On 05/27/2014 01:11 PM, Konstantin Khlebnikov wrote: > 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. Mlocking makes sense, as pages won't be uselessly scanned on non-evictable LRU, no? (Or maybe I just don't see that something else prevents then from being there already). Anyway I like the idea of playing nicer with compaction etc. > -- > 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> > -- 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>