[v5,02/10] mm: add device coherent vma selection for memory migration

Commit Message

Sierra Guiza, Alejandro (Alex) Jan. 28, 2022, 8:08 p.m. UTC

This case is used to migrate pages from device memory, back to system
memory. Device coherent type memory is cache coherent from device and CPU
point of view.

Signed-off-by: Alex Sierra <[e-mail]>
Acked-by: Felix Kuehling <[e-mail]>
---
v2:
condition added when migrations from device coherent pages.
---
 include/linux/migrate.h |  1 +
 mm/migrate.c            | 10 +++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

Comments

Alistair Popple Jan. 31, 2022, 6:32 a.m. UTC | #1

On Saturday, 29 January 2022 7:08:17 AM AEDT Alex Sierra wrote:

[...]

>  struct migrate_vma {
> diff --git a/mm/migrate.c b/mm/migrate.c
> index cd137aedcfe5..d3cc3589e1e8 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2264,7 +2264,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
>  			if (is_writable_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_DEVICE_COHERENT))
>  				goto next;
>  			pfn = pte_pfn(pte);
>  			if (is_zero_pfn(pfn)) {

Sorry, but I still don't think this is quite right.

When specifying MIGRATE_VMA_SELECT_DEVICE_COHERENT we are looking for pages to
migrate from the device back to system memory. But as currently written I think
this can also select the zero pfn when MIGRATE_VMA_SELECT_DEVICE_COHERENT is
specified. As far as I know that can never point to device memory so migration
of a zero pfn should be also be skipped in that case.

We should only migrate the zero pfn if MIGRATE_VMA_SELECT_SYSTEM is specified.

> @@ -2273,6 +2274,13 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
>  				goto next;
>  			}
>  			page = vm_normal_page(migrate->vma, addr, pte);
> +			if (page && !is_zone_device_page(page) &&
> +			    !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
> +				goto next;
> +			if (page && is_device_coherent_page(page) &&
> +			    (!(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_COHERENT) ||
> +			     page->pgmap->owner != migrate->pgmap_owner))
> +				goto next;
>  			mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
>  			mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
>  		}
>

Patch

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index db96e10eb8da..66a34eae8cb6 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -130,6 +130,7 @@  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_DEVICE_COHERENT = 1 << 2,
 };
 
 struct migrate_vma {
diff --git a/mm/migrate.c b/mm/migrate.c
index cd137aedcfe5..d3cc3589e1e8 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2264,7 +2264,8 @@  static int migrate_vma_collect_pmd(pmd_t *pmdp,
 			if (is_writable_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_DEVICE_COHERENT))
 				goto next;
 			pfn = pte_pfn(pte);
 			if (is_zero_pfn(pfn)) {
@@ -2273,6 +2274,13 @@  static int migrate_vma_collect_pmd(pmd_t *pmdp,
 				goto next;
 			}
 			page = vm_normal_page(migrate->vma, addr, pte);
+			if (page && !is_zone_device_page(page) &&
+			    !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
+				goto next;
+			if (page && is_device_coherent_page(page) &&
+			    (!(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_COHERENT) ||
+			     page->pgmap->owner != migrate->pgmap_owner))
+				goto next;
 			mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
 			mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
 		}