[Qemu-devel] [Bug]? (RDMA-related) ballooned memory not consulted during migration?

[Michael R. Hines]

Consider the following sequence:

1. Boot fresh VM (say, a boring 1GB vm)                    => Resident 
set is small, say 100M
2. Touch all the memory (with a utility or something) => Resident set is ~1G
3. Send QMP "balloon 500" => Resident set is ~500M
4. Now, migrate the VM => Resident set is 1G again

This suggests to me that migration is not accounting for
what memory was ballooned.

I suspect this is because the migration_bitmap does not coordinate
with the list of ballooned-out memory that was MADVISED().

This affects RDMA as well as TCP on the sender side.

Is there any hard reason why we're not validating migration_bitmap against
the memory that was MADVISED()'d?

- Michael R. Hines