On Tue, Jan 5, 2021 at 5:30 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > > On 05.01.21 10:20, Michal Hocko wrote: > > On Mon 04-01-21 15:00:31, Dave Hansen wrote: > >> On 1/4/21 12:11 PM, David Hildenbrand wrote: > >>>> Yeah, it certainly can't be the default, but it *is* useful for > >>>> thing where we know that there are no cache benefits to zeroing > >>>> close to where the memory is allocated. > >>>> > >>>> The trick is opting into it somehow, either in a process or a VMA. > >>>> > >>> The patch set is mostly trying to optimize starting a new process. So > >>> process/vma doesn‘t really work. > >> > >> Let's say you have a system-wide tunable that says: pre-zero pages and > >> keep 10GB of them around. Then, you opt-in a process to being allowed > >> to dip into that pool with a process-wide flag or an madvise() call. > >> You could even have the flag be inherited across execve() if you wanted > >> to have helper apps be able to set the policy and access the pool like > >> how numactl works. > > > > While possible, it sounds quite heavy weight to me. Page allocator would > > have to somehow maintain those pre-zeroed pages. This pool will also > > become a very scarce resource very soon because everybody just want to > > run faster. So this would open many more interesting questions. > > Agreed. > > > > > A global knob with all or nothing sounds like an easier to use and > > maintain solution to me. > > I mean, that brings me back to my original suggestion: just use > hugetlbfs and implement some sort of pre-zeroing there (worker thread, > whatsoever). Most vfio users should already be better of using hugepages. > > It's a "pool of pages" already. Selected users use it. I really don't > see a need to extend the buddy with something like that. > OK, since most people prefer hugetlbfs, I will send another revision for this. Thanks Liang
