我跑虚机8G，里面要跑1个512M，还说 Cannot allocate memory？？

[root@block1 nova(keystone_admin)]# tail 200 nova-compute.log
tail: cannot open 00for reading: No such file or directory
==> nova-compute.log <==
2018-03-06 00:08:29.426 3115 ERROR oslo_messaging.rpc.server   File "/usr/lib64/python2.7/site-packages/libvirt.py", line 1065, in createWithFlags
2018-03-06 00:08:29.426 3115 ERROR oslo_messaging.rpc.server     if ret == -1: raise libvirtError ('virDomainCreateWithFlags() failed', dom=self)
2018-03-06 00:08:29.426 3115 ERROR oslo_messaging.rpc.server libvirtError: internal error: qemu unexpectedly closed the monitor: 2018-03-05T16:08:26.557797Z qemu-kvm: cannot set up guest memory 'pc.ram': Cannot allocate memory
2018-03-06 00:08:29.426 3115 ERROR oslo_messaging.rpc.server
2018-03-06 00:08:57.819 3115 INFO nova.compute.resource_tracker [req-d7a8bdab-245d-48ab-981b-56ce4c676e6f - - - - -] Final resource view: name=block1 phys_ram=8191MB used_ram=1024MB phys_disk=19GB used_disk=1GB total_vcpus=2 used_vcpus=1 pci_stats=[]
2018-03-06 00:09:59.825 3115 INFO nova.compute.resource_tracker [req-d7a8bdab-245d-48ab-981b-56ce4c676e6f - - - - -] Final resource view: name=block1 phys_ram=8191MB used_ram=1024MB phys_disk=19GB used_disk=1GB total_vcpus=2 used_vcpus=1 pci_stats=[]
2018-03-06 00:10:59.768 3115 INFO nova.compute.resource_tracker [req-d7a8bdab-245d-48ab-981b-56ce4c676e6f - - - - -] Final resource view: name=block1 phys_ram=8191MB used_ram=1024MB phys_disk=19GB used_disk=1GB total_vcpus=2 used_vcpus=1 pci_stats=[]
2018-03-06 00:11:35.158 3115 WARNING nova.compute.manager [req-d7a8bdab-245d-48ab-981b-56ce4c676e6f - - - - -] While synchronizing instance power states, found 1 instances in the database and 0 instances on the hypervisor.
2018-03-06 00:11:35.280 3115 INFO nova.compute.manager [-] [instance: 2211b3ec-5d39-4752-94b4-a38206f7c009] During _sync_instance_power_state the DB power_state (4) does not match the vm_power_state from the hypervisor (0). Updating power_state in the DB to match the hypervisor.
2018-03-06 00:12:00.135 3115 INFO nova.compute.resource_tracker [req-d7a8bdab-245d-48ab-981b-56ce4c676e6f - - - - -] Final resource view: name=block1 phys_ram=8191MB used_ram=1024MB phys_disk=19GB used_disk=1GB total_vcpus=2 used_vcpus=1 pci_stats=[]
[root@block1 nova(keystone_admin)]#

2018-03-06 00:10:59.768 3115 INFO nova.compute.resource_tracker [req-d7a8bdab-245d-48ab-981b-56ce4c676e6f - - - - -] Final resource view: name=block1 phys_ram=8191MB used_ram=1024MB phys_disk=19GB used_disk=1GB total_vcpus=2 used_vcpus=1 pci_stats=[]
上面有信息显示：ram 1024m,也就是需要1G