Re: [Xen-users] very strange problem: memory memory?

["chengkunck@xxxxxxxxx" <chengkunck@xxxxxxxxx>]

Hi Lee,

    I think that it maybe not the VM who remembers the memory configuration. First, I've never met this problem mostly because my domus run linux and I seldomly change their configs. Then, it did remind me something that for a physical machine the BIOS would monitor the hardware changes, especially when you have a Windows and plug or unplug a memory chip. 

    So my guess is it might be with the hypervisor, if my memory is correct, I remember there's also a mechanism for VM that serves as the BIOS. 'ROMBIOS', it seems to be that name.

---

Best regards,

       Kenneth

 

From: Ian Campbell

Date: 2014-11-17 17:54

To: lee

CC: xen-users

Subject: Re: [Xen-users] very strange problem: memory memory?

On Sat, 2014-11-15 at 00:26 +0100, lee wrote:

> Hi,

>

> does xen, or do domUs, somehow remember how much memory they had

> assigned to them?

>

> I've upgraded the memory of the server from 8GB to 36GB (8x4 + 4*1 GB),

> following the instructions in the manual about how to populate the

> banks.  So far, the server is running fine.

>

> I have a VM which used to have 'memory = 3107' in its configuration.

> When I change the number to 10240 or 8192 or 4096 or even 3110, the VM

> crashes early during the boot process.  Change it back to 3107 and the

> VM runs fine.

>

> There are other domUs that crash when they are booting when I change the

> amount of memory assigned to them, like from 384MB to 512MB.  Change it

> back to 384MB and the VM runs fine.  Only for two or three VMs, I was

> able to increase the memory.

>

> Dom0 and all domUs are running Debian Wheezy.

>

>

> Any idea what's going on here?  Am I doing something wrong?

>

> The only thing that comes to mind is that for some reason, there's a

> strange problem with RAM modules of different sizes.  But if that's the

> case, why is the server (IBM x3650 l2g) running fine?

 

Have you run memtest or something similar? It may be that some memory is

not used until you start a VM, because it is just in the free pool.

 

Ian.

 

 

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