Re: [PATCH] mm/migrate_device: Try to handle swapcache pages.

[Huang, Ying]

mpenttil@xxxxxxxxxx writes:

> From: Mika Penttilä <mpenttil@xxxxxxxxxx>
>
> 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.
>
> As a detail, do not mess with shmem pages, as they handle swap internally.
>
> Cc: Alistair Popple <apopple@xxxxxxxxxx>
> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
> Signed-off-by: Mika Penttilä <mpenttil@xxxxxxxxxx>
> ---
>  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 *src_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] &= ~MIGRATE_PFN_MIGRATE;
> -				continue;
> +				if (shmem_mapping(mapping) ||
> +				    !folio_free_swap(page_folio(page))) {

Should we filter out file pages firstly?

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

Best Regards,
Huang, Ying