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Re: [Xen-users] memory quesion

To: "Fajar A. Nugraha" <fajar@xxxxxxxxx>
Subject: Re: [Xen-users] memory quesion
From: Paras pradhan <pradhanparas@xxxxxxxxx>
Date: Mon, 14 Dec 2009 14:13:47 -0600
Cc: Xen Users <xen-users@xxxxxxxxxxxxxxxxxxx>
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Thanks Fajar for the info.

I set dom0_mem to 1G and here is my several outputs .

xm li:

Name                                      ID Mem(MiB) VCPUs State   Time(s)
Domain-0                                   0     1024    16 r-----    116.6

free -m:

             total       used       free     shared    buffers     cached
Mem:          1024        582        441          0         25        296
-/+ buffers/cache:        260        763
Swap:        32765          0      32765

xm info:

total_memory           : 65530
free_memory            : 63257

I believe I am doing good now !


On Fri, Dec 11, 2009 at 8:39 PM, Fajar A. Nugraha <fajar@xxxxxxxxx> wrote:
On Sat, Dec 12, 2009 at 5:57 AM, Paras pradhan <pradhanparas@xxxxxxxxx> wrote:
>> AFAIK it's a "limitation" of RHEL's kernel-xen. They did it for a very
>> good reason though: providing a usable dom0 system on servers with >=
>> 32GB memory.
> For a dom0 to be usable and stable, i guess 32 GB of memory is not needed.

Actually, the case is, if you have 64GB memory, and all of them is
made available initially to dom0, and later it was balloon down (for
domU) to (for example) 2GB, you'll be having problems. To prevent
that, the initial dom0 memory is limited by default to be 32GB max.

> Around 1GB should be enough(?)

If dom0 does not run any additional services, yes, it should be more
than enough.

> and this 1 GB is set using dom0_mem=1Gb

kernel /xen.gz dom0_mem=512M

> So is it still true that domU can use memory more than 32GB whereas it is
> showing up only 32G? I will having around 20 virtual machines and each will
> use 1 to 2 CPU and 2 GB of RAM.

Yes. If domU in total uses about 40GB, they will use the 32GB unused
plus another 8GB taken from dom0.


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