Enable charm to configure mds cache options.

Closes-Bug: #1891409
Func-Test-PR: https://github.com/openstack-charmers/zaza-openstack-tests/pull/774
Change-Id: If2bdd5c0f2afa1843e686cf69570a50901c85875

src/config.yaml

@@ -258,3 +258,24 @@ options:
     description: |
       Value of bluestore compression max blob size for solid state media on
       pools requested by this charm.
+  mds-cache-memory-limit:
+    type: string
+    default: 4Gi
+    description: |
+      Set the maximum size of Metadata Server (MDS) cache, in bytes. The MDS
+      will try to stay under this value by (1 - mds_cache_reservation) as a
+      percent. This is not a hard limit.
+  mds-cache-reservation:
+    type: float
+    default: 0.05
+    description: |
+      The cache reservation for the MDS cache to maintain. The MDS will try
+      to stay under this value as a percent by (1 - mds_cache_reservation)
+      as a percent.
+  mds-health-cache-threshold:
+    type: float
+    default: 1.5
+    description: |
+      If the MDS exceeds the cache size specified in mds-cache-memory-limit,
+      this parameter sets the memory limit, as a percentage of
+      mds_cache_reservation, that triggers a health warning.

src/lib/charm/openstack/ceph_fs.py

@@ -53,6 +53,10 @@ class CephFSCharmConfigurationAdapter(
     def networks(self):
         return self.charm_instance.get_networks('ceph-public-network')
 
+    @property
+    def mds_cache(self):
+        return self.charm_instance.get_mds_cache()
+
     @property
     def public_addr(self):
         if ch_core.hookenv.config('prefer-ipv6'):
@@ -119,6 +123,13 @@ class BaseCephFSCharm(charms_openstack.plugins.CephCharm):
 
         return self.get_host_ip()
 
+    def get_mds_cache(self):
+        return {'mds-cache-memory-limit': config('mds-cache-memory-limit'),
+                'mds-cache-reservation': config('mds-cache-reservation'),
+                'mds-health-cache-threshold':
+                config('mds-health-cache-threshold')
+                }
+
     @cached
     @staticmethod
     def get_host_ip(hostname=None):

src/templates/ceph.conf

@@ -26,6 +26,9 @@ log file = /var/log/ceph.log
 
 [mds]
 keyring = /var/lib/ceph/mds/$cluster-$id/keyring
+mds cache memory limit = {{ options.mds_cache_memory_limit }}
+mds cache reservation = {{ options.mds_cache_reservation }}
+mds health cache threshold = {{ options.mds_health_cache_threshold }}
 
 [mds.{{ options.mds_name }}]
 host = {{ options.hostname }}

unit_tests/test_lib_charm_openstack_ceph_fs.py

@@ -80,3 +80,12 @@ class TestCephFsCharm(test_utils.PatchHelper):
         self.assertEquals(
             self.target.options.public_addr,
             '2001:db8::fake')
+        self.patch_target('get_mds_cache')
+        self.get_mds_cache.return_value = {
+            'mds-cache-memory-limit': '4Gi',
+            'mds-cache-reservation': 0.05,
+            'mds-health-cache-threshold': 1.5}
+        self.assertEquals(self.target.options.mds_cache, {
+            'mds-cache-memory-limit': '4Gi',
+            'mds-cache-reservation': 0.05,
+            'mds-health-cache-threshold': 1.5})