[Placement Group]Add soft pack strategy (#10099)

python/ray/_raylet.pyx

@@ -69,6 +69,7 @@ from ray.includes.common cimport (
     WORKER_TYPE_IO_WORKER,
     PLACEMENT_STRATEGY_PACK,
     PLACEMENT_STRATEGY_SPREAD,
+    PLACEMENT_STRATEGY_STRICT_PACK,
 )
 from ray.includes.unique_ids cimport (
     CActorID,
@@ -1061,9 +1062,11 @@ cdef class CoreWorker:
 
         if strategy == b"PACK":
             c_strategy = PLACEMENT_STRATEGY_PACK
+        elif strategy == b"SPREAD":
+            c_strategy = PLACEMENT_STRATEGY_SPREAD
         else:
-            if strategy == b"SPREAD":
-                c_strategy = PLACEMENT_STRATEGY_SPREAD
+            if strategy == b"STRICT_PACK":
+                c_strategy = PLACEMENT_STRATEGY_STRICT_PACK
             else:
                 raise TypeError(strategy)
 

python/ray/experimental/placement_group.py

@@ -13,11 +13,10 @@ def placement_group(bundles: List[Dict[str, float]],
     Args:
         bundles: A list of bundles which represent the resources needed.
         strategy: The strategy to create the placement group.
-            There are two build-in strategies for the time begin.
-            PACK: Packs Bundles close together inside processes or nodes as
-            tight as possible.
-            SPREAD: Places Bundles across distinct nodes or processes as even
-            as possible.
+            PACK: Packs Bundles into as few nodes as possible.
+            SPREAD: Places Bundles across distinct nodes as even as possible.
+            STRICT_PACK: Packs Bundles into one node.
+            The group is not allowed to span multiple nodes.
         name: The name of the placement group.
     """
     worker = ray.worker.global_worker

python/ray/includes/common.pxd

@@ -174,6 +174,8 @@ cdef extern from "src/ray/protobuf/common.pb.h" nogil:
         "ray::PlacementStrategy::PACK"
     cdef CPlacementStrategy PLACEMENT_STRATEGY_SPREAD \
         "ray::PlacementStrategy::SPREAD"
+    cdef CPlacementStrategy PLACEMENT_STRATEGY_STRICT_PACK \
+        "ray::PlacementStrategy::STRICT_PACK"
 
 cdef extern from "ray/common/task/scheduling_resources.h" nogil:
     cdef cppclass ResourceSet "ray::ResourceSet":

python/ray/tests/test_placement_group.py

@@ -57,6 +57,51 @@ def test_placement_group_pack(ray_start_cluster):
     assert node_of_actor_1 == node_of_actor_2
 
 
+def test_placement_group_strict_pack(ray_start_cluster):
+    @ray.remote(num_cpus=2)
+    class Actor(object):
+        def __init__(self):
+            self.n = 0
+
+        def value(self):
+            return self.n
+
+    cluster = ray_start_cluster
+    num_nodes = 2
+    for _ in range(num_nodes):
+        cluster.add_node(num_cpus=4)
+    ray.init(address=cluster.address)
+
+    placement_group_id = ray.experimental.placement_group(
+        name="name", strategy="STRICT_PACK", bundles=[{
+            "CPU": 2
+        }, {
+            "CPU": 2
+        }])
+    actor_1 = Actor.options(
+        placement_group_id=placement_group_id,
+        placement_group_bundle_index=0).remote()
+    actor_2 = Actor.options(
+        placement_group_id=placement_group_id,
+        placement_group_bundle_index=1).remote()
+
+    print(ray.get(actor_1.value.remote()))
+    print(ray.get(actor_2.value.remote()))
+
+    # Get all actors.
+    actor_infos = ray.actors()
+
+    # Make sure all actors in counter_list are collocated in one node.
+    actor_info_1 = actor_infos.get(actor_1._actor_id.hex())
+    actor_info_2 = actor_infos.get(actor_2._actor_id.hex())
+
+    assert actor_info_1 and actor_info_2
+
+    node_of_actor_1 = actor_info_1["Address"]["NodeID"]
+    node_of_actor_2 = actor_info_2["Address"]["NodeID"]
+    assert node_of_actor_1 == node_of_actor_2
+
+
 def test_placement_group_spread(ray_start_cluster):
     @ray.remote(num_cpus=2)
     class Actor(object):