From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
To: George Dunlap <george.dunlap@eu.citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>,
Ian Campbell <ian.campbell@citrix.com>,
Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <Ian.Jackson@eu.citrix.com>,
Don Slutz <dslutz@verizon.com>,
"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: QEMU bumping memory bug analysis
Date: Tue, 16 Jun 2015 17:44:52 +0100 [thread overview]
Message-ID: <alpine.DEB.2.02.1506161721190.21829@kaball.uk.xensource.com> (raw)
In-Reply-To: <5576CC19.4070300@eu.citrix.com>
On Tue, 9 Jun 2015, George Dunlap wrote:
> On 06/09/2015 11:14 AM, Stefano Stabellini wrote:
> > On Mon, 8 Jun 2015, George Dunlap wrote:
> >> I think that qemu needs to tell libxl how much memory it is using for
> >> all of its needs -- including option ROMs. (See my example below.) For
> >> older qemus we can just make some assumptions like we always have.
> >
> > I'll just note that I have still not seen any evidence that telling
> > libxl would improve things. It seems to me that we are just adding one
> > more layer of indirection just to solve the migration issue elsewhere.
> > I haven't seen convincing examples that things would be better by telling
> > libxl yet, except that we would be able to fix the migration problem.
>
> So from a migration perspective, I agree there's not much difference
> between "libxl reads max_pages from Xen, inserts it into the migration
> stream, and sets it again on the other side" and "libxl has global
> knowledge of what max_pages should be, inserts it into the migration
> stream, and sets it again on the other side".
>
> Improvements of having it in libxl:
>
> 1. libxl is not an external interface; we can change and improve things
> as we go along.
Actually libxl is an external interface, did you mean libxc?
> Whatever we put in qemu we have to support indefinitely.
The maxmem call is already in QEMU :-)
> 2. We can begin to solve the "where is the memory" mess that is the
> current state of things.
>
> 3. In particular, we could conceivably actually change the interface to
> be consistent, so that "memory" means "the maximum amount of memory used
> by the guest including all overhead", rather than the random who knows
> what we have now.
That's it, I agree. But the issue is that we don't have a solution or
even the design of a solution. If we had, and the plan included
reverting the QEMU commit, then fine, let's do it.
> This will be impossible if we do it in qemu.
>
> Having more than one place change max_pages would be poor design even if
> we were still packaging everything together in the same release. Having
> an external entity with which we must be backwards-compatible change
> max_pages it is just a bad idea and always was.
I disagree, if it was such an obvious design mistake, more people would
have picked up on it immediately when the patch was posted the first
time around. This is blurry terrain at best.
> > When I committed it, I didn't
> > do it without thinking. I don't think that libxl should be in the middle
> > of this, because I don't think it has anything to add.
>
> Just to be clear, nobody thinks you did (at least, as far as I know).
> The problem is that all of us are so specialized: some people work
> almost entirely within qemu, others in the kernel, others in the
> toolstack, others in Xen. It's just natural for people who work mainly
> within one component to look at the problem from a particular
> perspective. But it causes exactly this sort of problem, where the left
> hand doesn't know what the right hand is doing, and the overall system
> is really uncoordinated.
That is true.
next prev parent reply other threads:[~2015-06-16 16:44 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-05 16:43 QEMU bumping memory bug analysis Wei Liu
2015-06-05 16:58 ` Ian Campbell
2015-06-05 17:13 ` Stefano Stabellini
2015-06-05 19:06 ` Wei Liu
2015-06-05 17:17 ` Andrew Cooper
2015-06-05 17:39 ` Wei Liu
2015-06-05 17:10 ` Stefano Stabellini
2015-06-05 18:10 ` Wei Liu
2015-06-08 11:39 ` Stefano Stabellini
2015-06-08 12:14 ` Andrew Cooper
2015-06-08 13:01 ` Stefano Stabellini
2015-06-08 13:33 ` Jan Beulich
2015-06-08 13:10 ` Wei Liu
2015-06-08 13:27 ` Stefano Stabellini
2015-06-08 13:32 ` Wei Liu
2015-06-08 13:38 ` Stefano Stabellini
2015-06-08 13:44 ` Andrew Cooper
2015-06-08 13:45 ` Stefano Stabellini
2015-06-05 18:49 ` Ian Campbell
2015-06-08 11:40 ` Stefano Stabellini
2015-06-08 12:11 ` Ian Campbell
2015-06-08 13:22 ` Stefano Stabellini
2015-06-08 13:52 ` Ian Campbell
2015-06-08 14:20 ` George Dunlap
2015-06-08 15:01 ` Don Slutz
2015-06-08 15:37 ` George Dunlap
2015-06-08 16:06 ` Don Slutz
2015-06-09 10:00 ` George Dunlap
2015-06-09 10:17 ` Wei Liu
2015-06-09 10:14 ` Stefano Stabellini
2015-06-09 11:20 ` George Dunlap
2015-06-16 16:44 ` Stefano Stabellini [this message]
2015-06-09 12:45 ` Ian Campbell
2015-06-17 13:35 ` Stefano Stabellini
2015-06-08 14:53 ` Konrad Rzeszutek Wilk
2015-06-08 15:20 ` George Dunlap
2015-06-08 15:42 ` Konrad Rzeszutek Wilk
2015-06-08 14:14 ` George Dunlap
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=alpine.DEB.2.02.1506161721190.21829@kaball.uk.xensource.com \
--to=stefano.stabellini@eu.citrix.com \
--cc=Ian.Jackson@eu.citrix.com \
--cc=andrew.cooper3@citrix.com \
--cc=dslutz@verizon.com \
--cc=george.dunlap@eu.citrix.com \
--cc=ian.campbell@citrix.com \
--cc=wei.liu2@citrix.com \
--cc=xen-devel@lists.xen.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.