On Wed, Nov 15, 2017 at 7:23 PM, chetan L <loke.che...@gmail.com> wrote: > CC'ing : linux-accelerat...@vger.kernel.org >
Sorry, CC'ing the correct list this time: linux-accelerat...@lists.ozlabs.org > On Wed, Nov 15, 2017 at 6:44 PM, Jerome Glisse <jgli...@redhat.com> wrote: >> On Wed, Nov 15, 2017 at 06:10:08PM -0800, chet l wrote: >>> >> You may think it as a CCIX device or CAPI device. >>> >> The requirement is eliminate any extra copy. >>> >> A typical usecase/requirement is malloc() and madvise() allocate from >>> >> device memory, then CPU write data to device memory directly and >>> >> trigger device to read the data/do calculation. >>> > >>> > I suggest you rely on the device driver userspace API to do a migration >>> > after malloc >>> > then. Something like: >>> > ptr = malloc(size); >>> > my_device_migrate(ptr, size); >>> > >>> > Which would call an ioctl of the device driver which itself would migrate >>> > memory or >>> > allocate device memory for the range if pointer return by malloc is not >>> > yet back by >>> > any pages. >>> > >>> >>> So for CCIX, I don't think there is going to be an inline device >>> driver that would allocate any memory for you. The expansion memory >>> will become part of the system memory as part of the boot process. So, >>> if the host DDR is 256GB and the CCIX expansion memory is 4GB, the >>> total system mem will be 260GB. >>> >>> Assume that the 'mm' is taught to mark/anoint the ZONE_DEVICE(or >>> ZONE_XXX) range from 256 to 260 GB. Then, for kmalloc it(mm) won't use >>> the ZONE_DEV range. But for a malloc, it will/can use that range. >> >> HMM zone device memory would work with that, you just need to teach the >> platform to identify this memory zone and not hotplug it. Again you >> should rely on specific device driver API to allocate this memory. >> > > @Jerome - a new linux-accelerator's list has just been created. I have > CC'd that list since we have overlapping interests w.r.t CCIX. > > I cannot comment on surprise add/remove as of now ... will cross the > bridge later. > > >>> > There has been several discussions already about >>> > madvise/mbind/set_mempolicy/ >>> > move_pages and at this time i don't think we want to add or change any of >>> > them to >>> > understand device memory. My personal opinion is that we first need to >>> > have enough >>> >>> We will visit these APIs when we are more closer to building exotic >>> CCIX devices. And the plan is to present/express the CCIX proximity >>> attributes just like a NUMA node-proximity attribute today. That way >>> there would be minimal disruptions to the existing OS ecosystem. >> >> NUMA have been rejected previously see CDM/CAPI threads. So i don't see >> it being accepted for CCIX either. My belief is that we want to hide this >> inside device driver and only once we see multiple devices all doing the >> same kind of thing we should move toward building something generic that >> catter to CCIX devices. > > > Thanks for pointing out the NUMA thingy. I will visit the CDM/CAPI > threads to understand what was discussed before commenting further. >
