Re: [PATCH v19 for-4.14 00/13] VM forking

From: Tamas K Lengyel <tamas@tklengyel.com>
To: George Dunlap <George.Dunlap@citrix.com>
Cc: Julien Grall <julien@xen.org>, Kevin Tian <kevin.tian@intel.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Tamas K Lengyel <tamas.lengyel@intel.com>,
	Jan Beulich <jbeulich@suse.com>, Wei Liu <wl@xen.org>,
	"paul@xen.org" <paul@xen.org>,
	Andrew Cooper <Andrew.Cooper3@citrix.com>,
	Jun Nakajima <jun.nakajima@intel.com>,
	Ian Jackson <Ian.Jackson@citrix.com>,
	Anthony Perard <anthony.perard@citrix.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [PATCH v19 for-4.14 00/13] VM forking
Date: Mon, 1 Jun 2020 12:37:42 -0600	[thread overview]
Message-ID: <CABfawh=YHA9Lxbto5Qgf_wkSFAR+JxCdWB99iAhCmBgwSwvmVg@mail.gmail.com> (raw)
In-Reply-To: <4017F2B3-BB9B-4E9F-813C-6FE68BA0D568@citrix.com>

On Mon, Jun 1, 2020 at 11:11 AM George Dunlap <George.Dunlap@citrix.com> wrote:
>
>
>
> > On Jun 1, 2020, at 4:07 PM, Paul Durrant <xadimgnik@gmail.com> wrote:
> >
> >> -----Original Message-----
> >> From: Xen-devel <xen-devel-bounces@lists.xenproject.org> On Behalf Of Tamas K Lengyel
> >> Sent: 01 June 2020 14:22
> >> To: xen-devel@lists.xenproject.org
> >> Cc: Kevin Tian <kevin.tian@intel.com>; Stefano Stabellini <sstabellini@kernel.org>; Tamas K Lengyel
> >> <tamas.lengyel@intel.com>; Jun Nakajima <jun.nakajima@intel.com>; Wei Liu <wl@xen.org>; Andrew Cooper
> >> <andrew.cooper3@citrix.com>; Ian Jackson <ian.jackson@eu.citrix.com>; George Dunlap
> >> <george.dunlap@citrix.com>; Tamas K Lengyel <tamas@tklengyel.com>; Jan Beulich <jbeulich@suse.com>;
> >> Anthony PERARD <anthony.perard@citrix.com>; Julien Grall <julien@xen.org>; Roger Pau Monné
> >> <roger.pau@citrix.com>
> >> Subject: [PATCH v19 for-4.14 00/13] VM forking
> >
> > Hi,
> >
> >  This series looks to be largely un-acked so, since we are now past the freeze date, I don't really think it can go into 4.14. Is there a particular reason that you think it should be considered?
>
> Tamas’ project itself mainly uses libxc and below, as I understand; and so getting patches 1 and 2 in would be an important milestone; both have had R-b’s before the feature freeze.  Arguably patches 1 and 2 are a bug fix.  Patch 1 is missing VMX (or a general x86).

Correct. The first two patches going in would decide whether we will
be able to use the 4.14 release without having to carry out-of-tree
patches. Although as things stand at the moment regarding all the bugs
being discovered in 4.13 and 4.14 we will likely still have to
backport all of these patches to 4.12 by hand.

> The libxl/xl side hasn’t, as I understand it, had significant review; I think that should probably wait until 4.15.

Correct. It has been sent 19 times so far over a period of 9 months
with no feedback from any of the maintainers other then that it's hard
to review. We had some good discussion with other community members
but evidently non of the toolstack maintainers care too much about it.
I made the last-ditch effort to make it easier to review but at this
point we started implementing our own toolstack to interact with VM
forks.

> What do you think, Tamas?

If it's not going into 4.14 then it's going to be dropped. It has been
made solely for the benefit of the community to make the new VM
forking more accessible and useful for others. Without it the only way
to use the feature is to implement your own toolstack. Initially we
were hoping that integrating support to xl/libxl would eliminate the
need for us to implement our own parallel toolstack but since we have
to do that now anyway there is no benefit for us in carrying these
patches any further. It's disheartening we had to resort to that and I
certainly will try to avoid contributing to xl/libxl in the future
since I personally consider it a waste of time.

Thanks,
Tamas