[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] RE: Ballooning up
> From: Jeremy Fitzhardinge [mailto:jeremy@xxxxxxxx] > Cc: Dan Magenheimer; Daniel Kiper; Stefano Stabellini; Konrad Rzeszutek > Wilk > Subject: Ballooning up > > I finally got around to implementing "ballooning up" in the pvops > kernels. Now if you start a domain with "memory=X maxmem=Y", the > domain > will start with X MB of memory, but you can use "x[ml] mem-set" to > expand the domain up to Y. Nice! > As a side-effect, it also works for dom0. If you set dom0_mem on the > Xen command line, then nr_pages is limited to that value, but the > kernel > can still see the system's real E820 map, and therefore adds all the > system's memory to its own balloon driver, potentially allowing dom0 to > expand up to take all physical memory. > > However, this may caused bad side-effects if your system memory is much > larger than your dom0_mem, especially if you use a 32-bit dom0. I may > need to add a kernel command line option to limit the max initial > balloon size to mitigate this... I would call this dom0 functionality a bug. I think both Citrix and Oracle use dom0_mem as a normal boot option for every installation and, while I think both employ heuristics to choose a larger dom0_mem for larger physical memory, I don't think it grows large enough for, say, >256GB physical memory, to accommodate the necessarily large number of page tables. So, I'd vote for NOT allowing dom0 to balloon up to physical memory if dom0_mem is specified, and possibly a kernel command line option that allows it to grow beyond. Or, possibly, no option and never allow dom0 memory to grow beyond dom0_mem unless (possibly) it grows with hot-plug. Dan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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