate: remove MIGRATEPAGE_UNMAP

On Mon, Aug 11, 2025 at 10:47 PM David Hildenbrand <david@...hat.com> wrote:
>
[...]
> +++ b/mm/migrate.c
> @@ -1176,16 +1176,6 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
>         bool locked = false;
>         bool dst_locked = false;
>
> -       if (folio_ref_count(src) == 1) {
> -               /* Folio was freed from under us. So we are done. */
> -               folio_clear_active(src);
> -               folio_clear_unevictable(src);
> -               /* free_pages_prepare() will clear PG_isolated. */
> -               list_del(&src->lru);
> -               migrate_folio_done(src, reason);
> -               return MIGRATEPAGE_SUCCESS;
> -       }
> -
>         dst = get_new_folio(src, private);
>         if (!dst)
>                 return -ENOMEM;
> @@ -1275,7 +1265,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
>
>         if (unlikely(page_has_movable_ops(&src->page))) {
>                 __migrate_folio_record(dst, old_page_state, anon_vma);
> -               return MIGRATEPAGE_UNMAP;
> +               return 0;
>         }
>
>         /*
> @@ -1305,7 +1295,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
>
>         if (!folio_mapped(src)) {
>                 __migrate_folio_record(dst, old_page_state, anon_vma);
> -               return MIGRATEPAGE_UNMAP;
> +               return 0;
>         }
>
>  out:
> @@ -1848,14 +1838,28 @@ static int migrate_pages_batch(struct list_head *from,
>                                 continue;
>                         }
>
> +                       /*
> +                        * If we are holding the last folio reference, the folio
> +                        * was freed from under us, so just drop our reference.
> +                        */
> +                       if (likely(!page_has_movable_ops(&folio->page)) &&
> +                           folio_ref_count(folio) == 1) {
> +                               folio_clear_active(folio);
> +                               folio_clear_unevictable(folio);
> +                               list_del(&folio->lru);
> +                               migrate_folio_done(folio, reason);
> +                               stats->nr_succeeded += nr_pages;
> +                               stats->nr_thp_succeeded += is_thp;
> +                               continue;
> +                       }
> +

It seems the reason parameter is no longer used within migrate_folio_unmap()
after this patch.

Perhaps it could be removed from the function's signature ;)

>                         rc = migrate_folio_unmap(get_new_folio, put_new_folio,
>                                         private, folio, &dst, mode, reason,
>                                         ret_folios);

Anyway, just a small thought. Feel free to add:
Reviewed-by: Lance Yang <lance.yang@...ux.dev>

Thanks,
Lance