On 04/08/2019 09:33 AM, Ira Weiny wrote: > On Sun, Apr 07, 2019 at 03:11:00PM -0700, Dan Williams wrote: >> On Thu, Apr 4, 2019 at 2:47 AM Robin Murphy <robin.murphy@xxxxxxx> wrote: >>> >>> On 04/04/2019 06:04, Dan Williams wrote: >>>> On Wed, Apr 3, 2019 at 9:42 PM Anshuman Khandual >>>> <anshuman.khandual@xxxxxxx> wrote: >>>>> >>>>> >>>>> >>>>> On 04/03/2019 07:28 PM, Robin Murphy wrote: >>>>>> [ +Dan, Jerome ] >>>>>> >>>>>> On 03/04/2019 05:30, Anshuman Khandual wrote: >>>>>>> Arch implementation for functions which create or destroy vmemmap mapping >>>>>>> (vmemmap_populate, vmemmap_free) can comprehend and allocate from inside >>>>>>> device memory range through driver provided vmem_altmap structure which >>>>>>> fulfils all requirements to enable ZONE_DEVICE on the platform. Hence just >>>>>> >>>>>> ZONE_DEVICE is about more than just altmap support, no? >>>>> >>>>> Hot plugging the memory into a dev->numa_node's ZONE_DEVICE and initializing the >>>>> struct pages for it has stand alone and self contained use case. The driver could >>>>> just want to manage the memory itself but with struct pages either in the RAM or >>>>> in the device memory range through struct vmem_altmap. The driver may not choose >>>>> to opt for HMM, FS DAX, P2PDMA (use cases of ZONE_DEVICE) where it may have to >>>>> map these pages into any user pagetable which would necessitate support for >>>>> pte|pmd|pud_devmap. >>>> >>>> What's left for ZONE_DEVICE if none of the above cases are used? >>>> >>>>> Though I am still working towards getting HMM, FS DAX, P2PDMA enabled on arm64, >>>>> IMHO ZONE_DEVICE is self contained and can be evaluated in itself. >>>> >>>> I'm not convinced. What's the specific use case. >>> >>> The fundamental "roadmap" reason we've been doing this is to enable >>> further NVDIMM/pmem development (libpmem/Qemu/etc.) on arm64. The fact >>> that ZONE_DEVICE immediately opens the door to the various other stuff >>> that the CCIX folks have interest in is a definite bonus, so it would >>> certainly be preferable to get arm64 on par with the current state of >>> things rather than try to subdivide the scope further. >>> >>> I started working on this from the ZONE_DEVICE end, but got bogged down >>> in trying to replace my copied-from-s390 dummy hot-remove implementation >>> with something proper. Anshuman has stepped in to help with hot-remove >>> (since we also have cloud folks wanting that for its own sake), so is >>> effectively coming at the problem from the opposite direction, and I'll >>> be the first to admit that we've not managed the greatest job of meeting >>> in the middle and coordinating our upstream story; sorry about that :) >>> >>> Let me freshen up my devmap patches and post them properly, since that >>> discussion doesn't have to happen in the context of hot-remove; they're >>> effectively just parallel dependencies for ZONE_DEVICE. >> >> Sounds good. It's also worth noting that Ira's recent patches for >> supporting get_user_pages_fast() for "longterm" pins relies on >> PTE_DEVMAP to determine when fast-GUP is safe to proceed, or whether >> it needs to fall back to slow-GUP. So it really is the case that >> "devmap" support is an assumption for ZONE_DEVICE. > > Could you cc me on the patches when you post? Sure will do.
