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. And so I got worried that maybe also pin_user_pages can creep in. But I didn't read the patches in full detail: https://lore.kernel.org/linux-block/20201106170036.18713-12-logang@xxxxxxxxxxxx/ 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. Which I think we want. Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
