On 06/25/2018 08:05 PM, Wei Wang wrote:
This patch series is separated from the previous "Virtio-balloon
Enhancement" series. The new feature, VIRTIO_BALLOON_F_FREE_PAGE_HINT,
implemented by this series enables the virtio-balloon driver to report
hints of guest free pages to the host. It can be used to accelerate live
migration of VMs. Here is an introduction of this usage:
Live migration needs to transfer the VM's memory from the source machine
to the destination round by round. For the 1st round, all the VM's memory
is transferred. From the 2nd round, only the pieces of memory that were
written by the guest (after the 1st round) are transferred. One method
that is popularly used by the hypervisor to track which part of memory is
written is to write-protect all the guest memory.
This feature enables the optimization by skipping the transfer of guest
free pages during VM live migration. It is not concerned that the memory
pages are used after they are given to the hypervisor as a hint of the
free pages, because they will be tracked by the hypervisor and transferred
in the subsequent round if they are used and written.
* Tests
- Test Environment
Host: Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz
Guest: 8G RAM, 4 vCPU
Migration setup: migrate_set_speed 100G, migrate_set_downtime 2 second
- Test Results
- Idle Guest Live Migration Time (results are averaged over 10 runs):
- Optimization v.s. Legacy = 284ms vs 1757ms --> ~84% reduction
According to Michael's comments, add one more set of data here:
Enabling page poison with value=0, and enable KSM.
The legacy live migration time is 1806ms (averaged across 10 runs),
compared to the case with this optimization feature in use (i.e. 284ms),
there is still around ~84% reduction.
Best,
Wei
