From 2df832dec0e5ba0534be06646f1683bb5c882ab1 Mon Sep 17 00:00:00 2001
From: ThomasX <thomas.x@outlook.com>
Date: Fri, 8 May 2026 01:59:14 +0800
Subject: [PATCH] fix: unblock CP host eviction past stale leaves

---
 python/sglang/srt/mem_cache/hiradix_cache.py  |  5 ++
 .../mem_cache/test_cp_hicache_metadata.py     | 52 +++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/python/sglang/srt/mem_cache/hiradix_cache.py b/python/sglang/srt/mem_cache/hiradix_cache.py
index 0809b49ef..505e0afd3 100644
--- a/python/sglang/srt/mem_cache/hiradix_cache.py
+++ b/python/sglang/srt/mem_cache/hiradix_cache.py
@@ -1102,6 +1102,11 @@ class HiRadixCache(RadixCache):
                 continue
 
             if not self._node_backuped(x):
+                if len(x.children) == 0:
+                    parent = self._remove_host_leaf(x)
+                    if parent.evicted and self._node_backuped(parent):
+                        new_priority = self.eviction_strategy.get_priority(parent)
+                        heapq.heappush(eviction_heap, (new_priority, parent))
                 continue
 
             if x.pin_expiry > 0 and time.monotonic() > x.pin_expiry:
diff --git a/test/registered/unit/mem_cache/test_cp_hicache_metadata.py b/test/registered/unit/mem_cache/test_cp_hicache_metadata.py
index 5aabf1599..4ab7f0827 100644
--- a/test/registered/unit/mem_cache/test_cp_hicache_metadata.py
+++ b/test/registered/unit/mem_cache/test_cp_hicache_metadata.py
@@ -379,6 +379,58 @@ class TestHiRadixCacheCPSplitEvict(CustomTestCase):
         self.assertEqual(node.host_len, 0)
         self.assertIsNone(node.cp_hicache)
 
+    def test_cp_host_eviction_unlinks_stale_leaf_to_free_parent_slots(self):
+        cache = HiRadixCache.__new__(HiRadixCache)
+        cache._uses_cp_hicache = True
+        cache.root_node = TreeNode()
+        cache.root_node.key = RadixKey([])
+        cache.evictable_host_leaves = set()
+        cache.get_child_key_fn = lambda key: key.token_ids[0]
+        cache.eviction_strategy = type(
+            "Strategy", (), {"get_priority": lambda self, node: 0}
+        )()
+        cache._clear_pin = lambda node: None
+        cache._record_remove_event = lambda node: None
+        freed = []
+        cache.cache_controller = type(
+            "Controller",
+            (),
+            {
+                "evict_host": lambda self, indices: freed.append(indices.clone())
+                or len(indices)
+            },
+        )()
+
+        parent = TreeNode()
+        parent.parent = cache.root_node
+        parent.key = RadixKey([1])
+        parent.value = None
+        parent.host_len = 4
+        parent.cp_hicache = CpHiCacheNodeMetadata(
+            logical_len=4,
+            owned_positions=torch.tensor([2], dtype=torch.int64),
+            host_indices=torch.tensor([80], dtype=torch.int64),
+        )
+        cache.root_node.children[1] = parent
+
+        stale_child = TreeNode()
+        stale_child.parent = parent
+        stale_child.key = RadixKey([2])
+        stale_child.value = None
+        stale_child.host_len = 0
+        stale_child.cp_hicache = None
+        parent.children[2] = stale_child
+        cache.evictable_host_leaves.add(stale_child)
+
+        physical_freed = cache._evict_host_for_physical_slots(1)
+
+        self.assertEqual(physical_freed, 1)
+        self.assertEqual(freed[0].tolist(), [80])
+        self.assertNotIn(2, parent.children)
+        self.assertEqual(parent.host_len, 0)
+        self.assertIsNone(parent.cp_hicache)
+        self.assertNotIn(1, cache.root_node.children)
+
 
 if __name__ == "__main__":
     unittest.main()