Messages in this thread | | | Date | Thu, 6 Sep 2018 22:31:28 +0200 | From | Marek Marczykowski-Górecki <> | Subject | Re: [PATCH] xen/balloon: add runtime control for scrubbing ballooned out pages |
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On Thu, Sep 06, 2018 at 04:14:50PM -0400, Boris Ostrovsky wrote: > 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 <marmarek@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).
Ok, will move that. This will also mean that it will affect only balloon driver, not other users of mem-reservation.c (grant allocator). But given the reason for this tunable, I think that's fine.
-- Best Regards, Marek Marczykowski-Górecki Invisible Things Lab A: Because it messes up the order in which people normally read text. Q: Why is top-posting such a bad thing? [unhandled content-type:application/pgp-signature] | |