Hi, On Thu, Nov 20, 2014 at 10:54:29AM +0800, zhanghailiang wrote: > Yes, you are right. This is what i really want, bypass all non-present faults > and only track strict wrprotect faults. ;) > > So, do you plan to support that in the userfault API?
Yes I think it's good idea to support wrprotect/COW faults too. I just wanted to understand if there was any other reason why you needed only wrprotect faults, because the non-present faults didn't look like a big performance concern if they triggered in addition to wrprotect faults, but it's certainly ok to optimize them away so it's fully optimal. All it takes to differentiate the behavior should be one more bit during registration so you can select non-present, wrprotect faults or both. postcopy live migration would select only non-present faults, postcopy live snapshot would select only wrprotect faults, anything like distributed shared memory supporting shared readonly access and exclusive write access, would select both flags. I just sent an (unfortunately) longish but way more detailed email about live snapshotting with userfaultfd but I just wanted to give a shorter answer here too :). Thanks, Andrea
