[PATCH v5 00/23] migration: File based migration with multifd and mapped-ram

[Fabiano Rosas]

Based-on: 74aa0fb297 (migration: options incompatible with cpr) # 
peterx/migration-next

Hi,

In this v5:

- Rebased on migration-next;

- Renamed the feature to mapped-ram;

- Reworked recv_sync logic to only sync at RAM_SAVE_FLAG_MEM_SIZE and
  ignore/avoid all other RAM_FLAGS;

- Fixed and documented barriers at multifd_recv/multifd_recv_thread;

- Duplicated fds passed to multifd to avoid cross-channel effects;

- Dropped the direct-io and fdset patches. Will send them in a
  separate series.

The rest are minor changes, I have noted them in the patches
themselves.

CI run: https://gitlab.com/farosas/qemu/-/pipelines/1194172845

Series structure
================

This series enables mapped-ram in steps:

0) Cleanups                           [1]
1) QIOChannel interfaces              [2-6]
2) Mapped-ram format for precopy      [7-11]
3) Multifd adaptation without packets [12-15]
4) Mapped-ram format for multifd      [16-23]

* below will be sent separately *
5) Direct-io generic support          [TODO]
6) Direct-io for mapped-ram multifd with file: URI  [TODO]
7) Fdset interface for mapped-ram multifd  [TODO]

About mapped-ram
================

Mapped-ram is a new stream format for the RAM section designed to
supplement the existing ``file:`` migration and make it compatible
with ``multifd``. This enables parallel migration of a guest's RAM to
a file.

The core of the feature is to map RAM pages to migration file
offsets. This enables the ``multifd`` threads to write exclusively to
those offsets even if the guest is constantly dirtying pages
(i.e. live migration).

Another benefit is that the resulting file will have a bounded size,
since pages which are dirtied multiple times will always go to a fixed
location in the file, rather than constantly being added to a
sequential stream.

Having the pages at fixed offsets also allows the usage of O_DIRECT
for save/restore of the migration stream as the pages are ensured to
be written respecting O_DIRECT alignment restrictions.

Latest numbers (unchanged from v4)
==============

=> guest: 128 GB RAM - 120 GB dirty - 1 vcpu in tight loop dirtying memory
=> host: 128 CPU AMD EPYC 7543 - 2 NVMe disks in RAID0 (8586 MiB/s) - xfs
=> pinned vcpus w/ NUMA shortest distances - average of 3 runs - results
   from query-migrate

non-live           | time (ms)   pages/s   mb/s   MB/s
-------------------+-----------------------------------
file               |    110512    256258   9549   1193
  + bg-snapshot    |    245660    119581   4303    537
-------------------+-----------------------------------
mapped-ram         |    157975    216877   6672    834
  + multifd 8 ch.  |     95922    292178  10982   1372
     + direct-io   |     23268   1936897  45330   5666
-------------------------------------------------------

live               | time (ms)   pages/s   mb/s   MB/s
-------------------+-----------------------------------
file               |         -         -      -      - (file grew 4x the VM 
size)
  + bg-snapshot    |    357635    141747   2974    371
-------------------+-----------------------------------
mapped-ram         |         -         -      -      - (no convergence in 5 min)
  + multifd 8 ch.  |    230812    497551  14900   1862
     + direct-io   |     27475   1788025  46736   5842
-------------------------------------------------------

v4:
20240220224138.24759-1-farosas@suse.de">https://lore.kernel.org/r/20240220224138.24759-1-farosas@suse.de
v3:
https://lore.kernel.org/r/20231127202612.23012-1-farosas@suse.de
v2:
https://lore.kernel.org/r/20231023203608.26370-1-farosas@suse.de
v1:
https://lore.kernel.org/r/20230330180336.2791-1-farosas@suse.de

Fabiano Rosas (20):
  migration/multifd: Cleanup multifd_recv_sync_main
  io: fsync before closing a file channel
  migration/qemu-file: add utility methods for working with seekable
    channels
  migration/ram: Introduce 'mapped-ram' migration capability
  migration: Add mapped-ram URI compatibility check
  migration/ram: Add outgoing 'mapped-ram' migration
  migration/ram: Add incoming 'mapped-ram' migration
  tests/qtest/migration: Add tests for mapped-ram file-based migration
  migration/multifd: Rename MultiFDSend|RecvParams::data to
    compress_data
  migration/multifd: Decouple recv method from pages
  migration/multifd: Allow multifd without packets
  migration/multifd: Allow receiving pages without packets
  migration/multifd: Add a wrapper for channels_created
  migration/multifd: Add outgoing QIOChannelFile support
  migration/multifd: Add incoming QIOChannelFile support
  migration/multifd: Prepare multifd sync for mapped-ram migration
  migration/multifd: Support outgoing mapped-ram stream format
  migration/multifd: Support incoming mapped-ram stream format
  migration/multifd: Add mapped-ram support to fd: URI
  tests/qtest/migration: Add a multifd + mapped-ram migration test

Nikolay Borisov (3):
  io: add and implement QIO_CHANNEL_FEATURE_SEEKABLE for channel file
  io: Add generic pwritev/preadv interface
  io: implement io_pwritev/preadv for QIOChannelFile

 docs/devel/migration/features.rst   |   1 +
 docs/devel/migration/mapped-ram.rst | 138 ++++++++++
 include/exec/ramblock.h             |  13 +
 include/io/channel.h                |  83 ++++++
 include/migration/qemu-file-types.h |   2 +
 include/qemu/bitops.h               |  13 +
 io/channel-file.c                   |  69 +++++
 io/channel.c                        |  58 ++++
 migration/fd.c                      |  44 +++
 migration/fd.h                      |   2 +
 migration/file.c                    | 153 ++++++++++-
 migration/file.h                    |   8 +
 migration/migration.c               |  56 +++-
 migration/multifd-zlib.c            |  26 +-
 migration/multifd-zstd.c            |  26 +-
 migration/multifd.c                 | 405 ++++++++++++++++++++++------
 migration/multifd.h                 |  27 +-
 migration/options.c                 |  35 +++
 migration/options.h                 |   1 +
 migration/qemu-file.c               | 106 ++++++++
 migration/qemu-file.h               |   6 +
 migration/ram.c                     | 333 +++++++++++++++++++++--
 migration/ram.h                     |   1 +
 migration/savevm.c                  |   1 +
 migration/trace-events              |   2 +-
 qapi/migration.json                 |   6 +-
 tests/qtest/migration-test.c        | 127 +++++++++
 27 files changed, 1600 insertions(+), 142 deletions(-)
 create mode 100644 docs/devel/migration/mapped-ram.rst

-- 
2.35.3