On Tue, Oct 02, 2018 at 01:29:42PM -0700, David Rientjes wrote: > On Tue, 2 Oct 2018, Michal Hocko wrote: > > > On Wed 26-09-18 08:06:24, Michal Hocko wrote: > > > On Tue 25-09-18 15:04:06, Andrew Morton wrote: > > > > On Tue, 25 Sep 2018 14:45:19 -0700 (PDT) David Rientjes <rientjes@xxxxxxxxxx> wrote: > > > > > > > > > > > It is also used in > > > > > > > automated testing to ensure that vmas get disabled for thp appropriately > > > > > > > and we used "nh" since that is how PR_SET_THP_DISABLE previously enforced > > > > > > > this, and those tests now break. > > > > > > > > > > > > This sounds like a bit of an abuse to me. It shows how an internal > > > > > > implementation detail leaks out to the userspace which is something we > > > > > > should try to avoid. > > > > > > > > > > > > > > > > Well, it's already how this has worked for years before commit > > > > > 1860033237d4 broke it. Changing the implementation in the kernel is fine > > > > > as long as you don't break userspace who relies on what is exported to it > > > > > and is the only way to determine if MADV_NOHUGEPAGE is preventing it from > > > > > being backed by hugepages. > > > > > > > > 1860033237d4 was over a year ago so perhaps we don't need to be > > > > too worried about restoring the old interface. In which case > > > > we have an opportunity to make improvements such as that suggested > > > > by Michal? > > > > > > Yeah, can we add a way to export PR_SET_THP_DISABLE to userspace > > > somehow? E.g. /proc/<pid>/status. It is a process wide thing so > > > reporting it per VMA sounds strange at best. > > > > So how about this? (not tested yet but it should be pretty > > straightforward) > > Umm, prctl(PR_GET_THP_DISABLE)? > ~/git/linux$ git grep PR_GET_THP_DISABLE include/uapi/linux/prctl.h:#define PR_GET_THP_DISABLE 42 kernel/sys.c: case PR_GET_THP_DISABLE: tools/include/uapi/linux/prctl.h:#define PR_GET_THP_DISABLE 42 -- Sincerely yours, Mike.
