Add comments to variable definitions

Review comments:

- #41727 (comment)
- #41727 (comment)

Signed-off-by: Martin Hickey <martin.hickey@ie.ibm.com>

Author: hickeyma

vllm/v1/kv_offload/cpu/manager.py

@@ -55,6 +55,8 @@ def __init__(
         self._policy: CachePolicy = policy_cls(cache_capacity=num_blocks)
         self.store_threshold: int = store_threshold
         self.max_tracker_size: int = max_tracker_size
+
+        # Number of block references. It is ordered so can evict the LRU entry in O(1).
         self.counts: OrderedDict[OffloadKey, int] | None = (
             OrderedDict() if store_threshold >= 2 else None
         )

vllm/v1/kv_offload/cpu/spec.py

@@ -59,8 +59,15 @@ def get_manager(self) -> OffloadingManager:
             enable_events = (
                 kv_events_config is not None and kv_events_config.enable_kv_cache_events
             )
+
+            # store_threshold: how many times a block must appear in lookup()
+            # before it is eligible for CPU offloading.  Values < 2 disable
+            # filtering (a threshold of 1 equals no filter; 0 is the default).
             store_threshold = int(self.extra_config.get("store_threshold", 0))
+
+            # Maximum entries in the internal tracker's LRU table.
             max_tracker_size = int(self.extra_config.get("max_tracker_size", 64_000))
+
             self._manager = CPUOffloadingManager(
                 num_blocks=self.num_blocks,
                 cache_policy=self.eviction_policy,  # type: ignore[arg-type]