Re: [Qemu-devel] [PATCH v2 0/3] migration capability to discard the migrated ram pages

[Pavel Butsykin]

On 07.03.2017 16:56, Dr. David Alan Gilbert wrote:
> * Pavel Butsykin (address@hidden) wrote:
> > On 14.02.2017 17:02, Dr. David Alan Gilbert wrote:
> > > Hi Pavel,
> > >     I was curious, having merged this, how you're using postcopy; do you switch
> > > into postcopy mode immediately or wait until the first sync or what?
> > > Do you find yourself in postcopy mode long enough that it's worth
> > > doing the release?  If so on what size VMs are you working with?
> > >
> > > Dave
> >
> > Hi Dave,
> > I'm sorry it took so long, I was on vacation. And thanks for the quick
> > review and merge!
> >
> > We want to use this function to update Qemu without rebooting VMs. It
> > looks like a local migration on the same host. Now, switching into
> > postcopy mode is done immediately, the size of VMs can be very
> > different.
>
> Thanks! Do you have libvirt magic to do that update?

Yes, there are patches that add a flag "--local" for migration. The
flag adds start incoming VM and other magic about replacement source on
destination.

> Dave
>
> > > * Pavel Butsykin (address@hidden) wrote:
> > > > This feature frees the migrated memory on the source during postcopy-ram
> > > > migration. In the second step of postcopy-ram migration when the source vm
> > > > is put on pause we can free unnecessary memory. It will allow, in particular,
> > > > to start relaxing the memory stress on the source host in a load-balancing
> > > > scenario.
> > > >
> > > > Changes from v1:
> > > > - changed name of the interfaces (discard to release)
> > > > - fix make check error
> > > > - add more comments to qemu_iovec_release_ram()
> > > > - rebase on "Postcopy: Hugepage support" (David's patch series)
> > > > - removed ram_discard_page for xbzrle
> > > > - fix erroneous release memory in complete precopy (tie release-ram to postcopy)
> > > >
> > > > Pavel Butsykin (3):
> > > >     migration: add MigrationState arg for ram_save_/compressed_/page()
> > > >     add 'release-ram' migrate capability
> > > >     migration: discard non-dirty ram pages after the start of postcopy
> > > >
> > > >    include/migration/migration.h |  2 ++
> > > >    include/migration/qemu-file.h |  3 ++-
> > > >    migration/migration.c         | 13 ++++++++++
> > > >    migration/qemu-file.c         | 59 
> > > > ++++++++++++++++++++++++++++++++++++++-----
> > > >    migration/ram.c               | 56 ++++++++++++++++++++++++++++++++++------
> > > >    qapi-schema.json              |  5 +++-
> > > >    6 files changed, 121 insertions(+), 17 deletions(-)
> > > >
> > > > --
> > > > 2.11.0
> > > --
> > > Dr. David Alan Gilbert / address@hidden / Manchester, UK
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK