devel/migration/postcopy.rst

7 'Postcopy' migration is a way to deal with migrations that refuse to converge
9 the amount of migration traffic and time it takes, the down side is that during
16 Postcopy can be combined with precopy (i.e. normal migration) so that if precopy
23 destination) prior to the start of migration:
27 The normal commands are then used to start a migration, which is still
33 It can be issued immediately after migration is started or any
34 time later on.  Issuing it after the end of a migration is harmless.
36 Blocktime is a postcopy live migration metric, intended to show how
66     Set at the start of migration if postcopy is enabled, even
70     The destination will fail early in migration at this point if the
87     pages off the migration stream, while the main thread carries
97     thread now finishes processing the migration package and
98     now carries on as it would for normal precopy migration
100     finishes a normal migration).
104     The listen thread can now quit, and perform the cleanup of migration
105     state, the migration is now complete.
112 the migration stream has to be able to respond with page data *during* the
120 Until postcopy is entered the migration stream is identical to normal
134 contents are formatted in the same way as the main migration stream.
148 reading the migration stream; the 'postcopy advise' and 'discard' commands
175    a new thread (a) is started that takes over servicing the migration stream,
185    is no longer used by migration, while the listen thread carries on servicing
186    page data until the end of migration.
191 The 'migration bitmap' in postcopy is basically the same as in the precopy,
206 fail a migration because VM data resides in both source and destination
209 paused postcopy migration.
214     migration state.
217     can setup the new channel for migration using QMP command
221     migration using QMP command 'migrate' with resume=true flag set.
228     the two QEMUs to continue the postcopy migration.  For example, there
234     postcopy migration on both sides and go back to **POSTCOPY_ACTIVE**
235     state.  Postcopy migration will continue.
237 During a paused postcopy migration, the VM can logically still continue
268 Postcopy migration with shared memory needs explicit support from the other
312 the background migration channel.  Anyone who cares about latencies of page
313 faults during a postcopy migration should enable this feature.  By default,