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

[Li, Liang Z]

> > > > > > > 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
> 

If the THP is disabled, no fails.
And your test was always passed, even when  real post-copy was failed. 

In my env, the output of 
'cat /sys/kernel/mm/transparent_hugepage/enabled'  is:

 [always] ...

Liang

> Dave
> 
> >
> >
> > > >
> > > > Thanks!
> > > > Liang
> > > >
> > > > >
> > > > > Dave
> > > > > >
> > > > > > --
> > > > > >  Kirill A. Shutemov
> > > > > --
> > > > > Dr. David Alan Gilbert / address@hidden / Manchester, UK
> > > --
> > > Dr. David Alan Gilbert / address@hidden / Manchester, UK
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK