On Tue, 12 Oct 2021 12:12:35 -0500 Alex Sierra <alex.sierra@xxxxxxx> wrote: > 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. > With MEMORY_DEVICE_COHERENT, we isolate the new memory type from other > subsystems as far as possible, though there are some small changes to > other subsystems such as filesystem DAX, to handle the new memory type > appropriately. > > We use ZONE_DEVICE for this instead of NUMA so that the amdgpu > allocator can manage it without conflicting with core mm for non-unified > memory use cases. > > 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 will be > the Frontier supercomputer project. To what other uses will this infrastructure be put? Because I must ask: if this feature is for one single computer which presumably has a custom kernel, why add it to mainline Linux? > Our nodes in the lab have .5 TB of > system memory plus 256 GB of device memory split across 4 GPUs, all in > the same coherent address space. Page migration is expected to improve > application efficiency significantly. We will report empirical results > as they become available. > > This includes patches originally by Ralph Campbell to change ZONE_DEVICE > reference counting as requested in previous reviews of this patch series > (see https://patchwork.freedesktop.org/series/90706/). 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 5.14. > We would like to complete review and merge this migration patchset for > 5.16.
