Hey, > Okay, so clearly this needs a kernel side NVMe specific allocator > and locking so users don't step on each other.. Yup, ideally. That's why device dax isn't ideal for this application: it doesn't provide any way to prevent users from stepping on each other. > Or as Christoph says some kind of general mechanism to get these > bounce buffers.. Yeah, I imagine a general allocate from BAR/region system would be very useful. > Ah, I see. > > As a first draft I'd stick with some kind of API built into the > /dev/nvmeX that backs the filesystem. The user app would fstat the > target file, open /dev/block/MAJOR(st_dev):MINOR(st_dev), do some > ioctl to get a CMB mmap, and then proceed from there.. > > When that is all working kernel-side, it would make sense to look at a > more general mechanism that could be used unprivileged?? That makes a lot of sense to me. I suggested mmapping the char device because it's really easy, but I can see that an ioctl on the block device does seem more general and device agnostic. > This is similar to the GPU issues too.. On NVMe you don't need to pin > the pages, you just need to lock that VMA so it doesn't get freed from > the NVMe CMB allocator while the IO is running... > Probably in the long run the get_user_pages is going to have to be > pushed down into drivers.. Future MMU coherent IO hardware also does > not need the pinning or other overheads. Yup. Yup. Logan -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
