* Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > On Tue, Apr 08, 2014 at 05:46:52PM +0100, Mel Gorman wrote: > > Someone will ask why automatic NUMA balancing hints do not use "real" > > PROT_NONE but as it would need VMA information to do that on all > > architectures it would mean that VMA-fixups would be required when marking > > PTEs for NUMA hinting faults so would be expensive. > > Like this: > > https://lkml.org/lkml/2012/11/13/431 > > That used the generic PROT_NONE infrastructure and compared, on fault, > the page protection bits against the vma->vm_page_prot bits? > > So the objection to that approach was the vma-> dereference in > pte_numa() ? I think the real underlying objection was that PTE_NUMA was the last leftover from AutoNUMA, and removing it would have made it not a 'compromise' patch set between 'AutoNUMA' and 'sched/numa', but would have made the sched/numa approach 'win' by and large. The whole 'losing face' annoyance that plagues all of us (me included). I didn't feel it was important to the general logic of adding access pattern aware NUMA placement logic to the scheduler, and I obviously could not ignore the NAKs from various mm folks insisting on PTE_NUMA, so I conceded that point and Mel built on that approach as well. Nice it's being cleaned up, and I'm pretty happy about how NUMA balancing ended up looking like. Thanks, Ingo -- 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>