On 8/15/2021 10:38 AM, Christoph Hellwig wrote:

On Fri, Aug 13, 2021 at 01:31:42AM -0500, Alex Sierra wrote:

quoted

  	migrate.vma = vma;
  	migrate.start = start;
  	migrate.end = end;
-	migrate.flags = MIGRATE_VMA_SELECT_DEVICE_PRIVATE;
  	migrate.pgmap_owner = SVM_ADEV_PGMAP_OWNER(adev);
  
+	if (adev->gmc.xgmi.connected_to_cpu)
+		migrate.flags = MIGRATE_VMA_SELECT_SYSTEM;
+	else
+		migrate.flags = MIGRATE_VMA_SELECT_DEVICE_PRIVATE;

It's been a while since I touched this migrate code, but doesn't this
mean that if the range already contains system memory the migration
now won't do anything? for the connected_to_cpu case?

For above’s condition equal to connected_to_cpu , we’re explicitly 
migrating from
device memory to system memory with device generic type. In this type, 
device PTEs are
present in CPU page table.

During migrate_vma_collect_pmd walk op at migrate_vma_setup call, 
there’s a condition
for present pte that require migrate->flags be set for 
MIGRATE_VMA_SELECT_SYSTEM.
Otherwise, the migration for this entry will be ignored.

Regards,
Alex S.