On 09/06/2018 11:33 AM, Marek Marczykowski-Górecki wrote: > Scrubbing pages on initial balloon down can take some time, especially > in nested virtualization case (nested EPT is slow). When HVM/PVH guest is > started with memory= significantly lower than maxmem=, all the extra > pages will be scrubbed before returning to Xen. But since most of them > weren't used at all at that point, Xen needs to populate them first > (from populate-on-demand pool). In nested virt case (Xen inside KVM) > this slows down the guest boot by 15-30s with just 1.5GB needed to be > returned to Xen. > > Add runtime parameter to enable/disable it, to allow initially disabling > scrubbing, then enable it back during boot (for example in initramfs). > Such usage relies on assumption that a) most pages ballooned out during > initial boot weren't used at all, and b) even if they were, very few > secrets are in the guest at that time (before any serious userspace > kicks in). > > Default behaviour is unchanged. > > Signed-off-by: Marek Marczykowski-Górecki <marma...@invisiblethingslab.com> > > --- > Is module_param() a good thing for this? Other xen-balloon parameters are > in /sys/devices/system/xen_memory, so maybe it would make sense to put > this one there too? But then, cmdline parameter would need to be added > separately and comment about core_param() suggests it shouldn't be used > if not absolutely necessary (is it?).
You can also use cmdline_find_option() in the balloon driver. I would prefer that all tunables for the balloon driver live in the same place. (Note that in that case Documentation/ABI/stable/sysfs-devices-system-xen_memory will need to be updated). -boris _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
