On Thu, 14 Feb 2013 15:35:12 -0600 Robin Holt <holt@xxxxxxx> wrote: > I am open to suggestions. Can you suggest existing kernel functionality > that allows one task to map another virtual address space into their > va space to allow userland-to-userland copies without system calls? > If there is functionality that has been introduced in the last couple > years, I could very well have missed it as I have been fairly heads-down > on other things for some time. That's conceptually very similar to mm/process_vm_access.c. process_vm_readv/writev do kernel-based copying rather than a direct mmap. > > To what extent is all this specific to SGI hardware characteristics? > > SGI's hardware allows two things, a vastly larger virtual address space > and the ability to access memory in other system images on the same numa > fabric which are beyond the processsors physical addressing capabilities. > > I am fairly sure Cray has taken an older version of XPMEM and stripped > out a bunch of SGI specific bits and implemented it on their hardware. > > > > The above, of course, is an oversimplification, but should give you and > > > idea of the big picture design goals. > > > > > > Does any of this make sense? Do you see areas where you think we should > > > extend regular mm functionality to include these functions? > > > > > > How would you like me to proceed? > > > > I'm obviously on first base here, but overall approach: > > > > - Is the top-level feature useful to general Linux users? Perhaps > > after suitable generalisations (aka dumbing down :)) > > I am not sure how useful it is. I know IBM has tried in the past to > get a similar feature introduced. I believe they settled on a ptrace > extension to do direct user-to-user copies from within the kernel. process_vm_readv/writev is from Christopher Yeoh@IBM. > > - Even if the answer to that is "no", should we maintain the feature > > in-tree rather than out-of-tree? > > Not sure on the second one, but I believe Linus' objection is security and > I can certainly understand that. Right now, SGI's xpmem implementation > enforces that all jobs in the task need to have the same UID. There is > no exception for root or and administrator. I'd have thought that the security processing of a direct map would be identical to those in process_vm_readv/writev? If we were to add a general map-this-into-that facility which is available to and runs adequately on our typical machines, I assume your systems would need some SGI-specific augmentation? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>