Xen devel - Jul 2010 - xl list vs xm list: backwards compatibility vs forward progress?

I was pleased to find out that "xl list" shows the
current amount of physical memory in use by a domain
rather than the start amount.  This is very useful
for monitoring self-ballooning!  I like it!

But... it is not backwards compatible with "xm list".
Does this matter?  Probably not, but I''ve heard there
are tools that screen-scrape output from the core
xen tools... and I wonder if the other xend interface
(xapi?) gets one rather the other (or maybe both).

Just thought it should be noted, especially if
(IIRC) there are plans to symlink /usr/bin/xm
to /usr/bin/xl.

Dan

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Dan Magenheimer writes ("[Xen-devel] xl list vs xm list: backwards
compatibility vs forward progress?"):
> I was pleased to find out that "xl list" shows the
> current amount of physical memory in use by a domain
> rather than the start amount.  This is very useful
> for monitoring self-ballooning!  I like it!
> 
> But... it is not backwards compatible with "xm list".
Isn''t it ?

I''m pretty sure I''ve written a program which does "xm
mem-set" and
then polls the output from "xm list" to wait for the target domain to
balloon down.

Ian.

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> From: Ian Jackson [mailto:Ian.Jackson@eu.citrix.com]
> Sent: Wednesday, July 28, 2010 7:56 AM
> To: Dan Magenheimer
> Cc: Xen-Devel (xen-devel@lists.xensource.com)
> Subject: Re: [Xen-devel] xl list vs xm list: backwards compatibility vs
> forward progress?
> 
> Dan Magenheimer writes ("[Xen-devel] xl list vs xm list: backwards
> compatibility vs forward progress?"):
> > I was pleased to find out that "xl list" shows the
> > current amount of physical memory in use by a domain
> > rather than the start amount.  This is very useful
> > for monitoring self-ballooning!  I like it!
> >
> > But... it is not backwards compatible with "xm list".
> 
> Isn''t it ?
> 
> I''m pretty sure I''ve written a program which does
"xm mem-set" and
> then polls the output from "xm list" to wait for the target
domain to
> balloon down.
Hmmm... perhaps xm keeps track of xm mem-set commands... but a
domain can do ballooning without involvement of the toolchain.
Self-ballooning (see xen.hg/tools/xenballoon, in tree for about
two years now) does that in-guest-userland and I have kernel rpms
for EL5u5 and RHEL6b2 that do it in-guest-kernel.  (The latter
will be the preferred guest deployment method for Xen systems
running tmem to optimize memory utilization.)

With self-ballooning in a guest, xl list and xm list
very definitely show different values for memory.

Dan

P.S. Frankly, I think the xm list behavior is a bug, but
backwards compatibility -- plus my poor parseltongue --
stopped me from trying to fix it.

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On Wed, 28 Jul 2010, Dan Magenheimer wrote:
> > From: Ian Jackson [mailto:Ian.Jackson@eu.citrix.com]
> > Sent: Wednesday, July 28, 2010 7:56 AM
> > To: Dan Magenheimer
> > Cc: Xen-Devel (xen-devel@lists.xensource.com)
> > Subject: Re: [Xen-devel] xl list vs xm list: backwards compatibility
vs
> > forward progress?
> > 
> > Dan Magenheimer writes ("[Xen-devel] xl list vs xm list:
backwards
> > compatibility vs forward progress?"):
> > > I was pleased to find out that "xl list" shows the
> > > current amount of physical memory in use by a domain
> > > rather than the start amount.  This is very useful
> > > for monitoring self-ballooning!  I like it!
> > >
> > > But... it is not backwards compatible with "xm list".
> > 
> > Isn''t it ?
> > 
> > I''m pretty sure I''ve written a program which does
"xm mem-set" and
> > then polls the output from "xm list" to wait for the target
domain to
> > balloon down.
> 
> Hmmm... perhaps xm keeps track of xm mem-set commands... but a
> domain can do ballooning without involvement of the toolchain.
> Self-ballooning (see xen.hg/tools/xenballoon, in tree for about
> two years now) does that in-guest-userland and I have kernel rpms
> for EL5u5 and RHEL6b2 that do it in-guest-kernel.  (The latter
> will be the preferred guest deployment method for Xen systems
> running tmem to optimize memory utilization.)
> 
> With self-ballooning in a guest, xl list and xm list
> very definitely show different values for memory.
> 
> Dan
> 
> P.S. Frankly, I think the xm list behavior is a bug, but
> backwards compatibility -- plus my poor parseltongue --
> stopped me from trying to fix it.
> 
I agree, xm list should be the one to be fixed.

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