Re: [Xen-devel] libxl: error: libxl.c:2150:libxl_set_memory_target new target 0 for dom0 is below the minimum threshold

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 23 Nov 2011, Ian Campbell wrote:
> On Wed, 2011-11-23 at 10:56 +0000, Stefano Stabellini wrote:
> > On Tue, 22 Nov 2011, Teck Choon Giam wrote:
> > > >> >> That means default value changed if it is unset for autoballoon?
> > > >> >> Original one is commented with #autoballoon = 1 in /etc/xen/xl.conf 
> > > >> >> so
> > > >> >> it is unset I guess so the default value for autoballoon for c/s 
> > > >> >> 23110
> > > >> >> is autoballoon=0 where c/s 23190 is autoballoon=1? Ã?Æ??Ã?â??Ã? 
> > > >> >> Just some
> > > >> >> guessing... ...
> > > >
> > > > Autoballoon and dom0_mem are incompatible.
> > > > I don't think there are any relevant differences between 23110 and 23190
> > > > on xen-unstable, maybe you used to start dom0 without dom0_mem before?
> > > 
> > > Nope... all my servers will always have those dom0_mem set.  It is
> > > from xen-4.1-testing not xen-unstable for the two changeset.
> > 
> > I still cannot see anything in that range. However as I said before, it
> > is expected that with dom0_mem set autoballoon needs to be disabled.
> 
> We still haven't seen the full node IDs of the changesets which I asked
> for so it is not obvious that we are actually looking at the same range
> of changesets...
> 
> > Maybe it is worth documenting this somewhere, any suggestions where?
> 
> xl man page? Perhaps we also need a separate /etc/xl.cfg (or whatever
> the path is) page?
> 
> If there is anywhere on the wiki which recommends dom0_mem= (and there
> should be) it should simultaneously mention this setting. As should any
> "getting started" page.
> 
> On the other hand I'm not sure why autoballoon and dom0_mem play so
> badly together. Surely if dom0_mem is used autoballon should just see
> that there is plenty of free RAM in the system and not do anything?
 
Because one of the "memory slack" paramters needed by autoballoon is

totalmemory - dom0_memory_at_boot

fortunately libxl is smart enough to trim it to 15% of the total memory
of the system, just in case a user forgot to disable autoballon but set
dom0_mem.
Ah! Now that you make me think about it, I bet the failure comes from a
system that is missing:

libxl: Introduce a maximum limit for free_mem_slack (re (dom0) ballooning)
    
    This fixes this message:
     libxl: error: libxl.c:2921:libxl_set_memory_target new target
                   for dom0 is below the minimum threshold
    which can occur spuriously if dom0_mem is specified and xl
    autoballoning is left turned on.

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