Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1386026

Re: [PATCH kernel 0/2] speed up live migration by skipping free pages

Show all headers | View raw

On (Tue) 19 Apr 2016 [22:34:32], Liang Li wrote:
> Current QEMU live migration implementation mark all guest's RAM pages
> as dirtied in the ram bulk stage, all these pages will be processed
> and it consumes quite a lot of CPU cycles and network bandwidth.
> 
> From guest's point of view, it doesn't care about the content in free
> page. We can make use of this fact and skip processing the free
> pages, this can save a lot CPU cycles and reduce the network traffic
> significantly while speed up the live migration process obviously.
> 
> This patch set is the kernel side implementation.
> 
> The virtio-balloon driver is extended to send the free page bitmap
> from guest to QEMU.
> 
> After getting the free page bitmap, QEMU can use it to filter out
> guest's free pages. This make the live migration process much more
> efficient.
> 
> In order to skip more free pages, we add an interface to let the user
> decide whether dropping the cache in guest during live migration.

So if virtio-balloon is the way to go (i.e. speed is acceptable), I
just have one point then.  My main concern with using (or not using)
virtio-balloon was that a guest admin is going to disable the
virtio-balloon driver entirely because the admin won't want the guest
to give away pages to the host, esp. when the guest is to be a
high-performant one.

In this case, if a new command can be added to the balloon spec where
a guest driver indicates it's not going to participate in ballooning
activity (ie a guest will ignore any ballooning requests from the
host), but use the driver just for stats-sharing purposes, that can be
a workable solution here as well.  In that case, we can keep the
MM-related stuff inside the balloon driver, and also get the benefit
of the guest having control over how it uses its memory,
disincentivising guest admins from disabling the balloon entirely (it
will also benefit the guest to keep this driver loaded in such a
state, if migration is faster!).

		Amit

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH kernel 0/2] speed up live migration by skipping free pages Liang Li <liang.z.li@intel.com> - 2016-04-19 16:50 +0200
  [PATCH kernel 2/2] virtio-balloon: extend balloon driver to support the new feature Liang Li <liang.z.li@intel.com> - 2016-04-19 16:50 +0200
    Re: [PATCH kernel 2/2] virtio-balloon: extend balloon driver to  support the new feature "Michael S. Tsirkin" <mst@redhat.com> - 2016-04-19 18:20 +0200
  Re: [PATCH kernel 0/2] speed up live migration by skipping free pages Amit Shah <amit.shah@redhat.com> - 2016-04-25 08:10 +0200
    Re: [PATCH kernel 0/2] speed up live migration by skipping free pages "Michael S. Tsirkin" <mst@redhat.com> - 2016-04-25 13:10 +0200
      Re: [PATCH kernel 0/2] speed up live migration by skipping free pages Amit Shah <amit.shah@redhat.com> - 2016-04-25 14:10 +0200
        Re: [PATCH kernel 0/2] speed up live migration by skipping free pages "Michael S. Tsirkin" <mst@redhat.com> - 2016-04-25 15:00 +0200
          Re: [PATCH kernel 0/2] speed up live migration by skipping free pages "Dr. David Alan Gilbert" <dgilbert@redhat.com> - 2016-04-25 15:20 +0200

csiph-web