Re: [PATCH v1 03/14] mm: add iomem vma selection for memory migration

Felix Kuehling
2021-08-25T14:24:31Z

Am 2021-08-24 um 11:48 p.m. schrieb Alex Sierra:
> In this case, this is used to migrate pages from device memory, back to
> system memory. This particular device memory type should be accessible
> by the CPU, through IOMEM access. Typically, zone device public type
> memory falls into this category.
>
> Signed-off-by: Alex Sierra <alex.sierra@amd.com>
> ---
> include/linux/migrate.h | 1 +
> mm/migrate.c | 3 ++-
> 2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 4bb4e519e3f5..6b16f417384f 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -156,6 +156,7 @@ static inline unsigned long migrate_pfn(unsigned long pfn)
> enum migrate_vma_direction {
> MIGRATE_VMA_SELECT_SYSTEM = 1 << 0,
> MIGRATE_VMA_SELECT_DEVICE_PRIVATE = 1 << 1,
> + MIGRATE_VMA_SELECT_IOMEM = 1 << 2,

How about calling this MIGRATE_VMA_SELECT_DEVICE_PUBLIC?

> };
>
> struct migrate_vma {
> diff --git a/mm/migrate.c b/mm/migrate.c
> index e3a10e2a1bb3..d4ae2da99607 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2406,7 +2406,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
> if (is_write_device_private_entry(entry))
> mpfn |= MIGRATE_PFN_WRITE;
> } else {
> - if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
> + if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM) &&
> + !(migrate->flags & MIGRATE_VMA_SELECT_IOMEM))
> goto next;

For MIGRATE_VMA_SELECT_IOMEM/DEVICE_PUBLIC, I think we should ensure the
pages are ZONE_DEVICE and we should also check the page owner for
symmetry with DEVICE_PRIVATE.

Regards,
Felix

> pfn = pte_pfn(pte);
> if (is_zero_pfn(pfn)) {