WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-users

Re: [Xen-users] Why limit dom0's memory?

> Oups!!!
> total_memory           : 3322
>
> while i have 8Go of RAM...
>
> i did installed a Debian i686 on a x86_64 Server. It should not be a
> problem, isn't it?

You've not got PAE support in your Xen / XenLinux; you need that for > 4GB on 
i686.  If you can find Debian Xen and XenLinux images that support PAE 
(that's CONFIG_HIGHMEM_64G in the Linux configurator, by the way) then your 
existing install should support all the memory.

> If i save all my guests, and install again my Xen Server with Debian
> x86_64 instead of i686, then i restore the guests, will there be a
> problem?

As in xm save them?  I'm not sure if the suspend images will work on x86_64 or 
not - I've never tried / checked.  But you should be able to boot 32-bit 
guests on x86_64 /as long as you have a new enough Xen/.  I don't know what 
XEn version Debian will be running.  The guests *still* need to be PAE for 
that to work, so I suggest you investigate that route on your existing system 
first.

If you set up 32-bit PAE and then want 64-bit guests later, you can use a 
64-bit Xen with a 32-bit dom0 and that will work /as long as you have a new 
enough Xen and XenLinux/.

Hope that helps some.

Cheers,
Mark

>
>
>
> root@gaia: ~ # xm info
> host                   : gaia
> release                : 2.6.18-xen
> version                : #1 SMP Fri May 18 16:11:33 BST 2007
> machine                : i686
> nr_cpus                : 4
> nr_nodes               : 1
> sockets_per_node       : 1
> cores_per_socket       : 4
> threads_per_core       : 1
> cpu_mhz                : 2660
> hw_caps                :
> bfebfbff:20100000:00000000:00000040:000ce3bd:00000000:00000001
> total_memory           : 3322
> free_memory            : 2
> xen_major              : 3
> xen_minor              : 1
> xen_extra              : .0
> xen_caps               : xen-3.0-x86_32 hvm-3.0-x86_32
> xen_scheduler          : credit
> xen_pagesize           : 4096
> platform_params        : virt_start=0xfc000000
> xen_changeset          : Fri May 18 15:52:14 2007 +0100 15042:50fe1a769660
> cc_compiler            : gcc version 3.4.4 20050314 (prerelease)
> (Debian 3.4.3-13)
> cc_compile_by          : shand
> cc_compile_domain      : localdomain
> cc_compile_date        : Fri May 18 15:53:15 BST 2007
> xend_config_format     : 4
>
>
>
>
>
>
> On Thu, Jun 19, 2008 at 3:56 PM, Mark Williamson
>
> <mark.williamson@xxxxxxxxxxxx> wrote:
> > Hi there,
> >
> >> It's strange for me.
> >> I've got 8Go of RAM.
> >> I've defined 1024M to Dom0 on the boot (/boot/grub/menu.lst)
> >> ...
> >> kernel          /xen-3.1.0.gz dom0_mem=1024M console=vga
> >> ...
> >>
> >> I've got some Guests with some Go of RAM et it still remain a lot of
> >> RAM to use that i attibue to the news guests.
> >> But the problem that when i tried to create it, i had this error:
> >>
> >> # xm create toto.cfg
> >> Using config file "/etc/xen/toto.cfg".
> >> Error: I need 1073152 KiB, but dom0_min_mem is 200704 and shrinking to
> >> 200704 KiB would leave only 675672 KiB free.
> >>
> >> # cat /etc/xen/toto.cfg
> >> ---
> >> memory  = '1048'
> >> ---
> >>
> >> If i shutdown one of my other guest, it will ok.
> >> It's strange since i defined 1Go to Dom0, i get only 853Mo
> >> # free -mo
> >>
> >>              total       used       free     shared    buffers    
> >> cached Mem:           853        190        662          0         23   
> >>      32
> >>
> >>
> >> Would someone explain me about this?
> >> i'm with Debian Etch, Xen 3.1, 8Go RAM.
> >
> > Is that "free" output from when dom0 is freshly booted, or after you've
> > started some domains?
> >
> > Although you're setting dom0_mem=1024M, which means dom0 *initially* has
> > 1GB of RAM, it looks like your dom0-min-mem setting in
> > /etc/xen/xend-config.sxp is set to 200704, which will permit dom0 to
> > shrink in order to accommodate starting other domains.  If dom0 has
> > already shrunk then the value given by "free" will be correspondingly
> > reduced.
> >
> > The error messages you're seeing are due to dom0 not being able to shrink
> > enough to accommodate your new domain, suggesting that you're running
> > short on RAM.
> >
> > xm info can be used to find out the total amount of memory that's free
> > for Xen to allocate without dom0 needing to shrink.
> >
> > Cheers,
> > Mark
> >
> >> Thank you in advance.
> >>
> >> On Thu, Jun 19, 2008 at 4:24 AM, Mark Williamson
> >>
> >> <mark.williamson@xxxxxxxxxxxx> wrote:
> >> > That said, I think many people find that for a minimal dom0, not doing
> >> > much other work about 256MB is a reasonable amount of memory.  Maybe
> >> > you'd want to go to 512MB if you had many guests and / or memory to
> >> > spare.  dom0's requirements aren't extravagent, as long as you're not
> >> > running loads of things in it (which on a server you shouldn't, for
> >> > security reasons).
> >> >
> >> > Of course if you start running X and a modern desktop, you can expect
> >> > dom0 to have significantly higher memory requirements, just as a
> >> > normal machine would ;-)
> >> >
> >> > Cheers,
> >> > Mark
> >> >
> >> > On Monday 16 June 2008, Sandor W. Sklar wrote:
> >> >> On Jun 15, 2008, at 7:37 PM, Tim Post wrote:
> >> >> > On Sun, 2008-06-15 at 17:45 -0700, Sandor W. Sklar wrote:
> >> >> >> Well, of course, the amount of memory that a dom0 needs depends
> >> >> >> upon the service running within it.  I guess I didn't word my
> >> >> >> question explicitly enough.  Is there a formula for determine how
> >> >> >> much memory a
> >> >> >> dom0 might need, given a system with X amount of RAM, and X number
> >> >> >> of guests, assuming there are no other services running in the
> >> >> >> dom0?
> >> >> >
> >> >> > You are hoping to calculate the best possible density? I.e. give
> >> >> > dom-0 xx MB per pv guest, xx MB per HVM guest?
> >> >>
> >> >> Indeed, exactly!  Not exact numbers, but a guideline that would let
> >> >> me maximize the memory available to guests without running the risk
> >> >> of starving the dom0.
> >> >>
> >> >> > Even that is too broad to really pin down, it would really depend
> >> >> > on what you give the guests and how much they exercise the disks.
> >> >>
> >> >> OK, thanks, I guess I assumed as much, given that if such information
> >> >> existed, Google would have told me.  :-)
> >> >>
> >> >>       -s-
> >> >>
> >> >>
> >> >> _______________________________________________
> >> >> Xen-users mailing list
> >> >> Xen-users@xxxxxxxxxxxxxxxxxxx
> >> >> http://lists.xensource.com/xen-users
> >> >
> >> > --
> >> > Push Me Pull You - Distributed SCM tool
> >> > (http://www.cl.cam.ac.uk/~maw48/pmpu/)
> >> >
> >> > _______________________________________________
> >> > Xen-users mailing list
> >> > Xen-users@xxxxxxxxxxxxxxxxxxx
> >> > http://lists.xensource.com/xen-users
> >>
> >> _______________________________________________
> >> Xen-users mailing list
> >> Xen-users@xxxxxxxxxxxxxxxxxxx
> >> http://lists.xensource.com/xen-users
> >
> > --
> > Push Me Pull You - Distributed SCM tool
> > (http://www.cl.cam.ac.uk/~maw48/pmpu/)



-- 
Push Me Pull You - Distributed SCM tool (http://www.cl.cam.ac.uk/~maw48/pmpu/)

_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users