Re: [Qemu-devel] [PATCH 0/4] Add ignore-external migration capability

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Yury Kotov (yury-kotov@yandex-team.ru) wrote:
> Hi,
> 
> The series adds migration capability which allows to skip 'external' RAM blocks
> during migration. External block is a RAMBlock which available from the outside
> of current QEMU process (e.g. file in /dev/shm). It's useful for fast local
> migration to update QEMU for the running guests.

Hi Yury,
  There have been a few similar patch series around from people wanting
to do similar things.
  In particular Lai Jiangshan's https://lists.nongnu.org/archive/html/qemu-devel/2018-03/msg07511.html
and Cédric Le Goater wanted to skip regions for a different reason.

  We merged some of Cédric's code last year so that we now
have the qemu_ram_is_migratable() function - and we should be reusing
that to skip things rather than adding a new check that we have to add
everywhere.

  Also, ypu're skipping 'external' things, I think the other suggestion
was to skip 'shared' things (i.e. anything with share=0); skipping
share=on cases sounds easier to me.

Dave

> Patches:
> 1. Add offset validation to make sure that external RAM block has the same
>    physical offset on target side,
> 2. Add RAM_EXTERNAL flag to determine external RAM blocks,
> 3. Add ignore-external migration capability,
> 4. Add a test.
> 
> Usage example:
> 1. Start source VM:
>    qemu-system-x86 \
>      -m 4G \
>      -object memory-backend-file,id=mem0,size=4G,share=on,mem-path=/dev/shm/mem0 \
>      -numa node,memdev=mem0 \
>      -qmp unix:/tmp/qemu-qmp-1.sock,server,nowait \
> 
> 2. Start target VM:
>    qemu-system-x86 \
>      -m 4G \
>      -object memory-backend-file,id=mem0,size=4G,share=on,mem-path=/dev/shm/mem0 \
>      -numa node,memdev=mem0 \
>      -qmp unix:/tmp/qemu-qmp-2.sock,server,nowait \
>      -incoming defer
> 
> 3. Enable ignore-external capability on both VMs:
>    { "execute": "migrate-set-capabilities" , "arguments":
>      { "capabilities": [ { "capability": "x-ignore-external", "state": true } ] } }
> 
> 4. Start migration.
> 
> Regards,
> Yury
> 
> Yury Kotov (4):
>   migration: add RAMBlock's offset validation
>   exec: add RAM_EXTERNAL flag to mark non-QEMU allocated blocks
>   migration: introduce ignore-external capability
>   tests/migration-test: Add a test for ignore-external capability
> 
>  backends/hostmem-file.c   |   3 +-
>  exec.c                    |   7 ++-
>  include/exec/cpu-common.h |   1 +
>  include/exec/memory.h     |   3 ++
>  migration/migration.c     |   9 ++++
>  migration/migration.h     |   1 +
>  migration/ram.c           |  52 ++++++++++++++++--
>  numa.c                    |   4 +-
>  qapi/migration.json       |   6 ++-
>  tests/migration-test.c    | 109 +++++++++++++++++++++++++++++++-------
>  10 files changed, 165 insertions(+), 30 deletions(-)
> 
> -- 
> 2.20.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK