ducktape: Increase partition density in the MPT

Increase partition density to 2k partitions per shard and adapt the test
to use the new memory group aware config.

tests/rptest/scale_tests/many_partitions_test.py

@@ -43,12 +43,16 @@
 BIG_FETCH = 104857600
 
 # How much memory to assign to redpanda per partition. Redpanda will be started
-# with MIB_PER_PARTITION * PARTITIONS_PER_SHARD * CORE_COUNT memory
-DEFAULT_MIB_PER_PARTITION = 4
+# with (MIB_PER_PARTITION * PARTITIONS_PER_SHARD * CORE_COUNT) / (PARTITIONS_MEMORY_ALLOCATION_PERCENT / 100) memory
+DEFAULT_MIB_PER_PARTITION = 0.2
 
 # How many partitions we will create per shard: this is the primary scaling
 # factor that controls how many partitions a given cluster will get.
-DEFAULT_PARTITIONS_PER_SHARD = 1000
+DEFAULT_PARTITIONS_PER_SHARD = 2000
+
+# How much memory is reserved for partitions
+# aka: topic_partitions_memory_allocation_percent config
+DEFAULT_PARTITIONS_MEMORY_ALLOCATION_PERCENT = 10
 
 # Large volume of data to write. If tiered storage is enabled this is the
 # amount of data to retain total. Otherwise, this can be used as a large volume
@@ -810,7 +814,9 @@ def _test_many_partitions(self,
                                 replication_factor,
                                 mib_per_partition,
                                 topic_partitions_per_shard,
-                                tiered_storage_enabled=tiered_storage_enabled)
+                                tiered_storage_enabled=tiered_storage_enabled,
+                                partition_memory_reserve_percentage=
+                                DEFAULT_PARTITIONS_MEMORY_ALLOCATION_PERCENT)
 
         # Run with one huge topic: it is more stressful for redpanda when clients
         # request the metadata for many partitions at once, and the simplest way
@@ -847,6 +853,8 @@ def _test_many_partitions(self,
             topic_partitions_per_shard,
             'topic_memory_per_partition':
             mib_per_partition * 1024 * 1024,
+            'topic_partitions_memory_allocation_percent':
+            DEFAULT_PARTITIONS_MEMORY_ALLOCATION_PERCENT,
         })
 
         self.redpanda.start()

tests/rptest/utils/scale_parameters.py

@@ -25,9 +25,11 @@ def __init__(self,
                  replication_factor,
                  mib_per_partition,
                  topic_partitions_per_shard,
-                 tiered_storage_enabled=False):
+                 tiered_storage_enabled=False,
+                 partition_memory_reserve_percentage=10):
         self.redpanda = redpanda
         self.tiered_storage_enabled = tiered_storage_enabled
+        self.partition_memory_reserve_percentage = partition_memory_reserve_percentage
 
         node_count = len(self.redpanda.nodes)
 
@@ -171,23 +173,23 @@ def __init__(self,
         # Not all internal partitions have rf=replication_factor so this
         # over-allocates but making it more accurate would be complicated.
         per_node_slack = internal_partition_slack * replication_factor / node_count
-        partition_mem_total_per_node = mib_per_partition * (
-            partition_replicas_per_node + per_node_slack)
+        memory_setting = mib_per_partition * (
+            partition_replicas_per_node +
+            per_node_slack) * (self.partition_memory_reserve_percentage / 100.)
 
         resource_settings_args = {}
         if not self.redpanda.dedicated_nodes:
             # In docker, assume we're on a laptop drive and not doing
             # real testing, so disable fsync to make test run faster.
             resource_settings_args['bypass_fsync'] = True
 
-            partition_mem_total_per_node = max(partition_mem_total_per_node,
-                                               500)
+            memory_setting = max(memory_setting, 500)
         else:
             # On dedicated nodes we will use an explicit reactor stall threshold
             # as a success condition.
             resource_settings_args['reactor_stall_threshold'] = 100
 
-        resource_settings_args['memory_mb'] = int(partition_mem_total_per_node)
+        resource_settings_args['memory_mb'] = int(memory_setting)
 
         self.redpanda.set_resource_settings(
             ResourceSettings(**resource_settings_args))
@@ -198,7 +200,7 @@ def __init__(self,
 
         # Should not happen on the expected EC2 instance types where
         # the cores-RAM ratio is sufficient to meet our shards-per-core
-        if effective_node_memory < partition_mem_total_per_node:
+        if effective_node_memory < memory_setting:
             raise RuntimeError(
                 f"Node memory is too small ({node_memory}MB - {reserved_memory}MB)"
             )