[Pkg-xen-devel] Bug#721946: Bug#721946: xen-hypervisor-4.1-amd64: dom0_mem cannot exceed some value

[Ian Campbell]

On Thu, 2013-09-05 at 20:52 +0200, Alessandro Vesely wrote:
> Package: xen-hypervisor-4.1-amd64
> Version: 4.1.4-3+deb7u1
> Severity: normal
> 
> I tried GRUB_CMDLINE_XEN="dom0_mem=8192M":  that delivers 6964868K total, then
> crashes when used=2837436K free=4127432K.
> By crash I mean the gnome screen was blown away, replaced by a black screen
> with white log lines.  That seems to happen every time dom0 uses a large amount
> of memory.

On a modern dom0 kernel you need to specify the maximum memory as well,
i.e. dom0_mem=8192M,max:8192M otherwise the kernel will attempt to
allocate enough page tables to cover all of *host* RAM which can exhaust
its actual memory allocation. You can of course also boot "preballooned"
e.g. dom0_mem=1G,max:4G but need to be mindful of the ratio between the
two.

http://blog.xen.org/index.php/2012/04/30/memory-where-it-has-not-gone/
has some background discussion.

Ian.