On Tue, May 27, 2014 at 2:54 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > On Tue, May 27, 2014 at 12:29:09PM +0200, Peter Zijlstra wrote: >> On Tue, May 27, 2014 at 12:49:08AM +0400, Konstantin Khlebnikov wrote: >> > Another suggestion. VM_RESERVED is stronger than VM_LOCKED and extends >> > its functionality. >> > Maybe it's easier to add VM_DONTMIGRATE and use it together with VM_LOCKED. >> > This will make accounting easier. No? >> >> I prefer the PINNED name because the not being able to migrate is only >> one of the desired effects of it, not the primary effect. We're really >> looking to keep physical pages in place and preserve mappings. Ah, I just mixed it up. >> >> The -rt people for example really want to avoid faults (even minor >> faults), and DONTMIGRATE would still allow unmapping. >> >> Maybe always setting VM_PINNED and VM_LOCKED together is easier, I >> hadn't considered that. The first thing that came to mind is that that >> might make the fork() semantics difficult, but maybe it works out. >> >> And while we're on the subject, my patch preserves PINNED over fork() >> but maybe we don't actually need that either. > > So pinned_vm is userspace exposed, which means we have to maintain the > individual counts, and doing the fully orthogonal accounting is 'easier' > than trying to get the boundary cases right. > > That is, if we have a program that does mlockall() and then does the IB > ioctl() to 'pin' a region, we'd have to make mm_mpin() do munlock() > after it splits the vma, and then do the pinned accounting. > > Also, we'll have lost the LOCKED state and unless MCL_FUTURE was used, > we don't know what to restore the vma to on mm_munpin(). > > So while the accounting looks tricky, it has simpler semantics. What if VM_PINNED will require VM_LOCKED? I.e. user must mlock it before pining and cannot munlock vma while it's pinned. -- 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>