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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2012-11-23 at 12:41 +0000, Pasi KÃrkkÃinen wrote:
> On Fri, Nov 23, 2012 at 12:33:59PM +0000, Ian Campbell wrote:
> > On Fri, 2012-11-23 at 12:28 +0000, Pasi KÃrkkÃinen 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? 

Because autoballoon is enabled.

This has been discussed at length on the list before, please check the
archives.

Ian.


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