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Re: [Xen-devel] [PATCH v3] xen/balloon: add runtime control for scrubbing ballooned out pages


  • To: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • From: Juergen Gross <jgross@xxxxxxxx>
  • Date: Mon, 10 Sep 2018 13:31:30 +0200
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  • Cc: David Rientjes <rientjes@xxxxxxxxxx>, Jonathan Corbet <corbet@xxxxxxx>, Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>, Frederic Weisbecker <frederic@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, "open list:DOCUMENTATION" <linux-doc@xxxxxxxxxxxxxxx>, open list <linux-kernel@xxxxxxxxxxxxxxx>, Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Jiri Kosina <jkosina@xxxxxxx>, Bjorn Helgaas <bhelgaas@xxxxxxxxxx>, Thymo van Beers <thymovanbeers@xxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>
  • Delivery-date: Mon, 10 Sep 2018 11:31:37 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 07/09/18 18:49, 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>

Reviewed-by: Juergen Gross <jgross@xxxxxxxx>


Juergen

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