linux-kernel - Re: [PATCH v2] mm/migrate_device: Try to handle swapcache pages

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Date:   Wed, 31 May 2023 15:24:32 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     mpenttil@...hat.com
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Alistair Popple <apopple@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>
Subject: Re: [PATCH v2] mm/migrate_device: Try to handle swapcache pages

mpenttil@...hat.com writes:

> From: Mika Penttilä <mpenttil@...hat.com>
>
> Migrating file pages and swapcache pages into device memory is not supported.
> The decision is done based on page_mapping(). For now, swapcache pages are not migrated.
>
> Things can however be improved, for swapcache pages. Try to get rid of the swap cache,
> and if successful, go ahead as with other anonymous pages.
>
> Cc: Alistair Popple <apopple@...dia.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> Cc: Ralph Campbell <rcampbell@...dia.com>
> Cc: Huang Ying <ying.huang@...el.com>
> Signed-off-by: Mika Penttilä <mpenttil@...hat.com>
> ---
>
> v2:
>   - use folio_test_anon() (Huang, Ying)
>
>  
>  mm/migrate_device.c | 24 ++++++++++++++++++------
>  1 file changed, 18 insertions(+), 6 deletions(-)
>
> diff --git a/mm/migrate_device.c b/mm/migrate_device.c
> index d30c9de60b0d..829bbc526758 100644
> --- a/mm/migrate_device.c
> +++ b/mm/migrate_device.c
> @@ -747,13 +747,25 @@ static void __migrate_device_pages(unsigned long *src_pfns,
>  
>  		if (is_device_private_page(newpage) ||
>  		    is_device_coherent_page(newpage)) {
> -			/*
> -			 * For now only support anonymous memory migrating to
> -			 * device private or coherent memory.
> -			 */
> +
>  			if (mapping) {
> -				src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
> -				continue;
> +				struct folio *folio;
> +
> +				folio = page_folio(page);
> +
> +				/*
> +				 * For now only support anonymous memory migrating to
> +				 * device private or coherent memory.
> +				 *
> +				 * Try to get rid of swap cache if possible.

I think we can delete the following 2 lines of comments.  They add
nothing except what code says already.

Otherwise looks good to me.

Reviewed-by: "Huang, Ying" <ying.huang@...el.com>

> +				 * page is here file or swapcache page, could be shmem also
> +				 * folio_test_anon() filters out file and shmem
> +				 *
> +				 */
> +				if (!folio_test_anon(folio) || !folio_free_swap(folio)) {
> +					src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
> +					continue;
> +				}
>  			}
>  		} else if (is_zone_device_page(newpage)) {
>  			/*