Device coherent pages represent memory on a coherently attached device such as a GPU which is usually under the control of a driver. These pages should not be pinned as the driver needs to be able to move pages as required. Currently this is enforced by failing any attempt to pin a device coherent page.
A similar problem exists for ZONE_MOVABLE pages. In that case though the pages are migrated instead of causing failure. There is no reason the kernel can't migrate device coherent pages so this series implements migration for device coherent pages so the same strategy of migrate and pin can be used.
This series depends on the series "Add MEMORY_DEVICE_COHERENT for coherent device memory mapping"[1] and should apply cleanly on top of that.
[1] - https://lore.kernel.org/linux-mm/20220128200825.8623-1-alex.sierra@amd.com/
Alex Sierra (1): tools: add hmm gup test for long term pinned device pages
Alistair Popple (2): migrate.c: Remove vma check in migrate_vma_setup() mm/gup.c: Migrate device coherent pages when pinning instead of failing
mm/gup.c | 105 +++++++++++++++++++++++--- mm/migrate.c | 34 ++++---- tools/testing/selftests/vm/Makefile | 2 +- tools/testing/selftests/vm/hmm-tests.c | 81 ++++++++++++++++++++- 4 files changed, 194 insertions(+), 28 deletions(-)