On Thu, Feb 14, 2013 at 01:52:34PM -0800, Andrew Morton wrote: > 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. I will go look at those now. I am not familiar with them as they went in during my "dark period" where I was working on system controller functionality and not paying attention to kernel activity. > > > > 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? Yes, for the extended virtual and physical address space and for the weird page sizes. Thanks, Robin -- 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>