https://github.com/Overv/vramfs

Oh, it’s a user space (FUSE) driver. I was rather hoping it was an out-of-tree Linux kernel driver, since using FUSE will: 1) always pass back to userspace, which costs performance, and 2) destroys any possibility of DMA-enabled memory operations (DPDK is a possible exception). I suppose if the only objective was to store files in VRAM, this does technically meet that, but it’s leaving quite a lot on the table, IMO.

If this were a kernel module, the filesystem performance would presumably improve, limited by how the VRAM is exposed by OpenCL (ie very fast if it’s just all mapped into PCIe). And if it was basically offering VRAM as PCIe memory, then this potentially means the VRAM can be used for certain RAM niche cases, like hugepages: some applications need large quantities of memory, plus a guarantee that it won’t be evicted from RAM, and whose physical addresses can be resolved from userspace (eg DPDK, high-performance compute). If such a driver could offer special hugepages which are backed by VRAM, then those application could benefit.

And at that point, on systems where the PCIe address space is unified with the system address space (eg x86), then it’s entirely plausible to use VRAM as if it were hot-insertable memory, because both RAM and VRAM would occupy known regions within the system memory address space, and the existing MMU would control which processes can access what parts of PCIe-mapped-VRAM.

Is it worth re-engineering the Linux kernel memory subsystem to support RAM over PCIe? Uh, who knows. Though I’ve always like the thought of DDR on PCIe cards. All technologies are doomed to reinvent PCIe, I think, said someone from Level1Techs.