>_______________________________________________
CentOS mailing list
CentOS@centos.org
http://lists.centos.org/mailman/listinfo/centos
08-30-2011, 01:30 PM
Dennis Jacobfeuerborn
new memory not getting regonized
On 08/27/2011 09:12 PM, sylvan.dcunha@gmail.com wrote:
> Dear Dennis,
>
> Thanks a lot for the wise reply.. really did boost my knowledge..
> honestly was unware of the fact that dom0 is just like another VM ...
> Anyway I had never restricted dom0 mem and since my 4 vms were working fine
> with no issues
> i never bothered much.
Yes, this is different from KVM where the VMs really are just normal
processes on the host system and the host system itself isn't a VM.
On a Xen system if you look at /etc/grub.conf you'll notice that it looks
slightly different than on a non-virtualized system. Specifically you'll
find the following line:
kernel /xen.gz-2.6.18-164.el5
That's the actual hypervisor and really the host system and once started it
will basically start dom0 and give it special privileges. So Dom0 and the
DomU's all run on top of the actual hypervisor.
> It was only after I added more 32 gb to existing 32 gb i did realise the
> above issue..
Apparently dom0 has a 32G limit but that shouldn't be an issue unless you
actually really require more than 32G specifically for dom0 and not the VMs.
> anyway I will try to restrict my dom0 to 1 GB ... and check it out.
Remember that the problems with the dynamic memory management are most
likely fixed nowadays so the limitation is not strictly necessary. But then
1G will probably be more than enough for dom0 so it doesn't really hurt either.
> but just still a litle confused why xm top & xm info shows 65gb
> and top , free and cat /proc/meminfo shows 32 gb
The xm tools show you the actual physical memory in the system while the
/proc/meminfo shows you only the memory visible to dom0 which as I
mentioned above is apparently limited to 32G.
Regards,
Dennis
_______________________________________________
CentOS mailing list
CentOS@centos.org
http://lists.centos.org/mailman/listinfo/centos
08-31-2011, 03:38 PM
Pasi Kärkkäinen
new memory not getting regonized
On Tue, Aug 30, 2011 at 03:30:46PM +0200, Dennis Jacobfeuerborn wrote:
> On 08/27/2011 09:12 PM, sylvan.dcunha@gmail.com wrote:
> > Dear Dennis,
> >
> > Thanks a lot for the wise reply.. really did boost my knowledge..
> > honestly was unware of the fact that dom0 is just like another VM ...
> > Anyway I had never restricted dom0 mem and since my 4 vms were working fine
> > with no issues
> > i never bothered much.
>
> Yes, this is different from KVM where the VMs really are just normal
> processes on the host system and the host system itself isn't a VM.
>
> On a Xen system if you look at /etc/grub.conf you'll notice that it looks
> slightly different than on a non-virtualized system. Specifically you'll
> find the following line:
> kernel /xen.gz-2.6.18-164.el5
>
> That's the actual hypervisor and really the host system and once started it
> will basically start dom0 and give it special privileges. So Dom0 and the
> DomU's all run on top of the actual hypervisor.
>
> > It was only after I added more 32 gb to existing 32 gb i did realise the
> > above issue..
>
> Apparently dom0 has a 32G limit but that shouldn't be an issue unless you
> actually really require more than 32G specifically for dom0 and not the VMs.
>
> > anyway I will try to restrict my dom0 to 1 GB ... and check it out.
>
> Remember that the problems with the dynamic memory management are most
> likely fixed nowadays so the limitation is not strictly necessary. But then
> 1G will probably be more than enough for dom0 so it doesn't really hurt either.
>
Still today you should dedicate a fixed amount of memory for dom0!
say, 1GB, or so.
It's because of how Linux kernel allocates (and wastes) page struct memory:
http://wiki.xen.org/xenwiki/XenBestPractices
-- Pasi
_______________________________________________
CentOS mailing list
CentOS@centos.org
http://lists.centos.org/mailman/listinfo/centos
08-31-2011, 07:00 PM
Dennis Jacobfeuerborn
new memory not getting regonized
On 08/31/2011 05:38 PM, Pasi Kärkkäinen wrote:
> On Tue, Aug 30, 2011 at 03:30:46PM +0200, Dennis Jacobfeuerborn wrote:
>> On 08/27/2011 09:12 PM, sylvan.dcunha@gmail.com wrote:
>>> Dear Dennis,
>>>
>>> Thanks a lot for the wise reply.. really did boost my knowledge..
>>> honestly was unware of the fact that dom0 is just like another VM ...
>>> Anyway I had never restricted dom0 mem and since my 4 vms were working fine
>>> with no issues
>>> i never bothered much.
>>
>> Yes, this is different from KVM where the VMs really are just normal
>> processes on the host system and the host system itself isn't a VM.
>>
>> On a Xen system if you look at /etc/grub.conf you'll notice that it looks
>> slightly different than on a non-virtualized system. Specifically you'll
>> find the following line:
>> kernel /xen.gz-2.6.18-164.el5
>>
>> That's the actual hypervisor and really the host system and once started it
>> will basically start dom0 and give it special privileges. So Dom0 and the
>> DomU's all run on top of the actual hypervisor.
>>
>>> It was only after I added more 32 gb to existing 32 gb i did realise the
>>> above issue..
>>
>> Apparently dom0 has a 32G limit but that shouldn't be an issue unless you
>> actually really require more than 32G specifically for dom0 and not the VMs.
>>
>>> anyway I will try to restrict my dom0 to 1 GB ... and check it out.
>>
>> Remember that the problems with the dynamic memory management are most
>> likely fixed nowadays so the limitation is not strictly necessary. But then
>> 1G will probably be more than enough for dom0 so it doesn't really hurt either.
>>
>
> Still today you should dedicate a fixed amount of memory for dom0!
> say, 1GB, or so.
>
> It's because of how Linux kernel allocates (and wastes) page struct memory:
> http://wiki.xen.org/xenwiki/XenBestPractices
Very good to know. Thanks for the information!
Regards,
Dennis
_______________________________________________
CentOS mailing list
CentOS@centos.org
http://lists.centos.org/mailman/listinfo/centos
09-08-2011, 07:12 AM
benedict dcunha
new memory not getting regonized
Dear Guys,
*
First of all thanks for all your wise replies.. a little late since was tied with some other stuff and wanted to test the change I made on my xen server
actually as dennis says ... and hes perfectly right
*
actually what I did was restrict my DOM0 mem size to 1 gb with dom0_mem=1024M in grub.conf and now top and free was showing 1 gb as my memory. also i have disabled balloning in the xend-config file as recommended
and xm top and xm info were showing me 64 gb as total memory and the free memory and the memory used by my V.Ms was equall to 64 gb which is perfect
*
So I am now clear that free and top actually shows the memory assigned to DOM 0 and not the totalsystem *memory under xen
*
Once again thaks and apprecite your responses guys..
*
*
regards
*
*
sylvan
*
*
*
On Sat, Aug 27, 2011 at 3:44 PM, Dennis Jacobfeuerborn <dennisml@conversis.de> wrote:
On 08/27/2011 02:35 PM, Simon Matter wrote:
>> Thanks Guys
>>
>> really apprecite your quick responses.
>> ( Dennis was right in tellin me about PAE since my system is 64 bit and if
>> I
>> do run yum install kernel-PAE there is nothing found.)
>>
>> actually i found something more as i was figuring my issue out.
>>
>> when I do a *top i see the following
>> Committed_AS: * 394740 kB
>> VmallocTotal: 34359738367 kB
>> VmallocUsed: * * *3304 kB
>> VmallocChunk: 34359733919 kB
>> ------------
>>
>> actually I had run the above 2 command and found the memory was 32gb
>> but as dennis said when I run the command
>> xm info
>> ----------------------
>> [root@hypervisor2 ~]# xm info
>> host * * * * * * * * * : hypervisor2
>> release * * * * * * * *: 2.6.18-194.32.1.el5xen
>> cc_compile_date * * * *: Wed Jan *5 17:43:03 EST 2011
>> xend_config_format * * : 2
>> --------------------
>> and then I ran xm top i see
>>
>> -------------
>>
>>
>> so the above 2 command show me 64gb
>>
>> Now I m confused ..
>>
>> Is my Centos XEN server actually using the 64 bit ...
>> and which command actually show me the right memory status
>
> I'm not sure but I think everything is okay with your box. "xm top" shows
> that your box run with 64Gb memory, and what "top" shows is that your Dom0
> OS runs with 32Gb memory, which means your DomU's take the other 32Gb. Did
> you up the memory settings in your virtual hosts configuration? After
> doing so you should see the Dom0 memory to go down when looking at it with
> "top".
Benedict is right. Remember that under Xen Dom0 is really just another VM
with special privileges. In fact on all my host systems I restrict Dom0 to
1G of ram by adding a "dom0_mem=1024M" argument to the grub configuration.
In practice Xen should reduce the amount of ram used by Dom0 dynamically as
needed for VMs i.e. if your virtual machines use 48G of ram then dom0
should only show 16G left. A while ago this mechanism lead to instability
though so a general recommendation was to set dom0 memory to a fixed 1G or
512M to not rely on this dynamic memory handling.
Check this out for example:
http://lists.xensource.com/archives/html/xen-users/2008-06/msg00729.html
Regards,
* Dennis
_______________________________________________
CentOS mailing list
CentOS@centos.org
http://lists.centos.org/mailman/listinfo/centos
_______________________________________________
CentOS mailing list
CentOS@centos.org
http://lists.centos.org/mailman/listinfo/centos
new memory not getting regonized
