Re: xilinx-zynq-a9: cannot set up guest memory 'zynq.ext_ram'

[Bin Meng]

Hi Philippe,

On Fri, Aug 20, 2021 at 10:10 PM Philippe Mathieu-Daudé
<philmd@redhat.com> wrote:
>
> Hi Bin,
>
> On 8/20/21 4:04 PM, Bin Meng wrote:
> > Hi,
> >
> > The following command used to work on QEMU 4.2.0, but is now broken
> > with QEMU head.
> >
> > $ qemu-system-arm -M xilinx-zynq-a9 -display none -m 40000000
> > -nographic -serial /dev/null -serial mon:stdio -monitor null -device
> > loader,file=u-boot-dtb.bin,addr=0x4000000,cpu-num=0
> > qemu-system-arm: cannot set up guest memory 'zynq.ext_ram': Cannot
> > allocate memory
> >
> > Any ideas?
>
> Richard hit that recently too.

I hit this when in the VM on Azure pipelines, but I was able to
reproduce this issue on my local machine.

>
> Can you provide:
>
> cat /proc/sys/vm/overcommit_kbytes
> cat /proc/sys/vm/overcommit_memory
> cat /proc/sys/vm/overcommit_ratio

$ cat /proc/sys/vm/overcommit_kbytes
0
$ cat /proc/sys/vm/overcommit_memory
0
$ cat /proc/sys/vm/overcommit_ratio
50

>
> and
>
> cat /proc/meminfo
>
> (CommitLimit, Committed_AS)

$ cat /proc/meminfo

CommitLimit:    12388820 kB
Committed_AS:    5019088 kB

> and OOM messages.

I did not see any OOM messages.

>
> Per David, 'you can trick QEMU in trying to work around
> that issue, specifying a memory-backend-ram with "reserve=off"
> as guest RAM.'

Regards,
Bin