On Mon, Oct 20, 2014 at 05:07:02PM -0700, Andy Lutomirski wrote: > On 10/20/2014 02:56 PM, Peter Zijlstra wrote: > > Hi, > > > > I figured I'd give my 2010 speculative fault series another spin: > > > > https://lkml.org/lkml/2010/1/4/257 > > > > Since then I think many of the outstanding issues have changed sufficiently to > > warrant another go. In particular Al Viro's delayed fput seems to have made it > > entirely 'normal' to delay fput(). Lai Jiangshan's SRCU rewrite provided us > > with call_srcu() and my preemptible mmu_gather removed the TLB flushes from > > under the PTL. > > > > The code needs way more attention but builds a kernel and runs the > > micro-benchmark so I figured I'd post it before sinking more time into it. > > > > I realize the micro-bench is about as good as it gets for this series and not > > very realistic otherwise, but I think it does show the potential benefit the > > approach has. > > Does this mean that an entire fault can complete without ever taking > mmap_sem at all? If so, that's a *huge* win. Yep. > I'm a bit concerned about drivers that assume that the vma is unchanged > during .fault processing. In particular, is there a race between .close > and .fault? Would it make sense to add a per-vma rw lock and hold it > during vma modification and .fault calls? VMA granularity contention would be about as bad as mmap_sem for many workloads. But yes, that is one of the things we need to look at, I was _hoping_ that holding the file open would sort most these problems, but I'm sure there plenty 'interesting' cruft left. -- 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>