On Fri, Feb 05, 2021 at 04:53:04PM +0100, Daniel Vetter wrote: > On Fri, Feb 05, 2021 at 11:43:19AM -0400, Jason Gunthorpe wrote: > > On Fri, Feb 05, 2021 at 04:39:47PM +0100, Daniel Vetter wrote: > > > > > > And again, for slightly older hardware, without pinning to VRAM there is > > > > no way to use this solution here for peer-to-peer. So I'm glad to see that > > > > so far you're not ruling out the pinning option. > > > > > > Since HMM and ZONE_DEVICE came up, I'm kinda tempted to make ZONE_DEVICE > > > ZONE_MOVEABLE (at least if you don't have a pinned vram contigent in your > > > cgroups) or something like that, so we could benefit from the work to make > > > sure pin_user_pages and all these never end up in there? > > > > ZONE_DEVICE should already not be returned from GUP. > > > > I've understood in the hmm casse the idea was a CPU touch of some > > ZONE_DEVICE pages would trigger a migration to CPU memory, GUP would > > want to follow the same logic, presumably it comes for free with the > > fault handler somehow > > Oh I didn't know this, I thought the proposed p2p direct i/o patches would > just use the fact that underneath ZONE_DEVICE there's "normal" struct > pages. So, if that every happens, it would be some special FOLL_ALLOW_P2P flag to get the behavior. > And so I got worried that maybe also pin_user_pages can creep in. > But I didn't read the patches in full detail: And yes, you might want to say that you can't longterm pin certain kinds of zone_device pages, but if that is the common operating mode then we'd probably never create a FOLL_ALLOW_P2P > But if you're saying that this all needs specific code and all the gup/pup > code we have is excluded, I think we can make sure that we're not ever > building features that requiring time-unlimited pinning of > ZONE_DEVICE. Well, it is certainly a useful idea of some uses of ZONE_DEVICE, GPU vram is not the whole world. Jason
