Re: [Qemu-devel] [PATCH 00/18] Dirty bitmaps postcopy migration

[Dr. David Alan Gilbert]

* Vladimir Sementsov-Ogievskiy (address@hidden) wrote:
> v2:
> some bugs fixed, iotests a bit changed and merged into one test.
> based on block-next (https://github.com/XanClic/qemu/commits/block-next)
> clone: tag postcopy-v2 from https://src.openvz.org/scm/~vsementsov/qemu.git
> online: 
> https://src.openvz.org/users/vsementsov/repos/qemu/browse?at=refs%2Ftags%2Fpostcopy-v2
> 
> v1:
> 
> These series are derived from my 'Dirty bitmaps migration' series. The
> core idea is switch to postcopy migration and drop usage of meta
> bitmaps.
> 
> These patches provide dirty bitmap postcopy migration feature. Only
> named dirty bitmaps are to be migrated. Migration may be enabled using
> migration capabilities.
> 
> The overall method (thanks to John Snow):
> 
> 1. migrate bitmaps meta data in .save_live_setup
>    - create/find related bitmaps on target
>    - disable them
>    - create successors (anonimous children) only for enabled migrated
>      bitmaps
> 2. do nothing in precopy stage
> 3. just before target vm start: enable successors, created in (1)
> 4. migrate bitmap data
> 5. reclaime bitmaps (merge successors to their parents)
> 6. enable bitmaps (only bitmaps, which was enabled in source)

I'd like to just understand a little bit more about the structure;
    a)I don't see anything where the destination asks the source for data;
      am I right or just missing that?
    b)If I'm right about (a) is the only reason it's called 'postcopy'
      because it's done when the destination is already running?
    c)How does it play together with ram postcopy; do they get in each
      others way?

Dave

> 
> Some patches are unchnaged from (v7) of 'Dirty bitmaps migration'
> (DBMv7). I've left Reviewed-by's for them, if you don't like it, say me
> and I'll drop them in the following version.
> 
> So, relatively to last DBMv7: 
> 
> 01-04: new patches, splitting common postcopy migration out of ram
>        postcopy migration
>    05: equal to DBMv7.05
>    06: new
>    07: equal to DBMv7.06
>    08: new
>    09: equal to DBMv7.07
>    10: new
>    11: derived from DBMv7.08, see below
> 12-15: equal to DBMv7.09-12
>    16: derived from DBMv7.13
>        - switch from fifo to socket, as postcopy don't work with fifo
>          for now
>        - change parameters: size, granularity, regions
>        - add time.sleep, to wait for postcopy migration phase (bad
>          temporary solution.
>        - drop Reviewed-by
>    17: new
> 
>    11: the core patch of the series, it is derived from
>        [DBMv7.08: migration: add migration_block-dirty-bitmap.c]
>        There are a lot of changes related to switching from precopy to
>        postcopy, but functions related to migration stream itself
>        (structs, send/load sequences) are mostly unchnaged.
> 
>        So, changes, to switch from precopy to postcopy:
>        - removed all staff related to meta bitmaps and dirty phase!!!
>        - add dirty_bitmap_mig_enable_successors, and call it before
>          target vm start in loadvm_postcopy_handle_run
>        - add enabled_bitmaps list of bitmaps for
>          dirty_bitmap_mig_enable_successors
> 
>        - enabled flag is send with start bitmap chunk instead of
>          completion chunk
>        - sectors_per_chunk is calculated directly from CHUNK_SIZE, not
>          using meta bitmap granularity
> 
>        - dirty_bitmap_save_iterate: remove dirty_phase, move bulk_phase
>          to postcopy stage
>        - dirty_bitmap_save_pending: remove dirty phase related pending,
>          switch pending to non-postcopyable
>        - dirty_bitmap_load_start: get enabled flag and prepare
>          successors for enabled bitmaps, also add them to
>          enabled_bitmaps list
>        - dirty_bitmap_load_complete: for enabled bitmaps: merge them
>          with successors and enable
> 
>        - savevm handlers:
>          * remove separate savevm_dirty_bitmap_live_iterate_handlers state
>            (it was bad idea, any way), and move its save_live_iterate to
>            savevm_dirty_bitmap_handlers
>          * add is_active_iterate savevm handler, which allows iterations
>            only in postcopy stage (after stopping source vm)
>          * add has_postcopy savevm handler. (ofcourse, just returning true)
>          * use save_live_complete_postcopy instead of
>            save_live_complete_precopy
> 
>        Other changes:
>        - some debug output changed
>        - remove MIN_LIVE_SIZE, is_live_iterative and related staff (it
>          was needed to omit iterations if bitmap data is small, possibly
>          this should be reimplemented)
> 
> Vladimir Sementsov-Ogievskiy (18):
>   migration: add has_postcopy savevm handler
>   migration: fix ram_save_pending
>   migration: split common postcopy out of ram postcopy
>   migration: introduce postcopy-only pending
>   block: add bdrv_next_dirty_bitmap()
>   block: add bdrv_dirty_bitmap_enable_successor()
>   qapi: add dirty-bitmaps migration capability
>   block/dirty-bitmap: add bdrv_dirty_bitmap_release_successor
>   migration: include migrate_dirty_bitmaps in migrate_postcopy
>   migration/qemu-file: add qemu_put_counted_string()
>   migration: add is_active_iterate handler
>   migration: add postcopy migration of dirty bitmaps
>   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 default node-name
>   iotests: add dirty bitmap migration test 117
>   iotests: add dirty bitmap postcopy test
> 
>  block/dirty-bitmap.c           |  26 ++
>  include/block/dirty-bitmap.h   |   6 +
>  include/migration/block.h      |   1 +
>  include/migration/migration.h  |   6 +
>  include/migration/qemu-file.h  |   2 +
>  include/migration/vmstate.h    |   7 +-
>  include/qemu/hbitmap.h         |   8 +
>  include/sysemu/sysemu.h        |   5 +-
>  migration/Makefile.objs        |   2 +-
>  migration/block-dirty-bitmap.c | 699 
> +++++++++++++++++++++++++++++++++++++++++
>  migration/block.c              |   7 +-
>  migration/migration.c          |  66 ++--
>  migration/postcopy-ram.c       |   4 +-
>  migration/qemu-file.c          |  13 +
>  migration/ram.c                |  19 +-
>  migration/savevm.c             |  56 +++-
>  migration/trace-events         |   2 +-
>  qapi-schema.json               |   4 +-
>  qapi/block-core.json           |   5 +-
>  tests/qemu-iotests/169         | 134 ++++++++
>  tests/qemu-iotests/169.out     |   5 +
>  tests/qemu-iotests/group       |   2 +
>  tests/qemu-iotests/iotests.py  |  21 +-
>  util/hbitmap.c                 |   8 +
>  vl.c                           |   1 +
>  25 files changed, 1055 insertions(+), 54 deletions(-)
>  create mode 100644 migration/block-dirty-bitmap.c
>  create mode 100755 tests/qemu-iotests/169
>  create mode 100644 tests/qemu-iotests/169.out
> 
> -- 
> 1.8.3.1
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK