Re: [Xen-devel] can not use all available memory

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Fri, Nov 23, 2012 at 12:33:59PM +0000, Ian Campbell wrote:
> On Fri, 2012-11-23 at 12:28 +0000, Pasi Kärkkäinen wrote:
> > On Fri, Nov 23, 2012 at 12:21:32PM +0000, Ian Campbell wrote:
> > > This question belongs on xen-users.
> > > 
> > > On Fri, 2012-11-23 at 11:35 +0000, Alexander Bienzeisler wrote:
> > > > Hello,
> > > > 
> > > > i just tried to add a domU with 16 gigs of ram (maxmem = 16384, memory 
> > > > = 
> > > > 16384) with free_memory : 28969 but got an error:
> > > > 
> > > > libxl: error: libxl.c:3433:libxl_set_memory_target: new target 0 for 
> > > > dom0 is below the minimum threshold
> > > 
> > > The clue is in this message -- you cannot safely balloon down a guest
> > > (including dom0) to an arbitrarily small value relative to its initial
> > > size. The kernel will have certain fixed datastructures etc which are
> > > sized according to the maximum amount of RAM at start of day.
> > > 
> > > If you were to balloon down too low then you would run out of RAM and
> > > the OOM killer would step in and start killing stuff, so xl includes a
> > > safety catch which prevents this.
> > > 
> > > If you have a huge host and want a small dom0 use the dom0_mem option
> > > and disable xl's autoballoon option or whatever the equivalent xend
> > > option is.
> > > 
> > 
> > I think he was already using dom0_mem. He had 28969 free in Xen as
> > reported by "xl info".
> 
> Then he's missed disabling autoballoon.
> 

As can be seen from the other email in this thread,
he's using dom0_mem=2048M, and he has 28GB of free memory in Xen.

Why is xl trying to balloon down dom0 (and failing) for no reason? 

-- Pasi


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