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From:   "Huang, Ying" <ying.huang@intel.com>
To:     mpenttil@redhat.com
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        apopple@nvidia.com, jhubbard@nvidia.com, rcampbell@nvidia.com
Subject: Re: [PATCH] mm/migrate_device: Try to handle swapcache pages.
References: <20230507061726.13422-1-mpenttil@redhat.com>
Date:   Mon, 08 May 2023 10:26:16 +0800
In-Reply-To: <20230507061726.13422-1-mpenttil@redhat.com>
        (mpenttil@redhat.com's message of "Sun, 7 May 2023 09:17:26 +0300")
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mpenttil@redhat.com writes:

> From: Mika Penttil=C3=A4 <mpenttil@redhat.com>
>
> Migrating file pages and swapcache pages into device memory is not suppor=
ted.
> The decision is done based on page_mapping(). For now, swapcache pages ar=
e not migrated.
>
> Things can however be improved, for swapcache pages. Try to get rid of th=
e swap cache,
> and if successful, go ahead as with other anonymous pages.
>
> As a detail, do not mess with shmem pages, as they handle swap internally.
>
> Cc: Alistair Popple <apopple@nvidia.com>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Ralph Campbell <rcampbell@nvidia.com>
> Signed-off-by: Mika Penttil=C3=A4 <mpenttil@redhat.com>
> ---
>  mm/migrate_device.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/mm/migrate_device.c b/mm/migrate_device.c
> index d30c9de60b0d..e8169c58c341 100644
> --- a/mm/migrate_device.c
> +++ b/mm/migrate_device.c
> @@ -12,6 +12,7 @@
>  #include <linux/mmu_notifier.h>
>  #include <linux/oom.h>
>  #include <linux/pagewalk.h>
> +#include <linux/shmem_fs.h>
>  #include <linux/rmap.h>
>  #include <linux/swapops.h>
>  #include <asm/tlbflush.h>
> @@ -750,10 +751,17 @@ static void __migrate_device_pages(unsigned long *s=
rc_pfns,
>  			/*
>  			 * For now only support anonymous memory migrating to
>  			 * device private or coherent memory.
> +			 *
> +			 * Try to get rid of swap cache if possible.
> +			 * Leave shmem pages alone, they handle swap internally
> +			 *
>  			 */
>  			if (mapping) {
> -				src_pfns[i] &=3D ~MIGRATE_PFN_MIGRATE;
> -				continue;
> +				if (shmem_mapping(mapping) ||
> +				    !folio_free_swap(page_folio(page))) {

Should we filter out file pages firstly?

> +					src_pfns[i] &=3D ~MIGRATE_PFN_MIGRATE;
> +					continue;
> +				}
>  			}
>  		} else if (is_zone_device_page(newpage)) {
>  			/*

Best Regards,
Huang, Ying