On 9/7/18 12:49 PM, 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). > Convert CONFIG_XEN_SCRUB_PAGES to CONFIG_XEN_SCRUB_PAGES_DEFAULT (also > enabled by default), controlling default value for the new runtime > switch. > > Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx> Applied to for-linux-4.19b. -boris
