Merge "libvirt: Don't allow "reserving" file-backed memory"

This commit is contained in:
Zuul 2020-06-17 12:41:46 +00:00 committed by Gerrit Code Review
commit 6ed556f4ad
4 changed files with 96 additions and 19 deletions

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@ -46,14 +46,22 @@ Libvirt
capability requires libvirt version 4.4.0 or newer. capability requires libvirt version 4.4.0 or newer.
Qemu Qemu
File-backed memory requires qemu version 2.6.0 or newer.Discard capability File-backed memory requires qemu version 2.6.0 or newer. Discard capability
requires qemu version 2.10.0 or newer. requires qemu version 2.10.0 or newer.
Memory overcommit Memory overcommit
File-backed memory is not compatible with memory overcommit. File-backed memory is not compatible with memory overcommit.
``ram_allocation_ratio`` must be set to ``1.0`` in ``nova.conf``, and the :oslo.config:option:`ram_allocation_ratio` must be set to ``1.0`` in
host must not be added to a :doc:`host aggregate </admin/aggregates>` ``nova.conf``, and the host must not be added to a :doc:`host aggregate
with ``ram_allocation_ratio`` set to anything but ``1.0``. </admin/aggregates>` with ``ram_allocation_ratio`` set to anything but
``1.0``.
Reserved memory
When configured, file-backed memory is reported as total system memory to
placement, with RAM used as cache. Reserved memory corresponds to disk
space not set aside for file-backed memory.
:oslo.config:option:`reserved_host_memory_mb` should be set to ``0`` in
``nova.conf``.
Huge pages Huge pages
File-backed memory is not compatible with huge pages. Instances with huge File-backed memory is not compatible with huge pages. Instances with huge

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@ -1341,6 +1341,39 @@ class LibvirtConnTestCase(test.NoDBTestCase,
self.assertRaises(exception.InternalError, self.assertRaises(exception.InternalError,
drvr._check_file_backed_memory_support) drvr._check_file_backed_memory_support)
def test__check_file_backed_memory_support__total_lt_reserved(self):
"""Ensure an error is raised if total memory < reserved.
Placement won't allow $resource.total < $resource.reserved, so we need
to catch this early.
"""
self.flags(file_backed_memory=1024, group='libvirt')
self.flags(ram_allocation_ratio=1.0, reserved_host_memory_mb=4096)
drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), True)
self.assertRaises(
exception.InternalError, drvr._check_file_backed_memory_support,
)
@mock.patch.object(libvirt_driver.LOG, 'warning')
def test__check_file_backed_memory_support__has_reserved(self, mock_log):
"""Ensure a warning is issued if memory is reserved.
It doesn't make sense to "reserve" memory when file-backed memory is in
use. We should report things so as to avoid confusion.
"""
self.flags(file_backed_memory=8192, group='libvirt')
self.flags(ram_allocation_ratio=1.0)
# we don't need to configure '[DEFAULT] reserved_host_memory_mb' since
# it defaults to 512 (MB)
drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), True)
drvr._check_file_backed_memory_support()
mock_log.assert_called_once()
self.assertIn(
"Reserving memory via '[DEFAULT] reserved_host_memory_mb' is not "
"compatible",
six.text_type(mock_log.call_args[0]),
)
def test__check_cpu_compatibility_start_ok(self): def test__check_cpu_compatibility_start_ok(self):
self.flags(cpu_mode="custom", self.flags(cpu_mode="custom",
cpu_models=["Penryn"], cpu_models=["Penryn"],

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@ -819,22 +819,43 @@ class LibvirtDriver(driver.ComputeDriver):
self._create_new_mediated_device(parent, uuid=mdev_uuid) self._create_new_mediated_device(parent, uuid=mdev_uuid)
def _check_file_backed_memory_support(self): def _check_file_backed_memory_support(self):
if CONF.libvirt.file_backed_memory: if not CONF.libvirt.file_backed_memory:
# file_backed_memory is only compatible with qemu/kvm virts return
if CONF.libvirt.virt_type not in ("qemu", "kvm"):
raise exception.InternalError(
_('Running Nova with file_backed_memory and virt_type '
'%(type)s is not supported. file_backed_memory is only '
'supported with qemu and kvm types.') %
{'type': CONF.libvirt.virt_type})
# file-backed memory doesn't work with memory overcommit. # file_backed_memory is only compatible with qemu/kvm virts
# Block service startup if file-backed memory is enabled and if CONF.libvirt.virt_type not in ("qemu", "kvm"):
# ram_allocation_ratio is not 1.0 raise exception.InternalError(
if CONF.ram_allocation_ratio != 1.0: _('Running Nova with file_backed_memory and virt_type '
raise exception.InternalError( '%(type)s is not supported. file_backed_memory is only '
'Running Nova with file_backed_memory requires ' 'supported with qemu and kvm types.') %
'ram_allocation_ratio configured to 1.0') {'type': CONF.libvirt.virt_type})
# file-backed memory doesn't work with memory overcommit.
# Block service startup if file-backed memory is enabled and
# ram_allocation_ratio is not 1.0
if CONF.ram_allocation_ratio != 1.0:
raise exception.InternalError(
'Running Nova with file_backed_memory requires '
'ram_allocation_ratio configured to 1.0')
if CONF.reserved_host_memory_mb:
# this is a hard failure as placement won't allow total < reserved
if CONF.reserved_host_memory_mb >= CONF.libvirt.file_backed_memory:
msg = _(
"'[libvirt] file_backed_memory', which represents total "
"memory reported to placement, must be greater than "
"reserved memory configured via '[DEFAULT] "
"reserved_host_memory_mb'"
)
raise exception.InternalError(msg)
# TODO(stephenfin): Change this to an exception in W or later
LOG.warning(
"Reserving memory via '[DEFAULT] reserved_host_memory_mb' "
"is not compatible with file-backed memory. Consider "
"setting '[DEFAULT] reserved_host_memory_mb' to 0. This will "
"be an error in a future release."
)
def _check_my_ip(self): def _check_my_ip(self):
ips = compute_utils.get_machine_ips() ips = compute_utils.get_machine_ips()

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@ -0,0 +1,15 @@
---
upgrade:
- |
When using file-backed memory, the ``nova-compute`` service will now fail
to start if the amount of reserved memory configured using ``[DEFAULT]
reserved_host_memory_mb`` is equal to or greater than the total amount of
memory configured using ``[libvirt] file_backed_memory``. Where reserved
memory is less than the total amount of memory configured, a warning will
be raised. This warning will become an error in a future release.
The former combination is invalid as it would suggest reserved memory is
greater than total memory available, while the latter is considered
incorrect behavior as reserving of file-backed memory can and should be
achieved by reducing the filespace allocated as memory by modifying
``[libvirt] file_backed_memory``.