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Re: [Xen-users] memory=x & maxmem=y

The parameter is maxmem, not max-mem.  That could be part of it.  You can get a complete list of options from "xm create --help_config".  When I found this out it was a huge help for me.

Also, it is important that you NOT specify mem=XXX on the kernel commandline (via the extra option).  That would completely break this behavior.  In other works, DO NOT specify anything like 'extra="mem=512"'.

One other thing I've done that may affect this is that I have limited my Dom0 memory at boot time.  Perhaps if it has to borrow the memory from the Dom0 it stops short.  I do this by passing the hypervisor the parameter dom0_mem=524288.

Here's the relevant section of my grub.conf:

root (hd0,0)
kernel /boot/xen.gz dom0_mem=524288 com1=38400,8n1 nmi=dom0
module /boot/vmlinuz-2.6.16.38-xen0 root=/dev/uba1 netloop.nloopbacks=2 xencons=ttyS libusual.bias="ub"

And here's a lightly modified copy of the .xen file that I just tested:

#  -*- mode: python; -*-
kernel = '/boot/vmlinuz-2.6.16.38-xenU'
memory = 2000
maxmem = 4096
name = 'XXX'
vif = [ 'bridge=xenbr0' ]
disk = [
        'phy:/dev/XXX0,sda1,w',
        'phy:/dev/XXX1,sda2,w',
        'phy:/dev/XXX2,sdb1,w!',
       ]
root = '/dev/sda1 ro'
vcpus = 2

Here's the output of a session.  The dates are to help match up with the following screenshots:

hostname ~ # date ; xm info | grep free
Mon May 21 20:10:21 PDT 2007
free_memory            : 307
hostname ~ # xm mem-set XXX 2250 ; date
Mon May 21 20:12:13 PDT 2007
hostname ~ # xm mem-set XXX 2000 ; date
Mon May 21 20:12:43 PDT 2007
hostname ~ #

Here are screenshots of before adjusting the memory, after upping it, and after dropping it again:


Here is uname -a from the DomU:

Linux XXX 2.6.16.38-xenU #1 SMP Mon Mar 26 03:15:23 PDT 2007 x86_64 Dual Core AMD Opteron(tm) Processor 280 GNU/Linux

And xm info on the Dom0:

host                   : XXW
release                : 2.6.16.38-xen0
version                : #4 SMP Mon Mar 26 22:56:07 PDT 2007
machine                : x86_64
nr_cpus                : 4
nr_nodes               : 1
sockets_per_node       : 2
cores_per_socket       : 2
threads_per_core       : 1
cpu_mhz                : 2394
hw_caps                : 178bfbff:e3d3fbff:00000000:00000010:00000001:00000000:00000003
total_memory           : 16319
free_memory            : 307
xen_major              : 3
xen_minor              : 0
xen_extra              : .4-1
xen_caps               : xen-3.0-x86_64
xen_pagesize           : 4096
platform_params        : virt_start=0xffff800000000000
xen_changeset          : Thu Feb 15 11:34:58 2007 +0000 13139:3341afbb1953
cc_compiler            : gcc version 4.1.1 (Gentoo 4.1.1-r1)
cc_compile_by          : root
cc_compile_domain      : XXW.com
cc_compile_date        : Mon Mar 26 02:54:15 PDT 2007
xend_config_format     : 3

Hopefully some of this will help somebody...but it really does work.  I swear!

On May 21, 2007, at 6:10 PM, suyash jape wrote:

    Hi everyone , I have also been facing the same problem for the past few days. The max-mem parameter in the domU  config file is completely ignored.Even if we specifiy maxmem parameter in the config file at boot time , boot time allocated memory is taken as the max memory possible for the domain.
           Also i observed that the max vcpu parameter also behaves the same way.
VCPU Observations:
1]We can play around with only the no of VCPUs allotted at boot time or less.

Allocating max no of VCPUs  dynamically is not reflected. i.e we can make max VCPUs of a domain from 5 to 10 dynamically BUT the 5 new ones are never used...they are always paused (possibly a bug in open source xen ?)

Is there a fix around these problems?

Thanks.....

Suyash


 
Paul Archer <tigger@xxxxxx> wrote:

> I have been playing with memory= and maxmem=, but I'm not seeing what
> I think I should be seeing, namely that the memory available to a
> domU can be increased on the fly.
>
>

Brad wrote :
>I wasn't able to achieve this using xen-3.1. The maximum amount of RAM appears to be dictated by the value that >the machine is booted with. Has anyone else managed to increase the amount of memory allocated to a domU to >more than what the domU was booted with and have the domU utilise this memory? I.e. show up with free -m on the >domU?
      
 
 

  
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Jayson Vantuyl
Systems Architect


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