On 22.07.2020 18:42, Denis Plotnikov wrote:
On 22.07.2020 17:50, Peter Xu wrote:
Hi, Denis,
Hi, Peter
...
How to use:
1. enable background snapshot capability
virsh qemu-monitor-command vm --hmp migrate_set_capability
background-snapshot on
2. stop the vm
virsh qemu-monitor-command vm --hmp stop
3. Start the external migration to a file
virsh qemu-monitor-command cent78-bs --hmp migrate exec:'cat >
./vm_state'
4. Wait for the migration finish and check that the migration has
completed state.
Thanks for continued working on this project! I have two high level
questions
before dig into the patches.
Firstly, is step 2 required? Can we use a single QMP command to take
snapshots
(which can still be a "migrate" command)?
With this series it is required, but steps 2 and 3 should be merged
into a single one.
Meanwhile, we might also want to check around the type of backend
RAM. E.g.,
shmem and hugetlbfs are still not supported for uffd-wp (which I'm still
working on). I didn't check explicitly whether we'll simply fail the
migration
for those cases since the uffd ioctls will fail for those kinds of
RAM. It
would be okay if we handle all the ioctl failures gracefully,
The ioctl's result is processed but the patch has a flaw - it ignores
the result of ioctl check. Need to fix it.
It happens here:
+int ram_write_tracking_start(void)
+{
+ if (page_fault_thread_start()) {
+ return -1;
+ }
+
+ ram_block_list_create();
+ ram_block_list_set_readonly(); << this returns -1 in case of failure but I
just ignore it here
+
+ return 0;
+}
or it would be
even better if we directly fail when we want to enable live snapshot
capability
for a guest who contains other types of ram besides private anonymous
memories.
I agree, but to know whether shmem or hugetlbfs are supported by the
current kernel we should
execute the ioctl for all memory regions on the capability enabling.
Thanks,
Denis