Re: [Qemu-devel] [PATCH v5 00/12] Dirty bitmaps migration

["Denis V. Lunev" <den@openvz.org>]

On 21/05/15 16:51, Vladimir Sementsov-Ogievskiy wrote:
> Hi all.
>
> Hmm. There is an interesting suggestion from Denis Lunev (in CC) about 
> how to drop meta bitmaps and make things easer.
>
> method:
>
> > start migration
> disk and memory are migrated, but not dirty bitmaps.
> > stop vm
> create all necessary bitmaps in destination vm (empty, but with same 
> names and granularities and enabled flag)
> > start destination vm
> empty bitmaps are tracking now
> > start migrating dirty bitmaps. merge them to corresponding bitmaps 
> in destination
> while bitmaps are migrating, they should be in some kind of 
> 'inconsistent' state.
> so, we can't start backup or other migration while bitmaps are 
> migrating, but vm is already _running_ on destination.
>
> what do you think about it?
>

the description is a bit incorrect

- start migration process, perform memory and disk migration
    as usual. VM is still executed at source
- start VM on target. VM on source should be on pause as usual,
    do not finish migration process. Running VM on target "writes"
    normally setting dirty bits as usual
- copy active dirty bitmaps from source to target. This is safe
    as VM on source is not running
- "OR" copied bitmaps with ones running on target
- finish migration process (stop source VM).

Downtime will not be increased due to dirty bitmaps with this
approach, migration process is very simple - plain data copy.

Regards,
     Den

> On 13.05.2015 18:29, Vladimir Sementsov-Ogievskiy wrote:
>> These patches provide dirty bitmap migration feature. Only named dirty
>> bitmaps are to be migrated. Migration may be enabled using migration
>> capabilities.
>>
>> v5:
>>      - rebase on master
>>      - drop [PATCH RFC v4 10/13] iotests: add event_wait to VM class
>>      - remove rfc, as incremental backup series by John Snow are in
>>        upstream
>>
>> v4 significant changes:
>>   0001: tiny bugfix: out[i] -> out[i-start], same for 'in'
>>   0007: set chunk size to 1kb, disable live iteration for
>>         migrating data < 1mb size.
>>
>>   tests: only one with md5 sum is here. used function event_wait
>>          by John Snow. (I hope, you don't mind me just adding this
>>          function with your 'Signed-off-by')
>>
>>   rfc: This patch set is based on v13 of
>>        "block: incremental backup series" by John Snow, which are
>>        not pushed yet.
>>
>> v3:
>>   based on v13 of "block: incremental backup series" by John Snow.
>>
>>   changes from v2:
>>   removed patch for adding dirty parameter (migration capablities used
>>   instead).
>>     0001: printf's dropped, qapi used
>>   0002: part0 -> zeroes
>>   0003: part0 -> zeroes
>>   0005: dirty_dirty -> meta
>>         add comments about meta bitmap
>>           0006: the format is changed, nodes used instead of devices.
>>
>>   other patches are new.
>>
>>   rfc: there are two tests. They are the same but using different
>>   interfaces: md5 checksum of the bitmap last layer in query-block or
>>   separate query-block-dirty-bitmap with dirty bitmap regions.
>>   The second form is more appropriate for debugging, the first is more
>>   appropriate for simple regression control. Which should go to
>>   upstream?
>>
>> v2:
>>   1. bug-fixes, that are already in upstream, and renaming of function
>>   bdrv_reset_dirty_bitmap (which is already in Snow's series) are
>>   dropped
>>   2. bitmap store/restore: the concept renamed to serialization, added
>>   function hbitmap_deserialize_part0, to not transfer zero blocks
>>   3. migration dirty parameter: added description comment
>>   4. Other patches are new.
>>
>> v2.rfc:
>> Actually, in this version of the series I'm trying not use
>> migration/block.c at all. Instead a separate migration unit is added
>> in the new file migration/dirty-bitmap.c. Now bitmaps are migrated
>> like blocks in block migration, they have their "dirty-dirty" bitmaps,
>> for tracking set/unset changes during migration.
>>
>> The advantages are:
>>    - no complications of migration/block.c
>>    - separate dirty-dirty bitmaps provide handling of "unset's"
>>    - more effective meta-data/data ratio - no tiny bitmap-blocks.
>>
>>
>>
>> v1:
>> These patches provide dirty bitmap migration feature. Only named dirty
>> bitmaps are to be migrated. Migration is made as a part of block
>> migration in block-migration.c.
>>
>> Dirty bitmap migration may be enabled by "dirty" parameter for qmp 
>> migrate
>> command. If "blk" and "inc" parameters are false when "dirty" is true
>> block migration is actually skipped: no allocatoions, no bdrv_read's,
>> no bdrv_write's, only bitmaps are migrated.
>>
>> The patch set includes two my previous bug fixes, which are necessary
>> for it. The patch set is based on Incremental backup series by John
>> Snow.
>> Vladimir Sementsov-Ogievskiy (12):
>>    hbitmap: serialization
>>    block: BdrvDirtyBitmap serialization interface
>>    block: tiny refactoring: minimize hbitmap_(set/reset) usage
>>    block: add meta bitmaps
>>    block: add bdrv_next_dirty_bitmap()
>>    qapi: add dirty-bitmaps migration capability
>>    migration: add migration/block-dirty-bitmap.c
>>    iotests: maintain several vms in test
>>    iotests: add add_incoming_migration to VM class
>>    qapi: add md5 checksum of last dirty bitmap level to query-block
>>    iotests: add dirty bitmap migration test
>>    migration/qemu-file: make functions qemu_(get/put)_string public
>>
>>   block.c                        |  98 +++++-
>>   include/block/block.h          |  22 ++
>>   include/migration/block.h      |   1 +
>>   include/migration/migration.h  |   1 +
>>   include/migration/qemu-file.h  |  17 +
>>   include/qemu/hbitmap.h         |  67 ++++
>>   migration/Makefile.objs        |   2 +-
>>   migration/block-dirty-bitmap.c | 693 
>> +++++++++++++++++++++++++++++++++++++++++
>>   migration/migration.c          |   9 +
>>   migration/qemu-file.c          |  18 ++
>>   qapi-schema.json               |   4 +-
>>   qapi/block-core.json           |   4 +-
>>   tests/qemu-iotests/117         |  84 +++++
>>   tests/qemu-iotests/117.out     |   5 +
>>   tests/qemu-iotests/group       |   1 +
>>   tests/qemu-iotests/iotests.py  |  14 +-
>>   util/hbitmap.c                 | 106 +++++++
>>   vl.c                           |   1 +
>>   18 files changed, 1137 insertions(+), 10 deletions(-)
>>   create mode 100644 migration/block-dirty-bitmap.c
>>   create mode 100755 tests/qemu-iotests/117
>>   create mode 100644 tests/qemu-iotests/117.out
>>
>
>