Bug#606964: linux-image-2.6.32-5-xen-amd64: Xen fails to boot dom0 kernel on system with, lots of RAM
On Mon, 2010-12-13 at 11:42 +0100, Rik Theys wrote:
> Package: linux-2.6
> Version: 2.6.32-29
> Severity: normal
>
> When booting Xen 4.0.1 with the Debian dom0 kernel, Xen hangs on startup
> after saying that the
> system has x VCPUS and before starting the "Scrubbing Free RAM".
> This looks related to the bug mentioned here:
>
> http://lists.xensource.com/archives/html/xen-devel/2010-08/msg00625.html
>
> When adding dom0_mem=2G to the boot line, the system boots OK.
I expect it will work ok with everything up to and including
dom0_mem=32G?
> I've added it to both the kernel command line and the xen command line
> to make sure I had
> the parameter set.
>
> The system has 72GB ram.
>
> The thread mentions a kernel config that can be changed to fix this?
> http://lists.xensource.com/archives/html/xen-devel/2010-08/msg00884.html
Changing this option imposes a static (at compile time) memory overhead
on the kernel when running under Xen. It has become more dynamic in
future kernels but those changes are not suitable for backporting to
Squeeze at this stage. 32GB seems like a reasonable compromise in the
meantime.
It depends a bit on your usecase but it is often best recommended to use
dom0_mem= anyway, since you are most often going to balloon dom0 down
significantly anyway to make room for guest domains.
Note also that the smallest size you can balloon dom0 to is proportional
to the initial size of the domain, due to various data structures (such
as the frame table) which are sized on boot according to memory size.
IIRC a72GB domain 0 would have several hundred megabytes of such data
structures which would therefore not be available for guest use and
effectively be wasted. If you use dom0_mem then those datastructures are
much smaller which leaves more memory for guests.
I would recommend that you determine how big you want/need domain 0 to
be and pass an appropriate dom0_mem option.
Ian,
--
Ian Campbell
Current Noise: Devin Townsend - Addicted
I consider the day misspent that I am not either charged with a crime,
or arrested for one.
-- "Ratsy" Tourbillon
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