[PATCH v3 0/4] Allow to enable multifd and postcopy migration together

[Prasad Pandit <ppandit@redhat.com>]

From: Prasad Pandit <pjp@fedoraproject.org>

Hello,

* Currently Multifd and Postcopy migration can not be used together.
  QEMU shows "Postcopy is not yet compatible with multifd" message.

  When migrating guests with large (100's GB) RAM, Multifd threads
  help to accelerate migration, but inability to use it with the
  Postcopy mode delays guest start up on the destination side.

* This patch series allows to enable both Multifd and Postcopy
  migration together. Precopy and Multifd threads work during
  the initial guest (RAM) transfer. When migration moves to the
  Postcopy phase, Multifd threads are restrained and the Postcopy
  threads start to request pages from the source side.

* This series removes magic value (4-bytes) introduced in the
  previous series for the Postcopy channel. And refactoring of
  the 'ram_save_target_page' function is made independent of
  the multifd & postcopy change.

* This series passes all existing 'tests/qtest/migration/*' test
  cases and adds a new one to enable multifd channels with postcopy
  migration.

  v2: https://lore.kernel.org/qemu-devel/20241129122256.96778-1-ppandit@redhat.com/T/#u
  v1: https://lore.kernel.org/qemu-devel/20241126115748.118683-1-ppandit@redhat.com/T/#u
  v0: https://lore.kernel.org/qemu-devel/20241029150908.1136894-1-ppandit@redhat.com/T/#u


Thank you.
---
Prasad Pandit (4):
  migration/multifd: move macros to multifd header
  migration: refactor ram_save_target_page functions
  migration: enable multifd and postcopy together
  tests/qtest/migration: add postcopy test with multifd

 migration/migration.c                  | 106 +++++++++++++++----------
 migration/multifd-nocomp.c             |   3 +-
 migration/multifd.c                    |   5 --
 migration/multifd.h                    |   5 ++
 migration/options.c                    |   5 --
 migration/ram.c                        |  69 +++++-----------
 tests/qtest/migration/framework.c      |   8 ++
 tests/qtest/migration/framework.h      |   3 +
 tests/qtest/migration/postcopy-tests.c |  10 +++
 9 files changed, 112 insertions(+), 102 deletions(-)

--
2.48.1