Hi all, I have searched in vain on google for tips on memory sizing but have had no luck. What are the guidelines for allocating memory amongst the Dom0 and the DomUs? As an example, I have a Xen server that has 2 GB memory. I want to create 2 DomUs. If these were standalone machines, 1GB each would be fine. How would I partition this memory under Xen? Thanks in advance! Paul _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Fri, Oct 19, 2007 at 09:46:36AM -0400, Paul Waldo wrote:> > I have searched in vain on google for tips on memory sizing but have had > no luck. What are the guidelines for allocating memory amongst the Dom0 > and the DomUs?dom0: advises range from reserving 128MB to 512MB if you arent running heavy applications in dom0 (which should be moved into domUs). domU: The kernel and applications running there handle memory as they do on usual servers, so size as usual here, mainly depending on the applications you will run.> As an example, I have a Xen server that has 2 GB memory. I want to > create 2 DomUs. If these were standalone machines, 1GB each would be > fine. How would I partition this memory under Xen?256MB for dom0, rest split up for the 2 domU would be my guess. Christian _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> 256MB for dom0, rest split up for the 2 domU would be my guess.If you''re running a light dom0 that''s not running lots of other services / apps, that''d be a good place to start testing (then raise this, if necessary). I''d have thought it ought to run OK. I generally recommend people set dom0''s memory on the Xen command line (using dom0_mem=) rather than ballooning it to the right size. Extensive ballooning has been known in the past to cause Linux to get confused; you really don''t want Linux acting up in dom0, so I generally recommend people cut the ballooning out altogether. Cheers, Mark -- Dave: Just a question. What use is a unicyle with no seat? And no pedals! Mark: To answer a question with a question: What use is a skateboard? Dave: Skateboards have wheels. Mark: My wheel has a wheel! _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Christian Horn wrote:> On Fri, Oct 19, 2007 at 09:46:36AM -0400, Paul Waldo wrote: > >> I have searched in vain on google for tips on memory sizing but have had >> no luck. What are the guidelines for allocating memory amongst the Dom0 >> and the DomUs? >> > dom0: advises range from reserving 128MB to 512MB if you arent running heavy > applications in dom0 (which should be moved into domUs). > domU: The kernel and applications running there handle memory as they do > on usual servers, so size as usual here, mainly depending on the > applications you will run. > > >> As an example, I have a Xen server that has 2 GB memory. I want to >> create 2 DomUs. If these were standalone machines, 1GB each would be >> fine. How would I partition this memory under Xen? >> > 256MB for dom0, rest split up for the 2 domU would be my guess. > > > Christian >Thanks for the reply, Christian. The only services I plan on running on dom0 are ones that support the domU, so it should be pretty light. I guess the main issue is disk caching. Linux uses free memory to cache disk, so where should that happen, the dom0 or the domU? Paul _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Sat, Oct 20, 2007 at 07:27:35AM -0400, Paul Waldo wrote:> Christian Horn wrote: > > > >256MB for dom0, rest split up for the 2 domU would be my guess. > > > > > >Christian > > > Thanks for the reply, Christian. The only services I plan on running on > dom0 are ones that support the domU, so it should be pretty light. I > guess the main issue is disk caching. Linux uses free memory to cache > disk, so where should that happen, the dom0 or the domU?I think it should be done in the dom0: imagine just one spindle of disks and some domUs running and doing i/o on it, i.e. a bonnie benchmark. The dom0 should be the place where - the caching happens; imagine the domU access all the same filesystem in a readonly-mode, they shouldnt buffer the contents but dom0, as that reduces the memory used to buffer the same content - the dom0 should know best about all i/o operations that the domU try to perform, so i.e. the elevator-algorithms in the domUs should be disabled and the dom0 is the place to calculate that. I havent optimized installations for this yet, would like to hear other opinions on that... Christian _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users