Speakers
Description
The Device and Specific Purpose Memory Microconference is proposed as a space to discuss topics that cross MM, Virtualization, and Memory device-driver boundaries. Beyond CXL this includes software methods for device-coherent memory via ZONE_DEVICE, physical memory pooling / sharing, and specific purpose memory application ABIs like device-dax, hugetlbfs, and guest_memfd. Some suggested topic areas include, but not limited to:
NUMA vs Specific Purpose Memory challenges
Core-MM services vs page allocator isolation
CXL use case challenges
Hotness Tracking and Migration Offloads
ZONE_DEVICE future for Accelerator Memory
ZONE_DEVICE future for CXL Memory Expansion
PMEM, NVDIMM, and DAX "legacy" challenges
Memory hotplug vs Device Memory
Memory RAS and repair gaps and challenges
Dynamic Capacity Device ABI (sparse memfd?)
Confidential Memory challenges
DMABUF beyond DRM use cases
virtiomem and virtiofs vs DAX and CXL challenges
Peer-to-peer DMA challenges
CXL Memory Pool Management
Device Memory testing
Why not the MM uConf for these topics? One of the observations from MM track at LSF/MM/BPF is that there is consistently an overflow of Device Memory topics that are of key interest to Memory device-driver developers, but lower priority to core MM developers.
Key Attendees:
Rajneesh Bhardwaj
Terry Bowman
Davidlohr Bueso
John Groves
Jason Gunthorpe
David Hildenbrand
John Hubbard
Alistair Popple
Gregory Price
Contingent or unknown travel availability:
Jonathan Cameron
Dave Jiang
David Rientjes
Ira Weiny
Progress made on topics discussed at 2024 Plumbers:
Merged: CXL EDAC support for Memory Repair: http://lore.kernel.org/20250521124749.817-1-shiju.jose@huawei.com
Launched: CXL Management Library: https://github.com/computexpresslink/libcxlmi
Patches Available: FAMFS over FUSE: http://lore.kernel.org/20250703185032.46568-1-john@groves.net
Patches Available: Dynamic Capacity: http://lore.kernel.org/20250413-dcd-type2-upstream-v9-0-1d4911a0b365@intel.com
Patches Available: Type-2 CXL Accelerators: http://lore.kernel.org/20250624141355.269056-1-alejandro.lucero-palau@amd.com
"Device Memory" Background:
"Device Memory" is a catch-all term for the collection of platform
technologies that add memory to a system outside of the typical "System RAM" default pool. Compute Express Link (CXL), a coherent interconnect that allows memory and caching-agent expansion over PCIe electricals, is one such technology. GPU/AI accelerators with hardware coherent memory, or software coherent memory (ZONE_DEVICE::DEVICE_PRIVATE), are another example technology.
In the Memory Management track of the 2025 LSF/MM/BPF Summit it became clear that CXL is one of a class of technologies putting pressure on traditional NUMA memory policy. While solutions like
memory-interleave-sysfs and device-dax mitigate some of the issues there are still lingering concerns about memory of a certain performance class leaking into allocations that assume "default memory pool" performance.
The problem is how to keep Device / Specific Purpose memory contained to its specific consumers while also offering typical core-mm services. Solutions to that problem potentially intersect mechanisms like numactl, hugetlbfs, memfd, and guest_memfd. For example, guest_memfd is a kind of specific-purpose memory allocator.