free_disk_gb is not correctly, because swap disk size is not minus.

[Charlotte Han]

1. code in compute/resource_tracker.py

def _update_usage(self, usage, sign=1):
        mem_usage = usage['memory_mb']
        disk_usage = usage.get('root_gb', 0)

        overhead = self.driver.estimate_instance_overhead(usage)
        mem_usage += overhead['memory_mb']
        disk_usage += overhead.get('disk_gb', 0)

        self.compute_node.memory_mb_used += sign * mem_usage
        self.compute_node.local_gb_used += sign * disk_usage
        self.compute_node.local_gb_used += sign * usage.get('ephemeral_gb', 0)
        self.compute_node.vcpus_used += sign * usage.get('vcpus', 0)

        # free ram and disk may be negative, depending on policy:
        self.compute_node.free_ram_mb = (self.compute_node.memory_mb -
                                         self.compute_node.memory_mb_used)
        self.compute_node.free_disk_gb = (self.compute_node.local_gb -
                                          self.compute_node.local_gb_used)

        self.compute_node.running_vms = self.stats.num_instances

2. So I think self.compute_node.local_gb_used is contained swap disk size. And free_disk_gb is not minus swap disk size.

[Maciej Szankin (mszankin)]

Swap partition is a disk space that is not available for storing any kind of data other than memory dumps. So - I think it is perfectly fine to assume that the size of swap sums up with used space.