This patch series introduces MEMORY_DEVICE_COHERENT, a type of memory owned by a device that can be mapped into CPU page tables like MEMORY_DEVICE_GENERIC and can also be migrated like MEMORY_DEVICE_PRIVATE.
Christoph, the suggestion to incorporate Ralph Campbell’s refcount cleanup patch into our hardware page migration patchset originally came from you, but it proved impractical to do things in that order because the refcount cleanup introduced a bug with wide ranging structural implications. Instead, we amended Ralph’s patch so that it could be applied after merging the migration work. As we saw from the recent discussion, merging the refcount work is going to take some time and cooperation between multiple development groups, while the migration work is ready now and is needed now. So we propose to merge this patchset first and continue to work with Ralph and others to merge the refcount cleanup separately, when it is ready.
This patch series is mostly self-contained except for a few places where it needs to update other subsystems to handle the new memory type.
System stability and performance are not affected according to our ongoing testing, including xfstests.
How it works: The system BIOS advertises the GPU device memory (aka VRAM) as SPM (special purpose memory) in the UEFI system address map.
The amdgpu driver registers the memory with devmap as MEMORY_DEVICE_COHERENT using devm_memremap_pages. The initial user for this hardware page migration capability is the Frontier supercomputer project. This functionality is not AMD-specific. We expect other GPU vendors to find this functionality useful, and possibly other hardware types in the future.
Our test nodes in the lab are similar to the Frontier configuration, with .5 TB of system memory plus 256 GB of device memory split across 4 GPUs, all in a single coherent address space. Page migration is expected to improve application efficiency significantly. We will report empirical results as they become available.
We extended hmm_test to cover migration of MEMORY_DEVICE_COHERENT. This patch set builds on HMM and our SVM memory manager already merged in 5.15.
v2: - test_hmm is now able to create private and coherent device mirror instances in the same driver probe. This adds more usability to the hmm test by not having to remove the kernel module for each device type test (private/coherent type). This is done by passing the module parameters spm_addr_dev0 & spm_addr_dev1. In this case, it will create four instances of device_mirror. The first two correspond to private device type, the last two to coherent type. Then, they can be easily accessed from user space through /dev/hmm_mirror<num_device>. Usually num_device 0 and 1 are for private, and 2 and 3 for coherent types.
- Coherent device type pages at gup are now migrated back to system memory if they have been long term pinned (FOLL_LONGTERM). The reason is these pages could eventually interfere with their own device memory manager. A new hmm_gup_test has been added to the hmm-test to test this functionality. It makes use of the gup_test module to long term pin user pages that have been migrate to device memory first.
- Other patch corrections made by Felix, Alistair and Christoph.
v3: - Based on last v2 feedback we got from Alistair, we've decided to remove migration logic for FOLL_LONGTERM coherent device type pages at gup for now. Ideally, this should be done through the kernel mm, instead of calling the device driver to do it. Currently, there's no support for migrating device pages based on pfn, mainly because migrate_pages() relies on pages being LRU pages. Alistair mentioned, he has started to work on adding this migrate device pages logic. For now, we fail on get_user_pages call with FOLL_LONGTERM for DEVICE_COHERENT pages.
- Also, hmm_gup_test has been removed from hmm-test. We plan to include it again after this migration work is ready.
- Addressed Liam Howlett's feedback changes.
v4: - Addressed Alistair Popple's last v3 feedback.
- Use the same system entry path for coherent device pages at migrate_vma_insert_page.
- Add coherent device type support for try_to_migrate / try_to_migrate_one.
- Include number of coherent device pages successfully migrated back to system at test_hmm. Made the proper changes to hmm-test to read/check this number.
v5: - Rebase on 5.17-rc1. - Addressed Alistair Popple's last v4 feedback.
Alex Sierra (10): mm: add zone device coherent type memory support mm: add device coherent vma selection for memory migration mm/gup: fail get_user_pages for LONGTERM dev coherent type drm/amdkfd: add SPM support for SVM drm/amdkfd: coherent type as sys mem on migration to ram lib: test_hmm add ioctl to get zone device type lib: test_hmm add module param for zone device type lib: add support for device coherent type in test_hmm tools: update hmm-test to support device coherent type tools: update test_hmm script to support SP config
drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 34 ++- include/linux/memremap.h | 8 + include/linux/migrate.h | 1 + include/linux/mm.h | 16 + lib/test_hmm.c | 356 +++++++++++++++++------ lib/test_hmm_uapi.h | 22 +- mm/gup.c | 7 + mm/memcontrol.c | 6 +- mm/memory-failure.c | 8 +- mm/memremap.c | 14 +- mm/migrate.c | 55 ++-- mm/rmap.c | 5 +- tools/testing/selftests/vm/hmm-tests.c | 123 ++++++-- tools/testing/selftests/vm/test_hmm.sh | 24 +- 14 files changed, 519 insertions(+), 160 deletions(-)