Hi Guys, Is possible in xen to allocate more memory to virtual machines than the real memory? I.E: vm1- 256Mb vm2- 512Mb vm3- 256Mb BUT, in my Dom0 (real machine) I has just 512Mb. Thanks in advance, Att. Artur Baruchi _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Thanks for your answer... I asked this, cause Im wondering why the balloon driver exists in Xen... Im not able to allocate more memory than configured in guest config file and by default the target AND the current allocation has the same value, so why I would touch in this value if I cannot allocate the memory freed to another domain since its denied... Do you know a situation where the balloon driver is necessary in xen? Thanks in advance.. Att. Artur Baruchi On Tue, Sep 9, 2008 at 5:02 PM, Rudi Ahlers <rudiahlers@gmail.com> wrote:> > > On Tue, Sep 9, 2008 at 9:57 PM, Artur Baruchi <mail.baruchi@gmail.com> > wrote: >> >> Hi Guys, >> >> Is possible in xen to allocate more memory to virtual machines than >> the real memory? >> I.E: >> vm1- 256Mb >> vm2- 512Mb >> vm3- 256Mb >> BUT, in my Dom0 (real machine) I has just 512Mb. >> >> Thanks in advance, >> >> Att. >> Artur Baruchi >> > > No, it''s not. You can only allocate as much memory as the physical machine > has - minus some RAM for the dom0 to work. > > > > -- > > Kind Regards > Rudi Ahlers >_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Tue, Sep 9, 2008 at 3:23 PM, Artur Baruchi <mail.baruchi@gmail.com> wrote:> Thanks for your answer... I asked this, cause Im wondering why the > balloon driver exists in Xen... Im not able to allocate more memory > than configured in guest config file and by default the target AND the > current allocation has the same value, so why I would touch in this > value if I cannot allocate the memory freed to another domain since > its denied... > > > Do you know a situation where the balloon driver is necessary in xen?you can set maximum and minimum limits for each DomU. the balloon driver then lets you shuffle memory around. of course, at any moment, the total usage can''t exceed the real RAM. also, usually the Dom0 is ballooned itself. that way it can use more RAM when you''re not running too many DomUs -- Javier _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Hi> Is possible in xen to allocate more memory to virtual machines than thereal memory? Yes and No. You can "prepare" domUs to use some amount of memory, and then assign it some lower memory. The sum of all "prepared" memory sizes MAY exceed the total amount of real memory. The sum of the assigned memory sizes MAY NOT exceed the total amount of real memory. Also note, that the dom0 itself also counts. (It usually is prepared to use ALL memory and only uses what''s left from the domUs.) Also note, that "total or real memory" in this context always refers to the amount of memory you have physically installed MINUS the memory Xen itself needs/uses. So the sum of all running domains (including dom0) can never reach you physical memory limit. Regards, Steffen _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
I see now. This balloon has the same behavior of ESX Balloon driver (http://www.usenix.org/events/osdi02/tech/waldspurger/waldspurger_html/node6.html). One thing that I noted is.. when a new guest domain is create, the dom0 limit is changed to memory_size - vm_memory_size. When I destroy this guest, the dom0 still has the new limit, this isnt changed back to memory_size. Thanks in advance, Att. Artur Baruchi On Tue, Sep 9, 2008 at 7:52 PM, Steffen Heil <lists@steffen-heil.de> wrote:> Hi > >> Is possible in xen to allocate more memory to virtual machines than the > real memory? > > Yes and No. > > You can "prepare" domUs to use some amount of memory, and then assign it > some lower memory. > > The sum of all "prepared" memory sizes MAY exceed the total amount of real > memory. > The sum of the assigned memory sizes MAY NOT exceed the total amount of real > memory. > > Also note, that the dom0 itself also counts. (It usually is prepared to use > ALL memory and only uses what''s left from the domUs.) > > Also note, that "total or real memory" in this context always refers to the > amount of memory you have physically installed MINUS the memory Xen itself > needs/uses. > So the sum of all running domains (including dom0) can never reach you > physical memory limit. > > Regards, > Steffen > >_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Xen 3.3 supports memory overcommitment now. see: http://blog.xen.org/index.php/2008/08/27/xen-33-feature-memory-overcommit/ Cheers, Todd -- Todd Deshane http://todddeshane.net check out our book: http://runningxen.com _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
I did the same thing using xen 3.2 latter. I retrieve some memory and create new guests. The sum of all domU''s memory is greater than real memory. And, I saw something nice... when I return some memory to xen the guest see this and update the memory available to the SO, for example, If the guest has 1gb and I use commands like "free" or "top", I see 1gb. When I return 512M to xen, this commands show me an updated value of 512M of available memory. So... Does xen implement some kind of Hotplug Memory for paravirtualized guests? And thanks for the last paper... I got some ideas from there... Att. Artur Baruchi On Sat, Sep 13, 2008 at 8:43 PM, Todd Deshane <deshantm@gmail.com> wrote:> Xen 3.3 supports memory overcommitment now. > > see: > http://blog.xen.org/index.php/2008/08/27/xen-33-feature-memory-overcommit/ > > Cheers, > Todd > > > -- > Todd Deshane > http://todddeshane.net > check out our book: http://runningxen.com >_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Forget my answers... I discovered what is.. The free command uses /proc/meminfo to get memory information... this entry, uses the totalram_pages and this "variable" is updated by balloon... Its more efficient than memory hotplug, since hotplug works just large amount of memory.. Anyway.. thanks! Att. Artur Baruchi On Wed, Sep 17, 2008 at 8:46 PM, Artur Baruchi <mail.baruchi@gmail.com> wrote:> I did the same thing using xen 3.2 latter. I retrieve some memory and > create new guests. The sum of all domU''s memory is greater than real > memory. > And, I saw something nice... when I return some memory to xen the > guest see this and update the memory available to the SO, for example, > If the guest has 1gb and I use commands like "free" or "top", I see > 1gb. When I return 512M to xen, this commands show me an updated value > of 512M of available memory. > > So... Does xen implement some kind of Hotplug Memory for > paravirtualized guests? > > And thanks for the last paper... I got some ideas from there... > > Att. > Artur Baruchi > > > On Sat, Sep 13, 2008 at 8:43 PM, Todd Deshane <deshantm@gmail.com> wrote: >> Xen 3.3 supports memory overcommitment now. >> >> see: >> http://blog.xen.org/index.php/2008/08/27/xen-33-feature-memory-overcommit/ >> >> Cheers, >> Todd >> >> >> -- >> Todd Deshane >> http://todddeshane.net >> check out our book: http://runningxen.com >> >_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users