Re: [Xen-users] Memory allocation

["Badyk, Benjamin" <bbadyk@xxxxxxxxxxx>]

Also, im running with the "xen-3.0-x86_32-rhel4.1.bin" distro...

On 10/2/06 11:09 AM, "Petersson, Mats" <Mats.Petersson@xxxxxxx> wrote:

>  
> 
>> -----Original Message-----
>> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
>> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of
>> Badyk, Benjamin
>> Sent: 02 October 2006 16:56
>> To: xen-users@xxxxxxxxxxxxxxxxxxx
>> Subject: [Xen-users] Memory allocation
>> 
>> I¹m sure this has been asked a bazillion times on this list,
>> but I couldn¹t
>> find a definitive answer:
>> 
>> 4GB ram,  3 domU¹s
>> 
>> I boot each domU up with 1GB ram, then mem-max and mem-set them to 2GB
>> (which obviously exceeds physical memory limit). They all
>> grow to 2048. It
>> seems that you won¹t see the memory hit 2gb on a domU until
>> it has eaten up
>> more than what it initially booted with, which is fine. The
>> question I have
>> is what would happen if all three domU¹s tried using 2GB?
> 
> If this actually works in the latest (unstable) release of Xen, I suggest you
> report a bug. 
> 
> Something will go horribly wrong if you have 3 domU's using 6GB of RAM on a
> machine with 4GB or actual memory - it should not be possible to set it like
> that. 
> 
> Xen doesn't support "swapping" or in other ways overcommitting memory within
> the domain memory allocation, so somewhere, you'll have allocated the same
> memory to more than one domain [assuming "xm list" shows all three domains to
> have 2GB of RAM each] - which would obviously not work right... But I seem to
> remember someone sending patches for "sanity checking mem-set", so it may be
> that it's fixed in the latest version.
> 
> I can certainly guarantee that the one or more domains will crash and/or
> corrupt themselves if you succeed in setting 2GB each for 3 domU's on a 4GB
> machine... [Not to mention that dom0 needs some memory, as does Xen itself -
> even if it's only some small measures of memory...]
> 
> --
> Mats
>> 
>> Thanks,
>> 
>> BJ Badyk
>> 
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>> Xen-users@xxxxxxxxxxxxxxxxxxx
>> http://lists.xensource.com/xen-users
>> 
>> 
>> 
> 
> 


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