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SubjectHow much of a mess does OpenVZ make? ;) Was: What can OpenVZ do?
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On Thu, 2009-02-12 at 14:10 -0800, Andrew Morton wrote:
> On Thu, 12 Feb 2009 13:51:23 -0800
> Dave Hansen <dave@linux.vnet.ibm.com> wrote:
>
> > On Thu, 2009-02-12 at 11:42 -0800, Andrew Morton wrote:
> > > On Thu, 12 Feb 2009 13:30:35 -0600
> > > Matt Mackall <mpm@selenic.com> wrote:
> > >
> > > > On Thu, 2009-02-12 at 10:11 -0800, Dave Hansen wrote:
> > > >
> > > > > > - In bullet-point form, what features are missing, and should be added?
> > > > >
> > > > > * support for more architectures than i386
> > > > > * file descriptors:
> > > > > * sockets (network, AF_UNIX, etc...)
> > > > > * devices files
> > > > > * shmfs, hugetlbfs
> > > > > * epoll
> > > > > * unlinked files
> > > >
> > > > > * Filesystem state
> > > > > * contents of files
> > > > > * mount tree for individual processes
> > > > > * flock
> > > > > * threads and sessions
> > > > > * CPU and NUMA affinity
> > > > > * sys_remap_file_pages()
> > > >
> > > > I think the real questions is: where are the dragons hiding? Some of
> > > > these are known to be hard. And some of them are critical checkpointing
> > > > typical applications. If you have plans or theories for implementing all
> > > > of the above, then great. But this list doesn't really give any sense of
> > > > whether we should be scared of what lurks behind those doors.
> > >
> > > How close has OpenVZ come to implementing all of this? I think the
> > > implementatation is fairly complete?
> >
> > I also believe it is "fairly complete". At least able to be used
> > practically.
> >
> > > If so, perhaps that can be used as a guide. Will the planned feature
> > > have a similar design? If not, how will it differ? To what extent can
> > > we use that implementation as a tool for understanding what this new
> > > implementation will look like?
> >
> > Yes, we can certainly use it as a guide. However, there are some
> > barriers to being able to do that:
> >
> > dave@nimitz:~/kernels/linux-2.6-openvz$ git diff v2.6.27.10... | diffstat | tail -1
> > 628 files changed, 59597 insertions(+), 2927 deletions(-)
> > dave@nimitz:~/kernels/linux-2.6-openvz$ git diff v2.6.27.10... | wc
> > 84887 290855 2308745
> >
> > Unfortunately, the git tree doesn't have that great of a history. It
> > appears that the forward-ports are just applications of huge single
> > patches which then get committed into git. This tree has also
> > historically contained a bunch of stuff not directly related to
> > checkpoint/restart like resource management.
> >
> > We'd be idiots not to take a hard look at what has been done in OpenVZ.
> > But, for the time being, we have absolutely no shortage of things that
> > we know are important and know have to be done. Our largest problem is
> > not finding things to do, but is our large out-of-tree patch that is
> > growing by the day. :(
> >
>
> Well we have a chicken-and-eggish thing. The patchset will keep
> growing until we understand how much of this:
>
> > dave@nimitz:~/kernels/linux-2.6-openvz$ git diff v2.6.27.10... | diffstat | tail -1
> > 628 files changed, 59597 insertions(+), 2927 deletions(-)
>
> we will be committed to if we were to merge the current patchset.

Here's the measurement that Alexey suggested:

dave@nimitz:~/kernels/linux-2.6-openvz$ git diff v2.6.27.10... kernel/cpt/ | diffstat
Makefile | 53 +
cpt_conntrack.c | 365 ++++++++++++
cpt_context.c | 257 ++++++++
cpt_context.h | 215 +++++++
cpt_dump.c | 1250 ++++++++++++++++++++++++++++++++++++++++++
cpt_dump.h | 16
cpt_epoll.c | 113 +++
cpt_exports.c | 13
cpt_files.c | 1626 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
cpt_files.h | 71 ++
cpt_fsmagic.h | 16
cpt_inotify.c | 144 ++++
cpt_kernel.c | 177 ++++++
cpt_kernel.h | 99 +++
cpt_mm.c | 923 +++++++++++++++++++++++++++++++
cpt_mm.h | 35 +
cpt_net.c | 614 ++++++++++++++++++++
cpt_net.h | 7
cpt_obj.c | 162 +++++
cpt_obj.h | 62 ++
cpt_proc.c | 595 ++++++++++++++++++++
cpt_process.c | 1369 ++++++++++++++++++++++++++++++++++++++++++++++
cpt_process.h | 13
cpt_socket.c | 790 ++++++++++++++++++++++++++
cpt_socket.h | 33 +
cpt_socket_in.c | 450 +++++++++++++++
cpt_syscalls.h | 101 +++
cpt_sysvipc.c | 403 +++++++++++++
cpt_tty.c | 215 +++++++
cpt_ubc.c | 132 ++++
cpt_ubc.h | 23
cpt_x8664.S | 67 ++
rst_conntrack.c | 283 +++++++++
rst_context.c | 323 ++++++++++
rst_epoll.c | 169 +++++
rst_files.c | 1648 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
rst_inotify.c | 196 ++++++
rst_mm.c | 1151 +++++++++++++++++++++++++++++++++++++++
rst_net.c | 741 +++++++++++++++++++++++++
rst_proc.c | 580 +++++++++++++++++++
rst_process.c | 1640 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
rst_socket.c | 918 +++++++++++++++++++++++++++++++
rst_socket_in.c | 489 ++++++++++++++++
rst_sysvipc.c | 633 +++++++++++++++++++++
rst_tty.c | 384 +++++++++++++
rst_ubc.c | 131 ++++
rst_undump.c | 1007 ++++++++++++++++++++++++++++++++++
47 files changed, 20702 insertions(+)
One important thing that leaves out is the interaction that this code
has with the rest of the kernel. That's critically important when
considering long-term maintenance, and I'd be curious how the OpenVZ
folks view it.

> Now, we've gone in blind before - most notably on the
> containers/cgroups/namespaces stuff. That hail mary pass worked out
> acceptably, I think. Maybe we got lucky. I thought that
> net-namespaces in particular would never get there, but it did.
>
> That was a very large and quite long-term-important user-visible
> feature.
>
> checkpoint/restart/migration is also a long-term-...-feature. But if
> at all possible I do think that we should go into it with our eyes a
> little less shut.

One thing Ingo has asked for that I understand a bit more clearly is a
programmatic statement of what is and is not covered by this current
code. That's certainly one eye-opening activity which I'll get to
immediately.

-- Dave



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