2b.3 observability: repoint lane-stats occ/used at the shared pool when pooling on

When --enable-cp-shared-physical-l2-hicache is on, the lane-stats occ/used_tokens
read 0 (they derive from _cp_counts, which the accounting skips for shared-L2
metadata) -- the per-rank gauge is meaningless. Repoint occ/used/cap at the
shared pool's per-payload-slab fill (target_kv/draft_kv/index_k) via the new
CpSharedL2PageAllocator.occupancy_by_payload(); add occ_by={payload,rank} +
occ_labels so the line is self-describing. The real cp_size (owner round-robin
period for the hot-prefix skew) is now computed independently of the occ-vector
length. Per-rank (flag-off) path unchanged. Read-only; rank-0; next-restart.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

python/sglang/srt/mem_cache/cp_shared_l2_pool.py

@@ -786,6 +786,16 @@ class CpSharedL2PageAllocator:
         total = self._payload_capacity(payload_kind)
         return total - self.free_pages(payload_kind)
 
+    def occupancy_by_payload(self) -> dict[str, tuple[int, int]]:
+        """Per-payload-slab ``(used_pages, capacity_pages)`` in a stable payload
+        order. For the lane-stats observability probe: the shared pool's REAL fill,
+        broken down by payload slab (target_kv/draft_kv/index_k). Derived purely
+        from the replicated free list, so identical on every CP rank."""
+        return {
+            payload: (self.used_pages(payload), self._payload_capacity(payload))
+            for payload in sorted(self._free_by_payload)
+        }
+
     def stats(self) -> dict[str, int]:
         capacity = {
             payload: self._payload_capacity(payload)

python/sglang/srt/mem_cache/hiradix_cache.py

@@ -3253,13 +3253,35 @@ class HiRadixCache(RadixCache):
             return
         self._cp_lane_stats_last_emit = now
 
-        snapshot = self._cp_host_capacity_snapshot()
-        capacity = snapshot.target_capacity
-        used = snapshot.target_used
-        cp_size = len(capacity)
+        # Real cp_size (owner round-robin period for the hot-prefix skew below) --
+        # decoupled from the occ-vector length, which is per-payload when pooling.
+        cp_size = self._cp_hicache_cp_size()
+        controller = getattr(self, "cache_controller", None)
+        allocator = (
+            getattr(controller, "cp_shared_l2_page_allocator", None)
+            if controller is not None
+            else None
+        )
+        if allocator is not None and hasattr(allocator, "occupancy_by_payload"):
+            # l2 pooling ON: report the shared pool's per-payload-slab fill. The
+            # per-rank snapshot (_cp_counts -> target_used) is 0 here because the
+            # accounting skips shared-L2 metadata (_cp_account_*: `not
+            # _is_cp_shared_l2_metadata`), so the per-rank gauge is meaningless --
+            # repoint occ/used/cap at the actual pool.
+            by_payload = allocator.occupancy_by_payload()
+            occ_labels = list(by_payload.keys())
+            used = [by_payload[p][0] for p in occ_labels]
+            capacity = [by_payload[p][1] for p in occ_labels]
+            occ_by = "payload"
+        else:
+            snapshot = self._cp_host_capacity_snapshot()
+            capacity = list(snapshot.target_capacity)
+            used = list(snapshot.target_used)
+            occ_labels = [f"lane{i}" for i in range(len(capacity))]
+            occ_by = "rank"
         occ = [
             (used[i] / capacity[i]) if capacity[i] > 0 else 0.0
-            for i in range(cp_size)
+            for i in range(len(capacity))
         ]
         max_occ = max(occ) if occ else 0.0
         min_occ = min(occ) if occ else 0.0
@@ -3300,10 +3322,7 @@ class HiRadixCache(RadixCache):
         # shared pool tracks its own pages_used/objects_committed/objects_evicted +
         # load_hits/misses in the replicated CpSharedL2PageAllocator stats.
         shared_l2_report = None
-        controller = getattr(self, "cache_controller", None)
-        if controller is not None and getattr(
-            controller, "cp_shared_l2_page_allocator", None
-        ) is not None:
+        if allocator is not None and controller is not None:
             report_fn = getattr(controller, "cp_shared_l2_cache_report", None)
             if report_fn is not None:
                 try:
@@ -3312,10 +3331,13 @@ class HiRadixCache(RadixCache):
                     shared_l2_report = None
 
         logger.info(
-            "[CP_HICACHE_LANE_STATS] occ=%s cap_tokens=%s used_tokens=%s max=%.3f "
+            "[CP_HICACHE_LANE_STATS] occ_by=%s occ=%s occ_labels=%s cap=%s "
+            "used=%s max=%.3f "
             "min=%.3f spread=%.3f imbalance=%s hot_prefix_short=%d hot_prefix_long=%d "
             "skew_token_threshold=%d drops_since_last=%s drops_total=%s shared_l2_pool=%s",
+            occ_by,
             [round(x, 3) for x in occ],
+            occ_labels,
             list(capacity),
             list(used),
             max_occ,