On Fri, Dec 28, 2018 at 02:36:32PM -0800, David Rientjes wrote: > On Sat, 29 Dec 2018, Kirill A. Shutemov wrote: > > > > Smaps reveals the state of each vma at the moment it is read, not the > > > future, this has always been the case before and after the broken commit; > > > it's not intended to be something that can specify "thp is currently > > > disabled, but if we did prctl(PR_SET_THP_DISABLE, 0), this vma has done > > > madvise(MADV_HUGEPAGE), and we are on a thp enabled == madvise host, so > > > it would be eligible for thp." > > > > The point of CRIU is that it tries to save and re-create the state of the > > process. > > > > With your fix, "nh" in VMA flags can mean two different things: > > - MADV_NOHUGEPAGE was called for the VMA, or > > - prctl(PR_SET_THP_DISABLE) was called for the whole process > > > > Current CRIU code assumes that "nh" means MADV_NOHUGEPAGE. But if it was > > due to prctl(PR_SET_THP_DISABLE) the process state will not be restored > > correctly: all VMAs will be restored with MADV_NOHUGEPAGE and future > > re-enabling THP with prctl(PR_SET_THP_DISABLE) for restored process will > > not have any effect. VMAs stay not eligble for THP. > > > > CRIU's usage of "nh" was created specifically for PR_SET_THP_DISABLE: > > commit 9f61de87768b33d9b187ef71a57262a17276ff3b > > proc_parse: make smaps parsing helpers globally available > > The is_vma_range_fmt and parse_vmflags will be required for detection of > availability of PR_SET_THP_DISABLE prctl > > Acked-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> > Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> > Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxxxxx> > > > That's at > https://github.com/checkpoint-restore/criu/commit/9f61de87768b33d9b187ef71a57262a17276ff3b. > > They are using it for the *exact* same reason that we are. That commit > was merged June 2017 based on the kernel code as it existed prior to the > broken commit in July 2017. > > > Does this not suggest that CRIU is now equally as broken as my userspace? I think it *was* broken in the same way as your userspace. And it was adjusted to the updated kernel by 5480a2a40683. -- Kirill A. Shutemov
