Re: [PATCH] bugfix:migrate with block-dirty-bitmap (disk size is big enough) can't be finished

[Vladimir Sementsov-Ogievskiy]

On 9/10/22 09:35, liuhaiwei wrote:
> From: liuhaiwei <liuhaiwei@inspur.com>
>
> bug description as  https://gitlab.com/qemu-project/qemu/-/issues/1203
> Usually,we use the precopy or postcopy mode to migrate block dirty bitmap.
> but if block-dirty-bitmap size more than threshold size,we cannot entry the 
> migration_completion in migration_iteration_run function
> To solve this problem, we can setting  the pending size to a fake 
> value(threshold-1 or 0) to tell  migration_iteration_run function to entry the 
> migration_completion,if pending size > threshold size


Actually, bitmaps migrate in postcopy. So, you should start postcopy for it to work (qmp 
command migrate-start-postcopy). This command simply set the boolean variable, so that in 
migration_iteration_run() we'll move to postcopy when needed. So, you can start this 
command immediately after migrate command, or even before it, but after setting the 
"dirty-bitmaps" capability.

Fake pending is a wrong thing to do, it means that you will make downtime to be 
larger than expected.

--
Best regards,
Vladimir