On 06.07.23 10:15, Juan Quintela wrote:
David Hildenbrand <da...@redhat.com> wrote:
Already when starting QEMU we perform one system reset that ends up
triggering virtio_mem_unplug_all() with no actual memory plugged yet.
That, in turn will trigger ram_block_discard_range() and perform some
other actions that are not required in that case.
Let's optimize virtio_mem_unplug_all() for the case that no memory is
plugged. This will be beneficial for x-ignore-shared support as well.
Tested-by: Mario Casquero <mcasq...@redhat.com>
Signed-off-by: David Hildenbrand <da...@redhat.com>
It works, so ...
Reviewed-by: Juan Quintela <quint...@redhat.com>
Thanks!
[...]
+ bitmap_clear(vmem->bitmap, 0, vmem->bitmap_size);
vmem->size = 0;
notifier_list_notify(&vmem->size_change_notifiers, &vmem->size);
}
+
trace_virtio_mem_unplugged_all();
virtio_mem_resize_usable_region(vmem, vmem->requested_size, true);
return 0;
Once that we are here. Do you remember _why_ do we allow virtio-mem
plug/unplug in the middle of a migration.
We forbid to plug/unplug everything else. Why do we need to plug/unplug
virtio-mem during migration?
With virtio-mem you tell the VM the desired size for the device
(requested-size), and the VM will select blocks to (un)plug and send
(un)plug requests to the hypervisor in order to reach the requested size.
So changing the requested size in the hypervisor (by the QEMU user) and
the VM processing that resize request is asynchronous -- similar to
memory ballooning.
As the VM can send these (un)plug requests any time, and we exactly
don't want to allow (un)plug during migration, we have
virtio_mem_is_busy() to reject any such requests to tell the VM "please
try again later".
--
Cheers,
David / dhildenb
