Re: [Qemu-devel] post-copy is broken?

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Li, Liang Z (liang.z.li@intel.com) wrote:
> > * Li, Liang Z (liang.z.li@intel.com) wrote:
> > > > > > > I've run it directly, setting relevant QTEST_QEMU_BINARY.
> > > > > >
> > > > > > Interesting; it's failing reliably for me - but only with a
> > > > > > reasonably freshly booted machine (so that the pages get THPd).
> > > > >
> > > > > The same here. Freshly booted machine with 64GiB ram. I've checked
> > > > > /proc/vmstat: huge pages were allocated
> > > >
> > > > Thanks for testing.
> > > >
> > > > Damn; this is confusing now.  I've got a RHEL7 box with 4.6.0-rc3 on
> > > > where it works, and a fedora24 VM where it fails (the f24 VM is
> > > > where I did the bisect so it works fine with the older kernel on the f24
> > userspace in that VM).
> > > >
> > > > So lets see:
> > > >    works: Kirill's (64GB machine)
> > > >           Dave's RHEL7 host (24GB RAM, dual xeon, RHEL7 userspace
> > > > and kernel
> > > > config)
> > > >    fails: Dave's f24 VM (4GB RAM, 4 vcpus VM on my laptop24
> > > > userspace and kernel config)
> > > >
> > > > So it's any of userspace, kernel config, machine hardware or hmm.
> > > >
> > > > My f24 box has transparent_hugepage_madvise, where my rhel7 has
> > > > transparent_hugepage_always (but still works if I flip it to madvise
> > > > at run time).  I'll try and get the configs closer together.
> > > >
> > > > Liang Li: Can you run my test on your setup which fails the migrate
> > > > and tell me what your userspace is?
> > > >
> > > > (If you've not built my test yet, you might find you need to add a :
> > > >    tests/postcopy-test$(EXESUF): tests/postcopy-test.o
> > > >
> > > >   to the tests/Makefile)
> > > >
> > >
> > > Hi Dave,
> > >
> > >   How to build and run you test? I didn't do that before.
> > 
> > Apply the code in:
> > http://lists.gnu.org/archive/html/qemu-devel/2016-04/msg02138.html
> > 
> > fix the:
> > +            if ( ((b + 1) % 255) == last_byte && !hit_edge) {
> > to:
> > +            if ( ((b + 1) % 256) == last_byte && !hit_edge) {
> > 
> > to tests/Makefile
> >    tests/postcopy-test$(EXESUF): tests/postcopy-test.o
> > 
> > and do a:
> >     make check
> > 
> > in qemu.
> > Then you can rerun the test with:
> >     QTEST_QEMU_BINARY=path/to/qemu-system-x86_64 ./tests/postcopy-
> > test
> > 
> > if it works, reboot and check it still works from a fresh boot.
> > 
> > Can you describe the system which your full test failed on? What distro on
> > the host? What type of host was it tested on?
> > 
> > Dave
> > 
> 
> 
> Thanks, Dave
> 
> The host is CenOS7, its original kernel is 3.10.0-327.el7.x86_64 (CentOS 7.1?),
> The hardware platform is HSW-EP with 64GB RAM.

OK, so your test fails on real hardware; my guess is that my test will work
on there.
Can you try your test with THP disabled on the host:

echo never > /sys/kernel/mm/transparent_hugepage/enabled

Dave

> 
> 
> > >
> > > Thanks!
> > > Liang
> > >
> > > >
> > > > Dave
> > > > >
> > > > > --
> > > > >  Kirill A. Shutemov
> > > > --
> > > > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> > --
> > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK