[unified-memory] Stop eviction when shared allocation capacity is sufficient (#33091)

Co-authored-by: seokwoosong <seokwoosong@users.noreply.github.com>

benchmark/unified_memory/bench_peer_aware_eviction.py

@@ -0,0 +1,246 @@
+"""Reproduce and measure peer-aware eviction in the unified memory pool.
+
+The workload deliberately fills the shared FULL/Mamba pool with many small,
+reusable prefixes.  It then submits one long pressure request and probes every
+prefix again.  Keeping more probe prefixes cached demonstrates that allocator
+capacity gained from a peer component stopped radix eviction early.
+
+Example:
+
+    python benchmark/unified_memory/bench_peer_aware_eviction.py \
+        --label proposed --output /tmp/proposed.json
+
+Concurrent fan-out from a prefix retained only by the proposed path:
+
+    python benchmark/unified_memory/bench_peer_aware_eviction.py \
+        --model-path Qwen/Qwen3.5-4B \
+        --probe-output-len 32 --probe-concurrency 6 \
+        --burst-target-index 14 --burst-requests 30 \
+        --label proposed-concurrent --output /tmp/proposed-concurrent.json
+"""
+
+from __future__ import annotations
+
+import argparse
+import json
+import statistics
+import time
+from concurrent.futures import ThreadPoolExecutor
+from pathlib import Path
+from typing import Any
+
+import requests
+from transformers import AutoTokenizer
+
+
+def percentile(values: list[float], fraction: float) -> float:
+    values = sorted(values)
+    if not values:
+        return 0.0
+    return values[round((len(values) - 1) * fraction)]
+
+
+def generate(base_url: str, text: str, max_new_tokens: int) -> dict:
+    start = time.perf_counter()
+    response = requests.post(
+        f"{base_url}/generate",
+        json={
+            "text": text,
+            "sampling_params": {
+                "max_new_tokens": max_new_tokens,
+                "temperature": 0,
+                "ignore_eos": True,
+            },
+        },
+        timeout=600,
+    )
+    elapsed = time.perf_counter() - start
+    response.raise_for_status()
+    body = response.json()
+    meta = body["meta_info"]
+    prefill_finished_time = meta.get("prefill_finished_time")
+    forward_entry_time = meta.get("forward_entry_time")
+    return {
+        "prompt_tokens": meta["prompt_tokens"],
+        "cached_tokens": meta["cached_tokens"],
+        "e2e_latency_s": meta["e2e_latency"],
+        "client_latency_s": elapsed,
+        "prefill_latency_s": (
+            prefill_finished_time - forward_entry_time
+            if prefill_finished_time is not None and forward_entry_time is not None
+            else None
+        ),
+        "completion_tokens": meta["completion_tokens"],
+        "num_retractions": meta["num_retractions"],
+        "output_ids": body["output_ids"],
+    }
+
+
+def text_with_target_tokens(tokenizer, seed: str, target: int) -> str:
+    """Create deterministic text whose tokenized length is close to ``target``."""
+    repeated = (seed + " ") * target
+    token_ids = tokenizer.encode(repeated, add_special_tokens=False)[:target]
+    return tokenizer.decode(token_ids, skip_special_tokens=True)
+
+
+def summarize_probe(probes: list[dict], batch_wall_latency_s: float) -> dict[str, Any]:
+    cached = [item["cached_tokens"] for item in probes]
+    e2e = [item["e2e_latency_s"] for item in probes]
+    client = [item["client_latency_s"] for item in probes]
+    prefill = [
+        item["prefill_latency_s"]
+        for item in probes
+        if item["prefill_latency_s"] is not None
+    ]
+    completion_tokens = sum(item["completion_tokens"] for item in probes)
+    return {
+        "cached_prefixes": sum(value > 0 for value in cached),
+        "cache_survival_rate": sum(value > 0 for value in cached) / len(cached),
+        "total_cached_tokens": sum(cached),
+        "mean_cached_tokens": statistics.mean(cached),
+        "cached_tokens": cached,
+        "mean_e2e_latency_s": statistics.mean(e2e),
+        "p95_e2e_latency_s": percentile(e2e, 0.95),
+        "mean_client_latency_s": statistics.mean(client),
+        "p95_client_latency_s": percentile(client, 0.95),
+        "mean_prefill_latency_s": statistics.mean(prefill) if prefill else None,
+        "p95_prefill_latency_s": percentile(prefill, 0.95) if prefill else None,
+        "batch_wall_latency_s": batch_wall_latency_s,
+        "request_throughput_rps": len(probes) / batch_wall_latency_s,
+        "output_throughput_tps": completion_tokens / batch_wall_latency_s,
+        "completion_tokens": completion_tokens,
+        "total_retractions": sum(item["num_retractions"] for item in probes),
+    }
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--base-url", default="http://127.0.0.1:30000")
+    parser.add_argument("--model-path", default="Qwen/Qwen3.5-0.8B")
+    parser.add_argument("--label", required=True)
+    parser.add_argument("--output", type=Path, required=True)
+    parser.add_argument("--warm-prefixes", type=int, default=28)
+    parser.add_argument("--prefix-len", type=int, default=400)
+    parser.add_argument("--pressure-len", type=int, default=7000)
+    parser.add_argument("--output-len", type=int, default=1)
+    parser.add_argument("--probe-output-len", type=int)
+    parser.add_argument("--probe-concurrency", type=int, default=1)
+    parser.add_argument("--burst-target-index", type=int)
+    parser.add_argument("--burst-requests", type=int, default=30)
+    args = parser.parse_args()
+    if args.probe_concurrency < 1:
+        parser.error("--probe-concurrency must be at least 1")
+    if args.burst_requests < 1:
+        parser.error("--burst-requests must be at least 1")
+    if args.burst_target_index is not None and not (
+        0 <= args.burst_target_index < args.warm_prefixes
+    ):
+        parser.error("--burst-target-index must select a warm prefix")
+    probe_output_len = args.probe_output_len or args.output_len
+    tokenizer = AutoTokenizer.from_pretrained(args.model_path)
+
+    prompt_pairs = []
+    prompt_bases = []
+    for index in range(args.warm_prefixes):
+        base = text_with_target_tokens(
+            tokenizer,
+            f"stable reusable unified cache prefix group {index}",
+            args.prefix_len - 16,
+        )
+        prompt_bases.append(base)
+        prompt_pairs.append(
+            (
+                base + f" warm suffix for group {index}",
+                base + f" replay suffix for group {index}",
+            )
+        )
+    pressure_text = text_with_target_tokens(
+        tokenizer, "distinct long allocation pressure payload", args.pressure_len
+    )
+
+    requests.post(f"{args.base_url}/flush_cache", timeout=60).raise_for_status()
+
+    # Exclude server startup and first-request kernel initialization.
+    generate(args.base_url, "server kernel warmup " * 32, args.output_len)
+    requests.post(f"{args.base_url}/flush_cache", timeout=60).raise_for_status()
+
+    warm = []
+    for warm_text, _ in prompt_pairs:
+        warm.append(
+            generate(
+                args.base_url,
+                warm_text,
+                args.output_len,
+            )
+        )
+
+    # A distinct long request forces the FULL side toward the Mamba frontier.
+    pressure = generate(
+        args.base_url,
+        pressure_text,
+        args.output_len,
+    )
+
+    if args.burst_target_index is None:
+        probe_indices = list(reversed(range(len(prompt_pairs))))
+        probe_texts = [prompt_pairs[index][1] for index in probe_indices]
+    else:
+        probe_indices = [args.burst_target_index] * args.burst_requests
+        target_base = prompt_bases[args.burst_target_index]
+        probe_texts = [
+            target_base + f" concurrent burst replay suffix request {ordinal}"
+            for ordinal in range(args.burst_requests)
+        ]
+
+    def run_probe(replay_text: str) -> dict:
+        return generate(
+            args.base_url,
+            replay_text,
+            probe_output_len,
+        )
+
+    probe_start = time.perf_counter()
+    if args.probe_concurrency == 1:
+        probes = [run_probe(replay_text) for replay_text in probe_texts]
+    else:
+        with ThreadPoolExecutor(max_workers=args.probe_concurrency) as executor:
+            probes = list(executor.map(run_probe, probe_texts))
+    probe_wall_latency_s = time.perf_counter() - probe_start
+
+    result = {
+        "label": args.label,
+        "config": {
+            "warm_prefixes": args.warm_prefixes,
+            "prefix_len": args.prefix_len,
+            "pressure_len": args.pressure_len,
+            "output_len": args.output_len,
+            "probe_output_len": probe_output_len,
+            "probe_concurrency": args.probe_concurrency,
+            "burst_target_index": args.burst_target_index,
+            "burst_requests": (
+                args.burst_requests if args.burst_target_index is not None else None
+            ),
+            "actual_warm_prompt_tokens": [item["prompt_tokens"] for item in warm],
+        },
+        "warm": {
+            "total_cached_tokens": sum(item["cached_tokens"] for item in warm),
+            "total_retractions": sum(item["num_retractions"] for item in warm),
+        },
+        "warm_requests": warm,
+        "pressure": pressure,
+        "probe": summarize_probe(probes, probe_wall_latency_s),
+        "probe_requests": probes,
+        "probe_indices": probe_indices,
+        "output_ids": {
+            "warm": [item["output_ids"] for item in warm],
+            "pressure": pressure["output_ids"],
+            "probe": [item["output_ids"] for item in probes],
+        },
+    }
+    args.output.parent.mkdir(parents=True, exist_ok=True)
+    args.output.write_text(json.dumps(result, indent=2) + "\n")
+    print(json.dumps(result["probe"], indent=2))
+
+
+if __name__ == "__main__":
+    main()

python/sglang/srt/disaggregation/decode.py

@@ -427,7 +427,9 @@ class DecodePreallocQueue(DecodeHiCachePreallocMixin):
         required = ceil_align(swa_tail_len, page_size)
         available = self.token_to_kv_pool_allocator.swa_available_size()
         if available < required:
-            self.tree_cache.evict(EvictParams(swa_num_tokens=required - available))
+            self.tree_cache.evict_for_alloc(
+                EvictParams(swa_num_tokens=required - available)
+            )
             available = self.token_to_kv_pool_allocator.swa_available_size()
 
         if available < required:
@@ -1789,7 +1791,9 @@ class DecodePreallocQueue(DecodeHiCachePreallocMixin):
             and self._radix_full_available() < required_alloc_tokens
         ):
             num_to_evict = required_alloc_tokens - self._radix_full_available()
-            result = self.tree_cache.evict(EvictParams(num_tokens=num_to_evict))
+            result = self.tree_cache.evict_for_alloc(
+                EvictParams(num_tokens=num_to_evict)
+            )
             if self._radix_full_available() < required_alloc_tokens:
                 logger.warning(
                     f"Eviction insufficient: needed {required_alloc_tokens} tokens, "

python/sglang/srt/hardware_backend/mlx/kv_cache/auxiliary_state.py

@@ -10,7 +10,7 @@ storing model-agnostic native cache snapshots.
 from __future__ import annotations
 
 from dataclasses import dataclass
-from typing import Any, Iterable, Optional
+from typing import Any, Iterable, Iterator, Optional
 
 import mlx.core as mx
 import torch
@@ -95,6 +95,7 @@ class MlxAuxiliaryStatePool:
         self.mamba_cache = None
         self.mem_usage = 0
         self._snapshots: dict[int, dict[int, _CacheSnapshot]] = {}
+        self._alloc_iter: Optional[Iterator[torch.Tensor]] = None
         self.clear()
 
     def _tensor(self, indices: Any) -> torch.Tensor:
@@ -108,7 +109,31 @@ class MlxAuxiliaryStatePool:
     def available_size(self) -> int:
         return int(self.free_slots.numel())
 
+    def schedulable_available_size(self) -> int:
+        return self.available_size()
+
+    def alloc_group_begin(self, num_reqs: int) -> None:
+        self._alloc_iter = None
+        if num_reqs > 0:
+            slots = self._do_alloc(num_reqs)
+            if slots is not None:
+                self._alloc_iter = iter(slots.split(1))
+
+    def alloc_group_end(self) -> None:
+        if self._alloc_iter is not None:
+            remaining = list(self._alloc_iter)
+            if remaining:
+                self.free(torch.cat(remaining))
+        self._alloc_iter = None
+
     def alloc(self, need_size: int) -> Optional[torch.Tensor]:
+        if self._alloc_iter is not None and need_size == 1:
+            slot = next(self._alloc_iter, None)
+            if slot is not None:
+                return slot
+        return self._do_alloc(need_size)
+
+    def _do_alloc(self, need_size: int) -> Optional[torch.Tensor]:
         if need_size > self.available_size():
             return None
         slots = self.free_slots[:need_size].clone()
@@ -128,6 +153,7 @@ class MlxAuxiliaryStatePool:
         self.free_slots = torch.cat([self.free_slots, indices])
 
     def clear(self) -> None:
+        self._alloc_iter = None
         self.free_slots = torch.arange(
             1, self.size + 1, dtype=torch.int64, device=self.device
         )
@@ -227,6 +253,7 @@ class MlxAuxiliaryStateReqToTokenPool(ReqToTokenPool):
             size=auxiliary_state_size,
             device=device,
         )
+        self.mamba_allocator = self.mamba_pool
         # The unified radix base MAMBA component still reads ``mamba_pool``.
         # Keep the MLX-owned name beside it so local code can avoid model-
         # specific terminology.
@@ -352,7 +379,7 @@ class MlxAuxiliaryStateComponent(MambaComponent):
                 source_value
             )
             if forked_value is None:
-                self.cache.evict(EvictParams(num_tokens=0, mamba_num=1))
+                self.cache.evict_for_alloc(EvictParams(num_tokens=0, mamba_num=1))
                 forked_value = (
                     self.cache.req_to_token_pool.auxiliary_state_pool.fork_from(
                         source_value

python/sglang/srt/mem_cache/allocation.py

@@ -257,7 +257,9 @@ def alloc_req_slots(
         if mamba_available_size < mamba_state_needed:
             if tree_cache is not None and tree_cache.supports_mamba():
                 mamba_num = max(0, mamba_state_needed - mamba_available_size)
-                tree_cache.evict(EvictParams(num_tokens=0, mamba_num=mamba_num))
+                tree_cache.evict_for_alloc(
+                    EvictParams(num_tokens=0, mamba_num=mamba_num)
+                )
     req_pool_indices = req_to_token_pool.alloc(reqs)
     if req_pool_indices is None:
         raise RuntimeError(

python/sglang/srt/mem_cache/base_prefix_cache.py

@@ -324,6 +324,16 @@ class BasePrefixCache(ABC, PrefixCacheTrait):
     def evict(self, params: EvictParams) -> EvictResult:
         pass
 
+    def evict_for_alloc(self, params: EvictParams) -> EvictResult:
+        """Evict cache entries to cover allocator shortfalls.
+
+        The default implementation preserves the component-count semantics of
+        :meth:`evict`. Multi-component caches backed by shared memory can
+        override this entry point to stop once collateral frees make the
+        requested allocation feasible.
+        """
+        return self.evict(params)
+
     @abstractmethod
     def inc_lock_ref(self, node: Any) -> IncLockRefResult:
         pass

python/sglang/srt/mem_cache/buffer_mode/pipeline.py

@@ -832,8 +832,12 @@ class BufferModePipeline:
             avail = cache.token_to_kv_pool_allocator.available_size()
         if avail < f.num_tokens:
             needed = f.num_tokens - avail
-            evicted = cache.evict(EvictParams(num_tokens=needed))
+            cache.evict_for_alloc(EvictParams(num_tokens=needed))
-            if evicted.num_tokens_evicted < needed:
+            if cache.supports_swa():
+                avail = cache.token_to_kv_pool_allocator.full_available_size()
+            else:
+                avail = cache.token_to_kv_pool_allocator.available_size()
+            if avail < f.num_tokens:
                 # Genuinely no room (locked pages): recompute.
                 return _drop()
 

python/sglang/srt/mem_cache/common.py

@@ -130,14 +130,16 @@ def evict_from_tree_cache(tree_cache: BasePrefixCache | None, num_tokens: int):
         if full_available_size < num_tokens or swa_available_size < num_tokens:
             full_num_tokens = max(0, num_tokens - full_available_size)
             swa_num_tokens = max(0, num_tokens - swa_available_size)
-            tree_cache.evict(
+            tree_cache.evict_for_alloc(
                 EvictParams(num_tokens=full_num_tokens, swa_num_tokens=swa_num_tokens)
             )
     else:
         # Standard allocator: evict only the shortfall (mirrors the SWA arm)
         available_size = allocator.available_size()
         if available_size < num_tokens:
-            tree_cache.evict(EvictParams(num_tokens=num_tokens - available_size))
+            tree_cache.evict_for_alloc(
+                EvictParams(num_tokens=num_tokens - available_size)
+            )
 
 
 def retraction_backup(

python/sglang/srt/mem_cache/hybrid_cache/hybrid_pool_assembler.py

@@ -48,6 +48,26 @@ def _get_allocator_type(server_args: ServerArgs) -> str:
     return get_allocator_type(server_args)
 
 
+def _evict_swa_for_device_alloc(cache: UnifiedRadixCache, required_size: int) -> None:
+    from sglang.srt.mem_cache.base_prefix_cache import EvictParams
+
+    available_size = cache.token_to_kv_pool_allocator.swa_available_size()
+    shortfall = max(0, required_size - available_size)
+    if shortfall > 0:
+        cache.evict_for_alloc(EvictParams(swa_num_tokens=shortfall))
+
+
+def _evict_mamba_for_device_alloc(cache: UnifiedRadixCache, required_size: int) -> None:
+    from sglang.srt.mem_cache.base_prefix_cache import EvictParams
+
+    available_size = (
+        cache.req_to_token_pool.mamba_allocator.schedulable_available_size()
+    )
+    shortfall = max(0, required_size - available_size)
+    if shortfall > 0:
+        cache.evict_for_alloc(EvictParams(mamba_num=shortfall))
+
+
 def _make_layer_mapper(
     layer_mapping: dict[int, int],
     transfer_layer_num: int,
@@ -1210,8 +1230,6 @@ class _DeepSeekV4Strategy(StackStrategy):
         model_name=None,
         enable_storage_metrics=False,
     ):
-        from sglang.srt.mem_cache.base_prefix_cache import EvictParams
-
         host_pool_group, cache_controller = build_deepseek_v4_hicache_stack(
             params=params,
             server_args=server_args,
@@ -1219,7 +1237,7 @@ class _DeepSeekV4Strategy(StackStrategy):
             load_cache_event=load_cache_event,
             storage_backend=storage_backend,
             host_swa_evict_fn=lambda n: cache.evict_host(n, ComponentType.SWA),
-            device_swa_evict_fn=lambda n: cache.evict(EvictParams(swa_num_tokens=n)),
+            device_swa_evict_fn=lambda n: _evict_swa_for_device_alloc(cache, n),
             prefetch_threshold=prefetch_threshold,
             model_name=model_name,
             storage_backend_extra_config=storage_backend_extra_config,
@@ -1286,8 +1304,6 @@ class _MambaStrategy(StackStrategy):
         model_name=None,
         enable_storage_metrics=False,
     ):
-        from sglang.srt.mem_cache.base_prefix_cache import EvictParams
-
         full_layer_mapping = dict(kvcache.full_attention_layer_id_mapping)
         mamba_layer_mapping = dict(params.req_to_token_pool.mamba_map)
         host_pool_group, cache_controller = build_hybrid_mamba_stack(
@@ -1301,7 +1317,7 @@ class _MambaStrategy(StackStrategy):
             storage_backend=storage_backend,
             use_mla=kvcache.use_mla,
             host_mamba_evict_fn=lambda n: cache.evict_host(n, ComponentType.MAMBA),
-            device_mamba_evict_fn=lambda n: cache.evict(EvictParams(mamba_num=n)),
+            device_mamba_evict_fn=lambda n: _evict_mamba_for_device_alloc(cache, n),
             prefetch_threshold=prefetch_threshold,
             model_name=model_name,
             storage_backend_extra_config=storage_backend_extra_config,
@@ -1355,8 +1371,6 @@ class _SwaStrategy(StackStrategy):
         model_name=None,
         enable_storage_metrics=False,
     ):
-        from sglang.srt.mem_cache.base_prefix_cache import EvictParams
-
         full_layer_mapping, swa_layer_mapping = _swa_layer_mappings(kvcache)
         host_pool_group, cache_controller = build_hybrid_swa_stack(
             params=params,
@@ -1369,7 +1383,7 @@ class _SwaStrategy(StackStrategy):
             storage_backend=storage_backend,
             use_mla=False,
             host_swa_evict_fn=lambda n: cache.evict_host(n, ComponentType.SWA),
-            device_swa_evict_fn=lambda n: cache.evict(EvictParams(swa_num_tokens=n)),
+            device_swa_evict_fn=lambda n: _evict_swa_for_device_alloc(cache, n),
             prefetch_threshold=prefetch_threshold,
             model_name=model_name,
             storage_backend_extra_config=storage_backend_extra_config,
@@ -1417,8 +1431,6 @@ class _MambaSwaStrategy(StackStrategy):
         model_name=None,
         enable_storage_metrics=False,
     ):
-        from sglang.srt.mem_cache.base_prefix_cache import EvictParams
-
         full_layer_mapping, swa_layer_mapping = _swa_layer_mappings(kvcache)
         mamba_layer_mapping = dict(params.req_to_token_pool.mamba_map)
         host_pool_group, cache_controller = build_hybrid_mamba_swa_stack(
@@ -1438,9 +1450,9 @@ class _MambaSwaStrategy(StackStrategy):
             pp_group=params.pp_cache_group,
             storage_backend=storage_backend,
             host_swa_evict_fn=lambda n: cache.evict_host(n, ComponentType.SWA),
-            device_swa_evict_fn=lambda n: cache.evict(EvictParams(swa_num_tokens=n)),
+            device_swa_evict_fn=lambda n: _evict_swa_for_device_alloc(cache, n),
             host_mamba_evict_fn=lambda n: cache.evict_host(n, ComponentType.MAMBA),
-            device_mamba_evict_fn=lambda n: cache.evict(EvictParams(mamba_num=n)),
+            device_mamba_evict_fn=lambda n: _evict_mamba_for_device_alloc(cache, n),
             prefetch_threshold=prefetch_threshold,
             model_name=model_name,
             storage_backend_extra_config=storage_backend_extra_config,

python/sglang/srt/mem_cache/pool_host/group.py

@@ -16,6 +16,8 @@ class PoolEntry:
     device_pool: Any
     layer_mapper: Callable[[int], int | None]
     is_primary_index_anchor: bool = False
+    # Reclaim callbacks receive the absolute allocation size n. The host
+    # callback evicts n slots; the device callback makes alloc(n) feasible.
     host_evict_fn: Callable[[int], Any] | None = None
     device_evict_fn: Callable[[int], Any] | None = None
     device_alloc_fn: Callable[[int], Any] | None = None

python/sglang/srt/mem_cache/unified_cache/components/mamba_component.py

@@ -203,7 +203,7 @@ class MambaComponent(TreeComponent):
                 # stops at this request's window boundary instead of walking to
                 # root and over-decrementing locks held by other requests.
                 lock_result = self.cache.inc_lock_ref(result.best_match_node)
-                self.cache.evict(EvictParams(num_tokens=0, mamba_num=1))
+                self.cache.evict_for_alloc(EvictParams(num_tokens=0, mamba_num=1))
                 dst_index = self.cache.req_to_token_pool.mamba_allocator.alloc(1)
                 self.cache.dec_lock_ref(
                     result.best_match_node, lock_result.to_dec_params()
@@ -374,10 +374,14 @@ class MambaComponent(TreeComponent):
         device_frees: dict[ComponentType, list[torch.Tensor]],
         host_frees: dict[ComponentType, list[torch.Tensor]],
     ) -> Optional[NodeId]:
-        """Return the next device-leaf node for the driver to evict, or None.
+        """Advance one device-eviction step and return a leaf, if selected.
-        Internal nodes are tombstoned inline (no IO). If the previous node's
+
-        eviction removed the cursor, the walk resumes from the partition
+        An internal tombstone is one complete step so the caller can apply its
-        sentinel with session refs on, else it restarts at the LRU tail."""
+        pending frees and recheck allocator capacity before the next mutation.
+        If the previous node's eviction removed the cursor, the walk resumes
+        from the partition sentinel with session refs on, else it restarts at
+        the LRU tail.
+        """
         ct = self.component_type
         lru = self.tree_core.lru_lists[ct]
         enabled = self.tree_core.enable_session_radix_cache
@@ -387,34 +391,36 @@ class MambaComponent(TreeComponent):
             self._evict_device_cursor = (
                 lru.cursor_next() if enabled else lru.get_lru_no_lock()
             )
-        while (
+        if (
-            tracker[ct] < self._evict_device_request_cnt
+            tracker[ct] >= self._evict_device_request_cnt
-            and self._evict_device_cursor is not None
+            or self._evict_device_cursor is None
-            and lru.in_list(self._evict_device_cursor)
+            or not lru.in_list(self._evict_device_cursor)
         ):
-            x = self._evict_device_cursor
+            return None
-            assert x.component_data[ct].value is not None
+
-            if x in self.tree_core.evictable_device_leaves and (
+        x = self._evict_device_cursor
-                not enabled or self._can_evict_leaf_atomically(x)
+        assert x.component_data[ct].value is not None
-            ):
+        if x in self.tree_core.evictable_device_leaves and (
-                self._evict_device_cursor = (
+            not enabled or self._can_evict_leaf_atomically(x)
-                    lru.cursor_next() if enabled else lru.get_prev_no_lock(x)
+        ):
-                )
+            self._evict_device_cursor = (
-                return x.id
+                lru.cursor_next() if enabled else lru.get_prev_no_lock(x)
-            if not enabled:
-                x_next = lru.get_prev_no_lock(x)
-            self.tree_core._evict_component_and_detach_lru(
-                x,
-                self,
-                target=EvictLayer.DEVICE,
-                tracker=tracker,
-                device_frees=device_frees,
-                host_frees=host_frees,
             )
-            self.tree_core._cascade_evict(
+            return x.id
-                x, self, tracker, device_frees=device_frees, host_frees=host_frees
+        if not enabled:
-            )
+            x_next = lru.get_prev_no_lock(x)
-            self._evict_device_cursor = lru.cursor_next() if enabled else x_next
+        self.tree_core._evict_component_and_detach_lru(
+            x,
+            self,
+            target=EvictLayer.DEVICE,
+            tracker=tracker,
+            device_frees=device_frees,
+            host_frees=host_frees,
+        )
+        self.tree_core._cascade_evict(
+            x, self, tracker, device_frees=device_frees, host_frees=host_frees
+        )
+        self._evict_device_cursor = lru.cursor_next() if enabled else x_next
         return None
 
     def _evict_device_end(self) -> None:
@@ -487,7 +493,7 @@ class MambaComponent(TreeComponent):
         """Allocate one mamba pool slot, evicting if necessary."""
         slot = self.cache.req_to_token_pool.mamba_allocator.alloc(1)
         if slot is None:
-            self.cache.evict(EvictParams(num_tokens=0, mamba_num=1))
+            self.cache.evict_for_alloc(EvictParams(num_tokens=0, mamba_num=1))
             slot = self.cache.req_to_token_pool.mamba_allocator.alloc(1)
             assert slot is not None, "Can not alloc mamba cache"
         return slot
@@ -660,7 +666,7 @@ class MambaComponent(TreeComponent):
             return PrepareLoadBackResult()
         dst = self.cache.req_to_token_pool.mamba_allocator.alloc(1)
         if dst is None:
-            self.cache.evict(EvictParams(num_tokens=0, mamba_num=1))
+            self.cache.evict_for_alloc(EvictParams(num_tokens=0, mamba_num=1))
             dst = self.cache.req_to_token_pool.mamba_allocator.alloc(1)
             assert dst is not None, "Cannot alloc mamba for load_back"
         req.mamba_pool_idx = dst[0]

python/sglang/srt/mem_cache/unified_cache/components/swa_component.py

@@ -535,10 +535,14 @@ class SWAComponent(TreeComponent):
         device_frees: dict[ComponentType, list[torch.Tensor]],
         host_frees: dict[ComponentType, list[torch.Tensor]],
     ) -> Optional[NodeId]:
-        """Return the next device-leaf node for the driver to evict, or None.
+        """Advance one device-eviction step and return a leaf, if selected.
-        Internal nodes are tombstoned inline (no IO). If the previous node's
+
-        eviction removed the cursor, the walk resumes from the partition
+        An internal tombstone is one complete step so the caller can apply its
-        sentinel with session refs on, else it restarts at the LRU tail."""
+        pending frees and recheck allocator capacity before the next mutation.
+        If the previous node's eviction removed the cursor, the walk resumes
+        from the partition sentinel with session refs on, else it restarts at
+        the LRU tail.
+        """
         ct = self.component_type
         lru = self.tree_core.lru_lists[ct]
         enabled = self.tree_core.enable_session_radix_cache
@@ -548,34 +552,36 @@ class SWAComponent(TreeComponent):
             self._evict_device_cursor = (
                 lru.cursor_next() if enabled else lru.get_lru_no_lock()
             )
-        while (
+        if (
-            tracker[ct] < self._evict_device_request_cnt
+            tracker[ct] >= self._evict_device_request_cnt
-            and self._evict_device_cursor is not None
+            or self._evict_device_cursor is None
-            and lru.in_list(self._evict_device_cursor)
+            or not lru.in_list(self._evict_device_cursor)
         ):
-            x = self._evict_device_cursor
+            return None
-            assert x.component_data[ct].value is not None
+
-            if x in self.tree_core.evictable_device_leaves and (
+        x = self._evict_device_cursor
-                not enabled or self._can_evict_leaf_atomically(x)
+        assert x.component_data[ct].value is not None
-            ):
+        if x in self.tree_core.evictable_device_leaves and (
-                self._evict_device_cursor = (
+            not enabled or self._can_evict_leaf_atomically(x)
-                    lru.cursor_next() if enabled else lru.get_prev_no_lock(x)
+        ):
-                )
+            self._evict_device_cursor = (
-                return x.id
+                lru.cursor_next() if enabled else lru.get_prev_no_lock(x)
-            if not enabled:
-                x_next = lru.get_prev_no_lock(x)
-            self.tree_core._evict_component_and_detach_lru(
-                x,
-                self,
-                target=EvictLayer.DEVICE,
-                tracker=tracker,
-                device_frees=device_frees,
-                host_frees=host_frees,
             )
-            self.tree_core._cascade_evict(
+            return x.id
-                x, self, tracker, device_frees=device_frees, host_frees=host_frees
+        if not enabled:
-            )
+            x_next = lru.get_prev_no_lock(x)
-            self._evict_device_cursor = lru.cursor_next() if enabled else x_next
+        self.tree_core._evict_component_and_detach_lru(
+            x,
+            self,
+            target=EvictLayer.DEVICE,
+            tracker=tracker,
+            device_frees=device_frees,
+            host_frees=host_frees,
+        )
+        self.tree_core._cascade_evict(
+            x, self, tracker, device_frees=device_frees, host_frees=host_frees
+        )
+        self._evict_device_cursor = lru.cursor_next() if enabled else x_next
         return None
 
     def _evict_device_end(self) -> None:

python/sglang/srt/mem_cache/unified_cache/components/tree_component.py

@@ -507,8 +507,11 @@ class TreeComponent(ABC):
         device_frees: dict[ComponentType, list[torch.Tensor]],
         host_frees: dict[ComponentType, list[torch.Tensor]],
     ) -> Optional[NodeId]:
-        """Return the next device-leaf node for the driver to evict, or None.
+        """Advance one eviction step and return a device leaf, if selected.
-        Internal nodes are tombstoned inline (no IO)."""
+
+        Implementations must return after one allocator-relevant internal
+        mutation so the caller can drain pending frees before continuing.
+        """
         assert (
             self.is_evict_device_ongoing
         ), f"{self.component_type} device eviction not started"
@@ -534,7 +537,7 @@ class TreeComponent(ABC):
         device_frees: dict[ComponentType, list[torch.Tensor]],
         host_frees: dict[ComponentType, list[torch.Tensor]],
     ) -> Optional[NodeId]:
-        """Advance the walk; return the next device leaf or None."""
+        """Advance the walk by at most one allocator-relevant mutation."""
         ...
 
     @abstractmethod

python/sglang/srt/mem_cache/unified_cache/unified_tree_core.py

@@ -1224,7 +1224,7 @@ class UnifiedTreeCore(UnifiedTreeCoreInterface):
     def evict_device_next_node(
         self, component_type: ComponentType, tracker: dict[ComponentType, int]
     ) -> EvictDeviceNextNodeResult:
-        """Return the next device leaf to evict for a component, or None when done."""
+        """Advance one component eviction step and report whether it progressed."""
         result = EvictDeviceNextNodeResult()
         # The walk reads running totals for its doneness check; the result
         # carries only this step's delta.
@@ -1236,6 +1236,7 @@ class UnifiedTreeCore(UnifiedTreeCoreInterface):
             delta = n - tracker.get(ct, 0)
             if delta:
                 result.tracker[ct] = delta
+        result.made_progress = result.node_id is not None or bool(result.tracker)
         return result
 
     def evict_device_end(self, component_type: ComponentType) -> None:

python/sglang/srt/mem_cache/unified_cache/unified_tree_core_interface.py

@@ -41,7 +41,15 @@ class BaseEvictionResult(msgspec.Struct):
 
 
 class EvictDeviceNextNodeResult(BaseEvictionResult):
+    """One device-walk step.
+
+    ``node_id`` selects a leaf for the Controller to evict. ``made_progress``
+    also covers an internal tombstone that returned no leaf, distinguishing it
+    from true walk exhaustion.
+    """
+
     node_id: Optional[NodeId] = None
+    made_progress: bool = False
 
 
 class EvictDeviceLeafResult(BaseEvictionResult):
@@ -230,8 +238,11 @@ class UnifiedTreeCoreInterface(ABC):
     def evict_device_next_node(
         self, component_type: ComponentType, tracker: dict[ComponentType, int]
     ) -> EvictDeviceNextNodeResult:
-        """The next evictable node (None node_id when the walk is exhausted);
+        """Advance one eviction step.
-        tracker is the caller's running totals, read for the doneness check."""
+
+        A missing ``node_id`` is exhausted only when ``made_progress`` is also
+        false. ``tracker`` is the caller's running totals, read for doneness.
+        """
         ...
 
     @abstractmethod

python/sglang/srt/mem_cache/unified_radix_cache.py

@@ -531,18 +531,68 @@ class UnifiedRadixCache(BasePrefixCache):
             self._apply_cache_actions(self.tree_core.end_insert())
 
     def evict(self, params: EvictParams) -> EvictResult:
+        return self._evict(params)
+
+    def evict_for_alloc(self, params: EvictParams) -> EvictResult:
+        """Evict until the requested component allocations become feasible.
+
+        ``params`` contains allocator shortfalls, not absolute eviction quotas.
+        A component eviction can cascade to its peers; with a shared memory pool,
+        those collateral frees can satisfy the original allocation before the
+        triggering component's requested count is reached.
+        """
         if self.disable:
             return EvictResult()
-        start_time = time.perf_counter()
-        tracker = {ct: 0 for ct in self.tree_components}
 
-        request_by_type = {
+        request_by_type = self._evict_request_by_type(params)
+        available_size_targets = {
+            ct: self._component_available_size(ct) + request_cnt
+            for ct, request_cnt in request_by_type.items()
+            if request_cnt > 0
+        }
+        return self._evict(params, available_size_targets)
+
+    @staticmethod
+    def _evict_request_by_type(params: EvictParams) -> dict[ComponentType, int]:
+        return {
             ComponentType.FULL: params.num_tokens,
             ComponentType.SWA: params.swa_num_tokens,
             ComponentType.MAMBA: params.mamba_num,
             ComponentType.C128: 0,
         }
-        self._evict_components(request_by_type, tracker)
+
+    def _component_available_size(self, component_type: ComponentType) -> int:
+        """Return capacity usable by the component's next allocation.
+
+        Shared allocators expose schedulable capacity, which includes peer holes
+        that an urgent allocator flush can reclaim without further eviction.
+        """
+        if component_type == ComponentType.FULL:
+            if self.supports_swa():
+                return self.token_to_kv_pool_allocator.full_available_size()
+            return self.token_to_kv_pool_allocator.available_size()
+        if component_type == ComponentType.SWA:
+            return self.token_to_kv_pool_allocator.swa_available_size()
+        if component_type == ComponentType.MAMBA:
+            return self.req_to_token_pool.mamba_allocator.schedulable_available_size()
+        raise ValueError(f"Unsupported cache component: {component_type}")
+
+    def _evict(
+        self,
+        params: EvictParams,
+        available_size_targets: Optional[dict[ComponentType, int]] = None,
+    ) -> EvictResult:
+        if self.disable:
+            return EvictResult()
+        start_time = time.perf_counter()
+        tracker = {ct: 0 for ct in self.tree_components}
+
+        request_by_type = self._evict_request_by_type(params)
+        self._evict_components(
+            request_by_type,
+            tracker,
+            available_size_targets=available_size_targets,
+        )
 
         if (
             self.cache_controller is not None
@@ -581,12 +631,12 @@ class UnifiedRadixCache(BasePrefixCache):
 
     def _evict_device_next_node(
         self, component_type: ComponentType, tracker: dict[ComponentType, int]
-    ) -> Optional[NodeId]:
+    ) -> tuple[Optional[NodeId], bool]:
         """Advance the eviction walk one node, consuming its step result."""
         result = self.tree_core.evict_device_next_node(component_type, tracker)
         self._free_values(result.device_frees, result.host_frees)
         self._accumulate_tracker(tracker, result.tracker)
-        return result.node_id
+        return result.node_id, result.made_progress
 
     def _evict_device_leaf(
         self, node_id: NodeId, tracker: dict[ComponentType, int]
@@ -617,20 +667,39 @@ class UnifiedRadixCache(BasePrefixCache):
         self,
         request_by_type: dict[ComponentType, int],
         tracker: dict[ComponentType, int],
+        available_size_targets: Optional[dict[ComponentType, int]] = None,
     ) -> None:
         # Buffer mode: eviction always wins over queued backup intents — a
         # destroyed victim's intent is stale-swept and the content rewrites
         # after its recompute.
+
+        def target_reached(component_type: ComponentType) -> bool:
+            if available_size_targets is None:
+                return False
+            target = available_size_targets.get(component_type)
+            # Do not compact on every eviction step. Shared allocators include
+            # drainable peer holes here and flush the peer once in alloc().
+            return (
+                target is not None
+                and self._component_available_size(component_type) >= target
+            )
+
         for ct in self.tree_components:
             request_cnt = request_by_type[ct]
-            # Skip eviction walk if request is already met
+            # A preceding component may have cascade-evicted this component or,
-            if tracker[ct] >= request_cnt:
+            # on a shared pool, released enough bytes to satisfy its allocation.
+            if tracker[ct] >= request_cnt or target_reached(ct):
                 continue
             self.tree_core.evict_device_start(ct, request_cnt)
             try:
-                while (
+                while not target_reached(ct):
-                    node_id := self._evict_device_next_node(ct, tracker)
+                    node_id, made_progress = self._evict_device_next_node(ct, tracker)
-                ) is not None:
+                    if node_id is None:
+                        if made_progress:
+                            # Internal tombstone frees are now allocator-visible;
+                            # recheck the allocation target before walking again.
+                            continue
+                        break
                     backup_kv = self._evict_device_leaf(node_id, tracker)
                     if backup_kv is not None:
                         # Deferred demote: run the D->H backup, demote only on success.
@@ -1395,14 +1464,11 @@ class UnifiedRadixCache(BasePrefixCache):
             self.dec_host_lock_ref(node_id, host_anchor_params)
             return False
 
-        if self.supports_swa():
+        avail = self._component_available_size(ComponentType.FULL)
-            avail = self.token_to_kv_pool_allocator.full_available_size()
-        else:
-            avail = self.token_to_kv_pool_allocator.available_size()
         if avail < kv_tokens:
             needed = kv_tokens - avail
-            result = self.evict(EvictParams(num_tokens=needed))
+            self.evict_for_alloc(EvictParams(num_tokens=needed))
-            if result.num_tokens_evicted < needed:
+            if self._component_available_size(ComponentType.FULL) < kv_tokens:
                 self.dec_lock_ref(node_id, ancestor_lock_params)
                 self.dec_host_lock_ref(node_id, host_anchor_params)
                 return False

python/sglang/srt/session/streaming_session.py

@@ -417,6 +417,9 @@ class StreamingSession(BasePrefixCache):
     def evict(self, params: EvictParams) -> EvictResult:
         return self.inner.evict(params)
 
+    def evict_for_alloc(self, params: EvictParams) -> EvictResult:
+        return self.inner.evict_for_alloc(params)
+
     def inc_lock_ref(self, node: Any) -> IncLockRefResult:
         result = self.try_inc_lock_ref(node)
         if result is not None:

test/registered/unit/hardware_backend/mlx/test_attention_patching.py

@@ -877,6 +877,17 @@ class TestMlxAuxiliaryStateRunnerCache(unittest.TestCase):
         self.assertEqual(forked.tolist(), [3])
         self.assertEqual(restored[0].state[0].tolist(), [1.0])
         self.assertEqual(pool.available_size(), 3)
+        self.assertEqual(pool.schedulable_available_size(), 3)
+
+    def test_auxiliary_state_pool_returns_unused_group_slots(self):
+        pool = MlxAuxiliaryStatePool(size=4, device="cpu")
+
+        pool.alloc_group_begin(3)
+        allocated = pool.alloc(1)
+        pool.alloc_group_end()
+
+        self.assertEqual(allocated.tolist(), [1])
+        self.assertEqual(pool.available_size(), 3)
 
     def test_auxiliary_state_pool_restores_instance_meta_state(self):
         pool = MlxAuxiliaryStatePool(size=2, device="cpu")
@@ -916,6 +927,7 @@ class TestMlxAuxiliaryStateRunnerCache(unittest.TestCase):
         self.assertIsNotNone(auxiliary_state_idx)
         self.assertIsNone(req.req_pool_idx)
         self.assertIsNotNone(req.mamba_pool_idx)
+        self.assertIs(pool.mamba_allocator, pool.mamba_pool)
         self.assertEqual(pool.auxiliary_state_pool.available_size(), 3)
         pool.free_auxiliary_state_cache(req)
         self.assertIsNone(req.mamba_pool_idx)

test/registered/unit/mem_cache/test_decode_radix_lock_ref.py

@@ -144,7 +144,7 @@ class TestDecodeLockRefScenarios(unittest.TestCase):
         error = queue._reclaim_swa_tail_capacity(129, "req-1")
 
         self.assertIsNone(error)
-        params = queue.tree_cache.evict.call_args.args[0]
+        params = queue.tree_cache.evict_for_alloc.call_args.args[0]
         self.assertEqual(params.num_tokens, 0)
         self.assertEqual(params.swa_num_tokens, 128)
 

test/registered/unit/mem_cache/test_hybrid_pool_assembler.py

@@ -2,9 +2,12 @@
 
 import unittest
 from types import SimpleNamespace
-from unittest.mock import patch
+from unittest.mock import MagicMock, patch
 
+from sglang.srt.mem_cache.base_prefix_cache import EvictParams
 from sglang.srt.mem_cache.hybrid_cache.hybrid_pool_assembler import (
+    _evict_mamba_for_device_alloc,
+    _evict_swa_for_device_alloc,
     _split_hicache_size,
     build_full_draft_pools,
 )
@@ -23,6 +26,40 @@ class _Pool:
         return self._kv_bytes
 
 
+class TestDeviceAllocEviction(CustomTestCase):
+    def test_swa_evicts_only_allocation_shortfall(self):
+        cache = MagicMock()
+        cache.token_to_kv_pool_allocator.swa_available_size.return_value = 8
+
+        _evict_swa_for_device_alloc(cache, required_size=10)
+
+        cache.evict_for_alloc.assert_called_once_with(EvictParams(swa_num_tokens=2))
+        cache.evict.assert_not_called()
+
+    def test_mamba_evicts_only_allocation_shortfall(self):
+        cache = MagicMock()
+        allocator = cache.req_to_token_pool.mamba_allocator
+        allocator.schedulable_available_size.return_value = 8
+
+        _evict_mamba_for_device_alloc(cache, required_size=10)
+
+        cache.evict_for_alloc.assert_called_once_with(EvictParams(mamba_num=2))
+        cache.evict.assert_not_called()
+
+    def test_sufficient_capacity_skips_eviction(self):
+        cache = MagicMock()
+        cache.token_to_kv_pool_allocator.swa_available_size.return_value = 10
+        cache.req_to_token_pool.mamba_allocator.schedulable_available_size.return_value = (
+            10
+        )
+
+        _evict_swa_for_device_alloc(cache, required_size=10)
+        _evict_mamba_for_device_alloc(cache, required_size=10)
+
+        cache.evict_for_alloc.assert_not_called()
+        cache.evict.assert_not_called()
+
+
 class TestSplitHicacheSize(CustomTestCase):
     def test_splits_total_budget_by_device_bytes(self):
         # scalar and (k, v) tuple return shapes both supported

test/registered/unit/mem_cache/test_mamba_donated_alloc_ratio.py

@@ -55,10 +55,10 @@ class _RatioCache:
         self.component_evictable_size_ = {ComponentType.MAMBA: 0}
         self.component_protected_size_ = {ComponentType.MAMBA: 0}
         self.prefix_nodes = []
+        self.alloc_evict_params = []
 
-    def evict(self, params: EvictParams):
+    def evict_for_alloc(self, params: EvictParams):
-        # Reclaim up to mamba_num evictable (unlocked) prefix snapshots, mirroring
+        self.alloc_evict_params.append(params)
-        # what the real tree eviction can hand back under mamba pressure.
         need = params.mamba_num
         for node in list(self.prefix_nodes):
             if need <= 0:
@@ -130,7 +130,9 @@ class TestMambaRatioEnvGate(unittest.TestCase):
                 return KVCacheConfigurator._calculate_mamba_ratio(fake)
 
     def test_flag_off_restores_original_ratios(self):
-        r = lambda **kw: self._ratio(skip=False, **kw)
+        def r(**kwargs):
+            return self._ratio(skip=False, **kwargs)
+
         self.assertEqual(
             r(extra_buffer=False, lazy=False, disable_overlap=True), 3
         )  # no_buffer
@@ -142,7 +144,9 @@ class TestMambaRatioEnvGate(unittest.TestCase):
         )  # overlap
 
     def test_flag_on_drops_base_but_keeps_no_buffer(self):
-        r = lambda **kw: self._ratio(skip=True, **kw)
+        def r(**kwargs):
+            return self._ratio(skip=True, **kwargs)
+
         self.assertEqual(
             r(extra_buffer=False, lazy=False, disable_overlap=True), 3
         )  # no_buffer
@@ -212,9 +216,12 @@ class TestDecSwaLockSkip(unittest.TestCase):
 class TestMambaDonatedAllocRatio(unittest.TestCase):
     def test_prefill_peak_ratio2_exhausts_pool(self):
         # pool = 2N, all N prefixes admission-locked: no evictable victim.
-        component, _, _ = _build_peak(pool_size=2 * N, lock_prefixes=True)
+        component, cache, _ = _build_peak(pool_size=2 * N, lock_prefixes=True)
         with self.assertRaisesRegex(AssertionError, "Can not alloc mamba cache"):
             component._alloc_mamba_slot()
+        self.assertEqual(
+            cache.alloc_evict_params, [EvictParams(num_tokens=0, mamba_num=1)]
+        )
 
     def test_prefill_peak_ratio3_has_headroom(self):
         # pool = 3N: N free slots remain after own + locked prefix.
@@ -230,6 +237,9 @@ class TestMambaDonatedAllocRatio(unittest.TestCase):
         slot = component._alloc_mamba_slot()
         self.assertIsNotNone(slot)
         self.assertEqual(len(cache.prefix_nodes), N - 1)
+        self.assertEqual(
+            cache.alloc_evict_params, [EvictParams(num_tokens=0, mamba_num=1)]
+        )
 
 
 class TestPPMambaPoolSizing(unittest.TestCase):

test/registered/unit/mem_cache/test_unified_radix_allocation_eviction.py

@@ -0,0 +1,132 @@
+"""CPU-only tests for allocation-aware UnifiedRadixCache eviction."""
+
+import unittest
+from unittest.mock import MagicMock
+
+from sglang.srt.mem_cache.base_prefix_cache import EvictParams
+from sglang.srt.mem_cache.common import evict_from_tree_cache
+from sglang.srt.mem_cache.unified_cache.components import ComponentType
+from sglang.srt.mem_cache.unified_radix_cache import UnifiedRadixCache
+from sglang.test.ci.ci_register import register_cpu_ci
+from sglang.test.test_utils import CustomTestCase
+
+register_cpu_ci(est_time=2, suite="base-a-test-cpu")
+
+
+class TestUnifiedRadixAllocationEviction(CustomTestCase):
+    @staticmethod
+    def _build_cache(*, collateral_capacity_gain: int):
+        cache = object.__new__(UnifiedRadixCache)
+        cache.disable = False
+        cache.tree_components = (ComponentType.FULL, ComponentType.MAMBA)
+        cache.is_swa_enabled = False
+        cache.cache_controller = None
+        cache.metrics_collector = None
+        cache.tree_core = MagicMock()
+
+        capacity = {"available": 30}
+        allocator = MagicMock()
+        allocator.available_size.side_effect = lambda: capacity["available"]
+        cache.token_to_kv_pool_allocator = allocator
+        cache.req_to_token_pool = MagicMock()
+
+        leaf_count = {"value": 0}
+
+        def next_node(component_type, tracker):
+            if tracker[component_type] >= 70:
+                return None, False
+            return leaf_count["value"] + 1, True
+
+        def evict_leaf(_node_id, tracker):
+            leaf_count["value"] += 1
+            tracker[ComponentType.FULL] += 20
+            tracker[ComponentType.MAMBA] += 1
+            capacity["available"] += (
+                collateral_capacity_gain if leaf_count["value"] == 1 else 20
+            )
+            return None
+
+        cache._evict_device_next_node = MagicMock(side_effect=next_node)
+        cache._evict_device_leaf = MagicMock(side_effect=evict_leaf)
+        return cache, capacity, leaf_count
+
+    def test_allocation_eviction_stops_when_shared_capacity_is_sufficient(self):
+        cache, capacity, leaf_count = self._build_cache(collateral_capacity_gain=70)
+
+        result = cache.evict_for_alloc(EvictParams(num_tokens=70))
+
+        self.assertEqual(capacity["available"], 100)
+        self.assertEqual(leaf_count["value"], 1)
+        self.assertEqual(result.num_tokens_evicted, 20)
+        self.assertEqual(result.mamba_num_evicted, 1)
+
+    def test_explicit_evict_preserves_component_count_semantics(self):
+        cache, _, leaf_count = self._build_cache(collateral_capacity_gain=70)
+
+        result = cache.evict(EvictParams(num_tokens=70))
+
+        self.assertEqual(leaf_count["value"], 4)
+        self.assertEqual(result.num_tokens_evicted, 80)
+        self.assertEqual(result.mamba_num_evicted, 4)
+
+    def test_c128_component_keeps_zero_quota(self):
+        cache, _, _ = self._build_cache(collateral_capacity_gain=70)
+        cache.tree_components = (ComponentType.FULL, ComponentType.C128)
+        cache._evict_device_next_node.side_effect = None
+        cache._evict_device_next_node.return_value = (None, False)
+
+        result = cache.evict(EvictParams(num_tokens=1))
+
+        self.assertEqual(result.num_tokens_evicted, 0)
+        cache.tree_core.evict_device_start.assert_called_once_with(
+            ComponentType.FULL, 1
+        )
+
+    def test_mamba_allocation_counts_collateral_full_capacity(self):
+        cache = object.__new__(UnifiedRadixCache)
+        cache.disable = False
+        cache.tree_components = (ComponentType.FULL, ComponentType.MAMBA)
+        cache.is_swa_enabled = False
+        cache.cache_controller = None
+        cache.metrics_collector = None
+        cache.tree_core = MagicMock()
+        cache.token_to_kv_pool_allocator = MagicMock()
+
+        capacity = {"available": 0}
+        mamba_allocator = MagicMock()
+        mamba_allocator.schedulable_available_size.side_effect = lambda: capacity[
+            "available"
+        ]
+        cache.req_to_token_pool = MagicMock(mamba_allocator=mamba_allocator)
+
+        def next_node(component_type, tracker):
+            return (None, False) if tracker[component_type] >= 3 else (1, True)
+
+        def evict_leaf(_node_id, tracker):
+            tracker[ComponentType.FULL] += 20
+            tracker[ComponentType.MAMBA] += 1
+            capacity["available"] += 3
+            return None
+
+        cache._evict_device_next_node = MagicMock(side_effect=next_node)
+        cache._evict_device_leaf = MagicMock(side_effect=evict_leaf)
+
+        result = cache.evict_for_alloc(EvictParams(mamba_num=3))
+
+        self.assertEqual(capacity["available"], 3)
+        self.assertEqual(result.num_tokens_evicted, 20)
+        self.assertEqual(result.mamba_num_evicted, 1)
+
+    def test_common_helper_uses_allocation_aware_entry_point(self):
+        tree_cache = MagicMock()
+        tree_cache.is_chunk_cache.return_value = False
+        tree_cache.token_to_kv_pool_allocator.available_size.return_value = 30
+
+        evict_from_tree_cache(tree_cache, num_tokens=100)
+
+        tree_cache.evict_for_alloc.assert_called_once_with(EvictParams(num_tokens=70))
+        tree_cache.evict.assert_not_called()
+
+
+if __name__ == "__main__":
+    unittest.main()

test/registered/unit/mem_cache/test_unified_radix_cache_unittest.py

@@ -343,6 +343,7 @@ def build_fixture(
     cfg: CacheConfig,
     *,
     enable_kv_cache_events: bool = False,
+    enable_session_radix_cache: bool = False,
     tree_page_size: Optional[int] = None,
     mamba_cache_chunk_size: Optional[int] = None,
 ):
@@ -472,6 +473,7 @@ def build_fixture(
         tree_components=cfg.components,
         enable_mamba_extra_buffer=cfg.enable_mamba_extra_buffer,
         enable_kv_cache_events=enable_kv_cache_events,
+        enable_session_radix_cache=enable_session_radix_cache,
         eviction_policy=cfg.eviction_policy,
         is_eagle=cfg.is_eagle,
     )
@@ -481,6 +483,162 @@ def build_fixture(
     return cache, allocator, req_to_token_pool
 
 
+@unittest.skipUnless(torch.cuda.is_available(), "cache fixtures need CUDA")
+class TestUnifiedRadixAllocationEvictionRealComponents(CustomTestCase):
+    """Allocation targets are observed between real auxiliary-tree steps."""
+
+    _SHORTFALL = 100
+
+    def _insert(self, cache, allocator, req_to_token_pool, tokens) -> None:
+        value = allocator.alloc(len(tokens))
+        self.assertIsNotNone(value)
+        params = InsertParams(
+            key=RadixKey(array("q", tokens)),
+            value=value[: len(tokens)],
+        )
+        if cache.supports_mamba():
+            req = Req(
+                rid=f"mamba-{len(tokens)}",
+                origin_input_text="",
+                origin_input_ids=array("q"),
+                sampling_params=SamplingParams(temperature=0, max_new_tokens=1),
+            )
+            req_to_token_pool.alloc([req])
+            params.mamba_value = req.mamba_pool_idx.unsqueeze(0)
+        cache.insert(params)
+
+    def _build_internal_chain(self, component_type, enable_session_radix_cache):
+        cfg = (
+            CacheConfig(
+                components=(ComponentType.FULL, ComponentType.SWA),
+                sliding_window_size=128,
+            )
+            if component_type is ComponentType.SWA
+            else CacheConfig(
+                components=(ComponentType.FULL, ComponentType.MAMBA),
+                mamba_cache_size=8,
+            )
+        )
+        cache, allocator, req_to_token_pool = build_fixture(
+            cfg, enable_session_radix_cache=enable_session_radix_cache
+        )
+        for length in (2, 4, 6):
+            self._insert(
+                cache,
+                allocator,
+                req_to_token_pool,
+                list(range(1, length + 1)),
+            )
+
+        lru = cache.tree_core.lru_lists[component_type]
+        first = lru.get_lru_no_lock()
+        second = lru.get_prev_no_lock(first)
+        leaf = lru.get_prev_no_lock(second)
+        self.assertNotIn(first, cache.tree_core.evictable_device_leaves)
+        self.assertNotIn(second, cache.tree_core.evictable_device_leaves)
+        self.assertIn(leaf, cache.tree_core.evictable_device_leaves)
+        for node in (first, second, leaf):
+            self.assertIsNotNone(node.component_data[component_type].value)
+            self.assertIsNotNone(node.component_data[ComponentType.FULL].value)
+        return cache, first, second, leaf
+
+    def _evict_for_alloc_after_first_drain(self, cache, component_type):
+        capacity = {"available": 0}
+        auxiliary_drains = {"count": 0}
+        real_available_size = cache._component_available_size
+        real_free_values = cache._free_values
+
+        def available_size(requested_type):
+            if requested_type is component_type:
+                return capacity["available"]
+            return real_available_size(requested_type)
+
+        def free_values(device_frees, host_frees):
+            freed_auxiliary = bool(device_frees.get(component_type))
+            real_free_values(device_frees, host_frees)
+            if freed_auxiliary:
+                auxiliary_drains["count"] += 1
+                capacity["available"] = self._SHORTFALL
+
+        params = (
+            EvictParams(swa_num_tokens=self._SHORTFALL)
+            if component_type is ComponentType.SWA
+            else EvictParams(mamba_num=self._SHORTFALL)
+        )
+        with (
+            mock.patch.object(
+                cache, "_component_available_size", side_effect=available_size
+            ),
+            mock.patch.object(cache, "_free_values", side_effect=free_values),
+        ):
+            result = cache.evict_for_alloc(params)
+        return result, auxiliary_drains["count"]
+
+    def test_allocation_target_stops_after_one_internal_tombstone(self):
+        for component_type in (ComponentType.SWA, ComponentType.MAMBA):
+            for enable_session_radix_cache in (False, True):
+                with self.subTest(
+                    component_type=component_type,
+                    enable_session_radix_cache=enable_session_radix_cache,
+                ):
+                    cache, first, second, leaf = self._build_internal_chain(
+                        component_type, enable_session_radix_cache
+                    )
+                    first_size = len(first.component_data[component_type].value)
+
+                    result, drain_count = self._evict_for_alloc_after_first_drain(
+                        cache, component_type
+                    )
+
+                    self.assertIsNone(first.component_data[component_type].value)
+                    self.assertIsNotNone(second.component_data[component_type].value)
+                    self.assertIsNotNone(leaf.component_data[component_type].value)
+                    self.assertIsNotNone(leaf.component_data[ComponentType.FULL].value)
+                    self.assertEqual(result.num_tokens_evicted, 0)
+                    self.assertEqual(drain_count, 1)
+                    evicted = (
+                        result.swa_num_tokens_evicted
+                        if component_type is ComponentType.SWA
+                        else result.mamba_num_evicted
+                    )
+                    self.assertEqual(evicted, first_size)
+                    cache.sanity_check()
+
+    def test_explicit_evict_continues_across_internal_steps(self):
+        for component_type in (ComponentType.SWA, ComponentType.MAMBA):
+            for enable_session_radix_cache in (False, True):
+                with self.subTest(
+                    component_type=component_type,
+                    enable_session_radix_cache=enable_session_radix_cache,
+                ):
+                    cache, first, second, leaf = self._build_internal_chain(
+                        component_type, enable_session_radix_cache
+                    )
+                    request_count = sum(
+                        len(node.component_data[component_type].value)
+                        for node in (first, second)
+                    )
+                    params = (
+                        EvictParams(swa_num_tokens=request_count)
+                        if component_type is ComponentType.SWA
+                        else EvictParams(mamba_num=request_count)
+                    )
+
+                    result = cache.evict(params)
+
+                    self.assertIsNone(first.component_data[component_type].value)
+                    self.assertIsNone(second.component_data[component_type].value)
+                    self.assertIsNotNone(leaf.component_data[component_type].value)
+                    self.assertIsNotNone(leaf.component_data[ComponentType.FULL].value)
+                    evicted = (
+                        result.swa_num_tokens_evicted
+                        if component_type is ComponentType.SWA
+                        else result.mamba_num_evicted
+                    )
+                    self.assertEqual(evicted, request_count)
+                    cache.sanity_check()
+
+
 class TestUnifiedRadixCacheEagleHiCacheStorageKey(CustomTestCase):
     cfg = CacheConfig(
         page_size=4,
@@ -5363,10 +5521,12 @@ class UnifiedRadixCacheSuite:
                 "alloc",
                 side_effect=[None, retry_slot],
             ),
-            mock.patch.object(cache, "evict", autospec=True) as evict,
+            mock.patch.object(
+                cache, "evict_for_alloc", autospec=True
+            ) as evict_for_alloc,
         ):
             prep = comp.prepare_load_back(leaf.id, req=req)
-        evict.assert_called_once_with(EvictParams(num_tokens=0, mamba_num=1))
+        evict_for_alloc.assert_called_once_with(EvictParams(num_tokens=0, mamba_num=1))
         self.assertIs(prep.allocated_mamba_slot, retry_slot)
         self.assertEqual(int(req.mamba_pool_idx), int(retry_slot[0]))
 
@@ -5790,13 +5950,15 @@ class UnifiedRadixCacheSuite:
             int(swa_xfer.host_indices.numel()),
         )
 
-        with mock.patch.object(cache, "evict", wraps=cache.evict) as evict_mock:
+        with mock.patch.object(
+            cache, "evict_for_alloc", wraps=cache.evict_for_alloc
+        ) as evict_for_alloc_mock:
             self.assertTrue(cache.load_back(leaf.id))
 
         # Full pre-eviction must not be triggered by SWA pool pressure.
         full_pre_evict_calls = [
             call
-            for call in evict_mock.call_args_list
+            for call in evict_for_alloc_mock.call_args_list
             if call.args and call.args[0].num_tokens > 0
         ]
         self.assertEqual(full_pre_evict_calls, [])
@@ -5807,7 +5969,7 @@ class UnifiedRadixCacheSuite:
                 call.args
                 and call.args[0].num_tokens == 0
                 and call.args[0].swa_num_tokens > 0
-                for call in evict_mock.call_args_list
+                for call in evict_for_alloc_mock.call_args_list
             )
         )
 
@@ -7026,9 +7188,13 @@ class TestReturnedValuesDrain(_InsertWalkSuite):
         cases = [
             (
                 "evict_device_next_node",
-                lambda: make(EvictDeviceNextNodeResult, node_id=node.id),
+                lambda: make(
+                    EvictDeviceNextNodeResult,
+                    node_id=node.id,
+                    made_progress=True,
+                ),
                 lambda: cache._evict_device_next_node(ComponentType.FULL, tracker),
-                node.id,
+                (node.id, True),
             ),
             (
                 "evict_device_leaf",