diff mbox series

[v7,04/14] mm: add device coherent vma selection for memory migration

Message ID 20220629035426.20013-5-alex.sierra@amd.com
State Not Applicable
Headers show
Series Add MEMORY_DEVICE_COHERENT for coherent device memory mapping | expand

Commit Message

Sierra Guiza, Alejandro (Alex) June 29, 2022, 3:54 a.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 <alex.sierra@amd.com>
Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Alistair Poppple <apopple@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/migrate.h |  1 +
 mm/migrate_device.c     | 12 +++++++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

Comments

David Hildenbrand June 30, 2022, 10:04 a.m. UTC | #1 
On 29.06.22 05:54, Alex Sierra wrote:
> 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 <alex.sierra@amd.com>
> Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
> Reviewed-by: Alistair Poppple <apopple@nvidia.com>
> Signed-off-by: Christoph Hellwig <hch@lst.de>


I'm not too familiar with this code, please excuse my naive questions:

> @@ -148,15 +148,21 @@ 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))
> -				goto next;

Why not exclude MIGRATE_VMA_SELECT_DEVICE_PRIVATE here? IIRC that would
have happened before this change.


>  			pfn = pte_pfn(pte);
> -			if (is_zero_pfn(pfn)) {
> +			if (is_zero_pfn(pfn) &&
> +			    (migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) {
>  				mpfn = MIGRATE_PFN_MIGRATE;
>  				migrate->cpages++;
>  				goto next;
>  			}
>  			page = vm_normal_page(migrate->vma, addr, pte);
> +			if (page && !is_zone_device_page(page) &&

I'm wondering if that check logically belongs into patch #2.

> +			    !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
> +				goto next;
> +			else if (page && is_device_coherent_page(page) &&
> +			    (!(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_COHERENT) ||
> +			     page->pgmap->owner != migrate->pgmap_owner))


In general LGTM
Alistair Popple June 30, 2022, 11:44 a.m. UTC | #2 
David Hildenbrand <david@redhat.com> writes:

> On 29.06.22 05:54, Alex Sierra wrote:
>> 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 <alex.sierra@amd.com>
>> Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
>> Reviewed-by: Alistair Poppple <apopple@nvidia.com>
>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>
>
> I'm not too familiar with this code, please excuse my naive questions:
>
>> @@ -148,15 +148,21 @@ 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))
>> -				goto next;
>
> Why not exclude MIGRATE_VMA_SELECT_DEVICE_PRIVATE here? IIRC that would
> have happened before this change.

I might be missing something as I don't quite follow - this path is for
normal system pages so we only want to skip selecting them if
MIGRATE_VMA_SELECT_SYSTEM or MIGRATE_VMA_SELECT_DEVICE_COHERENT aren't
set.

Note that MIGRATE_VMA_SELECT_DEVICE_PRIVATE doesn't apply here because
we already know it's not a device private page by virtue of
pte_present(pte) == True.

>>  			pfn = pte_pfn(pte);
>> -			if (is_zero_pfn(pfn)) {
>> +			if (is_zero_pfn(pfn) &&
>> +			    (migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) {
>>  				mpfn = MIGRATE_PFN_MIGRATE;
>>  				migrate->cpages++;
>>  				goto next;
>>  			}
>>  			page = vm_normal_page(migrate->vma, addr, pte);
>> +			if (page && !is_zone_device_page(page) &&
>
> I'm wondering if that check logically belongs into patch #2.

I don't think so as it would break functionality until the below
conditionals are added - we explicitly don't want to skip
is_zone_device_page(page) == False here because that is the pages we are
trying to select.

You could add in this:

>> +			    !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))

But then in patch 2 we know this can never be true because we've already
checked for !MIGRATE_VMA_SELECT_SYSTEM there.

>> +				goto next;
>> +			else if (page && is_device_coherent_page(page) &&
>> +			    (!(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_COHERENT) ||
>> +			     page->pgmap->owner != migrate->pgmap_owner))
>
>
> In general LGTM
David Hildenbrand June 30, 2022, 8:56 p.m. UTC | #3 
On 30.06.22 13:44, Alistair Popple wrote:
> 
> David Hildenbrand <david@redhat.com> writes:
> 
>> On 29.06.22 05:54, Alex Sierra wrote:
>>> 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 <alex.sierra@amd.com>
>>> Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
>>> Reviewed-by: Alistair Poppple <apopple@nvidia.com>
>>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>>
>>
>> I'm not too familiar with this code, please excuse my naive questions:
>>
>>> @@ -148,15 +148,21 @@ 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))
>>> -				goto next;
>>
>> Why not exclude MIGRATE_VMA_SELECT_DEVICE_PRIVATE here? IIRC that would
>> have happened before this change.
> 
> I might be missing something as I don't quite follow - this path is for
> normal system pages so we only want to skip selecting them if
> MIGRATE_VMA_SELECT_SYSTEM or MIGRATE_VMA_SELECT_DEVICE_COHERENT aren't
> set.
> 
> Note that MIGRATE_VMA_SELECT_DEVICE_PRIVATE doesn't apply here because
> we already know it's not a device private page by virtue of
> pte_present(pte) == True.

Ah, stupid me, pte_present(pte) is the key.

> 
>>>  			pfn = pte_pfn(pte);
>>> -			if (is_zero_pfn(pfn)) {
>>> +			if (is_zero_pfn(pfn) &&
>>> +			    (migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) {
>>>  				mpfn = MIGRATE_PFN_MIGRATE;
>>>  				migrate->cpages++;
>>>  				goto next;
>>>  			}
>>>  			page = vm_normal_page(migrate->vma, addr, pte);
>>> +			if (page && !is_zone_device_page(page) &&
>>
>> I'm wondering if that check logically belongs into patch #2.
> 
> I don't think so as it would break functionality until the below
> conditionals are added - we explicitly don't want to skip
> is_zone_device_page(page) == False here because that is the pages we are
> trying to select.
> 
> You could add in this:
> 
>>> +			    !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
> 
> But then in patch 2 we know this can never be true because we've already
> checked for !MIGRATE_VMA_SELECT_SYSTEM there.


Ah, okay, thanks

Reviewed-by: David Hildenbrand <david@redhat.com>
diff mbox series

Patch

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 069a89e847f3..b84908debe5c 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -148,6 +148,7 @@  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_device.c b/mm/migrate_device.c
index a4847ad65da3..18bc6483f63a 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -148,15 +148,21 @@  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))
-				goto next;
 			pfn = pte_pfn(pte);
-			if (is_zero_pfn(pfn)) {
+			if (is_zero_pfn(pfn) &&
+			    (migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) {
 				mpfn = MIGRATE_PFN_MIGRATE;
 				migrate->cpages++;
 				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;
+			else 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;
 		}