hiradix_cache.py

import heapq
import logging
import threading
import time
from queue import Queue
from typing import List, Optional

import torch

from sglang.srt.managers.cache_controller import HiCacheController, PrefetchOperation
from sglang.srt.mem_cache.allocator import BaseTokenToKVPoolAllocator
from sglang.srt.mem_cache.base_prefix_cache import MatchResult
from sglang.srt.mem_cache.memory_pool import (
    MHATokenToKVPool,
    MLATokenToKVPool,
    ReqToTokenPool,
)
from sglang.srt.mem_cache.memory_pool_host import (
    MHATokenToKVPoolHost,
    MLATokenToKVPoolHost,
)
from sglang.srt.mem_cache.radix_cache import RadixCache, TreeNode
from sglang.srt.metrics.collector import StorageMetricsCollector

logger = logging.getLogger(__name__)


class HiRadixCache(RadixCache):

    def __init__(
        self,
        req_to_token_pool: ReqToTokenPool,
        token_to_kv_pool_allocator: BaseTokenToKVPoolAllocator,
        tp_cache_group: torch.distributed.ProcessGroup,
        page_size: int,
        hicache_ratio: float,
        hicache_size: int,
        hicache_write_policy: str,
        hicache_io_backend: str,
        hicache_mem_layout: str,
        enable_metrics: bool,
        hicache_storage_backend: Optional[str] = None,
        hicache_storage_prefetch_policy: Optional[str] = "best_effort",
        model_name: Optional[str] = None,
        storage_backend_extra_config: Optional[str] = None,
    ):

        if hicache_io_backend == "direct":
            if hicache_mem_layout == "page_first":
                hicache_mem_layout = "layer_first"
                logger.warning(
                    "Page first layout is not supported with direct IO backend, switching to layer first layout"
                )

        self.kv_cache = token_to_kv_pool_allocator.get_kvcache()
        if isinstance(self.kv_cache, MHATokenToKVPool):
            self.token_to_kv_pool_host = MHATokenToKVPoolHost(
                self.kv_cache,
                hicache_ratio,
                hicache_size,
                page_size,
                hicache_mem_layout,
            )
        elif isinstance(self.kv_cache, MLATokenToKVPool):
            self.token_to_kv_pool_host = MLATokenToKVPoolHost(
                self.kv_cache,
                hicache_ratio,
                hicache_size,
                page_size,
                hicache_mem_layout,
            )
        else:
            raise ValueError(f"HiRadixCache only supports MHA and MLA yet")

        self.tp_group = tp_cache_group
        self.tp_world_size = torch.distributed.get_world_size(group=self.tp_group)
        self.enable_storage = hicache_storage_backend is not None
        self.enable_storage_metrics = self.enable_storage and enable_metrics

        # todo: customizable storage prefetch threshold and timeout
        self.prefetch_threshold = 256
        self.prefetch_timeout = 3  # seconds
        self.prefetch_stop_policy = hicache_storage_prefetch_policy

        self.load_cache_event = threading.Event()
        self.cache_controller = HiCacheController(
            token_to_kv_pool_allocator,
            self.token_to_kv_pool_host,
            page_size,
            self.tp_group,
            load_cache_event=self.load_cache_event,
            write_policy=hicache_write_policy,
            io_backend=hicache_io_backend,
            storage_backend=hicache_storage_backend,
            prefetch_threshold=self.prefetch_threshold,
            model_name=model_name,
            storage_backend_extra_config=storage_backend_extra_config,
        )
        if self.enable_storage_metrics:
            # TODO: support pp
            labels = {
                "storage_backend": hicache_storage_backend,
                "tp_rank": self.cache_controller.tp_rank,
                "dp_rank": self.cache_controller.dp_rank,
            }
            self.metrics_collector = StorageMetricsCollector(labels=labels)

        # record the nodes with ongoing write through
        self.ongoing_write_through = {}
        # record the node segments with ongoing load back
        self.ongoing_load_back = {}
        # record the ongoing prefetch requests
        self.ongoing_prefetch = {}
        self.ongoing_backup = {}
        # todo: dynamically adjust the threshold
        self.write_through_threshold = (
            1 if hicache_write_policy == "write_through" else 2
        )
        self.load_back_threshold = 10
        super().__init__(
            req_to_token_pool, token_to_kv_pool_allocator, page_size, disable=False
        )

    def reset(self):
        TreeNode.counter = 0
        self.cache_controller.reset()
        self.token_to_kv_pool_host.clear()
        super().reset()

    def get_height(self, node: TreeNode):
        height = 0
        while node != self.root_node:
            node = node.parent
            height += 1
        return height

    def clear_storage_backend(self) -> bool:
        if self.enable_storage:
            try:
                # Check if the storage backend has a clear method (for nixl backends)
                if hasattr(self.cache_controller.storage_backend, "clear"):
                    self.cache_controller.storage_backend.clear()
                    logger.info(
                        "Hierarchical cache storage backend cleared successfully!"
                    )
                    return True
                else:
                    logger.warning(
                        f"Storage backend {type(self.cache_controller.storage_backend).__name__} does not support clear operation."
                    )
                    return False
            except Exception as e:
                logger.error(f"Failed to clear hierarchical cache storage backend: {e}")
                return False
        else:
            logger.warning("Hierarchical cache storage backend is not enabled.")
            return False

    def write_backup(self, node: TreeNode, write_back=False):
        host_indices = self.cache_controller.write(
            device_indices=node.value,
            node_id=node.id,
        )
        if host_indices is None:
            self.evict_host(len(node.value))
            host_indices = self.cache_controller.write(
                device_indices=node.value,
                node_id=node.id,
            )
        if host_indices is not None:
            node.host_value = host_indices
            assert len(node.host_value) > 0
            self.ongoing_write_through[node.id] = node
            if not write_back:
                # no need to lock nodes if write back
                self.inc_lock_ref(node)
        else:
            return 0

        return len(host_indices)

    def write_backup_storage(self, node: TreeNode):
        operation_id = self.cache_controller.write_storage(
            node.host_value, node.key, node.hash_value
        )
        self.ongoing_backup[operation_id] = node
        node.protect_host()

    def _inc_hit_count(self, node: TreeNode, chunked=False):
        # skip the hit count update for chunked requests
        if self.cache_controller.write_policy == "write_back" or chunked:
            return
        node.hit_count += 1

        if not node.backuped:
            if node.hit_count >= self.write_through_threshold:
                # write to host if the node is not backuped
                self.write_backup(node)

    def writing_check(self, write_back=False):
        if write_back:
            # blocking till all write back complete
            while len(self.ongoing_write_through) > 0:
                ack_id = self.cache_controller.ack_write_queue.get()
                del self.ongoing_write_through[ack_id]
            return
        queue_size = torch.tensor(
            self.cache_controller.ack_write_queue.qsize(), dtype=torch.int
        )
        if self.tp_world_size > 1:
            # synchrnoize TP workers to make the same update to radix cache
            torch.distributed.all_reduce(
                queue_size,
                op=torch.distributed.ReduceOp.MIN,
                group=self.tp_group,
            )
        for _ in range(queue_size.item()):
            ack_id = self.cache_controller.ack_write_queue.get()
            backuped_node = self.ongoing_write_through[ack_id]
            self.dec_lock_ref(backuped_node)
            del self.ongoing_write_through[ack_id]
            if self.enable_storage:
                self.write_backup_storage(backuped_node)

    def loading_check(self):
        while not self.cache_controller.ack_load_queue.empty():
            try:
                ack_id = self.cache_controller.ack_load_queue.get_nowait()
                start_node, end_node = self.ongoing_load_back[ack_id]
                self.dec_lock_ref(end_node)
                while end_node != start_node:
                    assert end_node.loading
                    end_node.loading = False
                    end_node = end_node.parent
                # clear the reference
                del self.ongoing_load_back[ack_id]
            except Exception:
                break

    def evictable_size(self):
        return self.evictable_size_

    def evict(self, num_tokens: int):
        leaves = self._collect_leaves_device()
        heapq.heapify(leaves)

        num_evicted = 0
        write_back_nodes = []
        while num_evicted < num_tokens and len(leaves):
            x = heapq.heappop(leaves)

            if x.lock_ref > 0:
                continue

            if not x.backuped:
                if self.cache_controller.write_policy == "write_back":
                    # write to host if the node is not backuped
                    num_evicted += self.write_backup(x, write_back=True)
                    write_back_nodes.append(x)
                else:
                    num_evicted += self._evict_regular(x)
            else:
                num_evicted += self._evict_backuped(x)

            for child in x.parent.children.values():
                if child in write_back_nodes:
                    continue
                if not child.evicted:
                    break
            else:
                # all children are evicted or no children
                heapq.heappush(leaves, x.parent)

        if self.cache_controller.write_policy == "write_back":
            self.writing_check(write_back=True)
            for node in write_back_nodes:
                assert node.backuped
                self._evict_backuped(node)

    def _evict_backuped(self, node: TreeNode):
        # evict a node already written to host
        num_evicted = self.cache_controller.evict_device(node.value, node.host_value)
        assert num_evicted > 0
        self.evictable_size_ -= num_evicted
        node.value = None
        return num_evicted

    def _evict_regular(self, node: TreeNode):
        # evict a node not initiated write to host
        self.cache_controller.mem_pool_device_allocator.free(node.value)
        num_evicted = len(node.value)
        self._delete_leaf(node)
        return num_evicted

    def evict_host(self, num_tokens: int):
        leaves = self._collect_leaves()
        heapq.heapify(leaves)

        num_evicted = 0
        while num_evicted < num_tokens and len(leaves):
            x = heapq.heappop(leaves)
            if x == self.root_node:
                break
            # only evict the host value of evicted nodes
            if not x.evicted:
                continue

            # node is protected from eviction as it has ongoing prefetch or backup to storage
            if x.host_ref_counter > 0:
                continue

            num_evicted += self.cache_controller.evict_host(x.host_value)

            for k, v in x.parent.children.items():
                if v == x:
                    break
            del x.parent.children[k]

            if len(x.parent.children) == 0 and x.parent.evicted:
                heapq.heappush(leaves, x.parent)

    def load_back(
        self, node: TreeNode, mem_quota: Optional[int] = None
    ) -> Optional[torch.Tensor]:
        # todo: more loading policies

        last_hit_node = node
        nodes_to_load = []
        while node.evicted:
            assert (
                node.backuped
            ), "No backup available on evicted nodes, should not happen"
            nodes_to_load.insert(0, node)
            node = node.parent
        else:
            ancester_node = node

        # protect the ancestor nodes from eviction
        delta = self.inc_lock_ref(ancester_node)

        # load it all or not at all
        host_indices = torch.cat([n.host_value for n in nodes_to_load])
        if len(host_indices) < self.load_back_threshold or (
            len(host_indices) > mem_quota + delta if mem_quota is not None else False
        ):
            # skip loading back if the total size is too small or exceeding the memory quota
            self.dec_lock_ref(ancester_node)
            return None

        device_indices = self.cache_controller.load(
            host_indices=host_indices, node_id=last_hit_node.id
        )
        if device_indices is None:
            self.evict(len(host_indices))
            device_indices = self.cache_controller.load(
                host_indices=host_indices, node_id=last_hit_node.id
            )
        self.dec_lock_ref(ancester_node)
        if device_indices is None:
            # no sufficient GPU memory to load back KV caches
            return None

        self.ongoing_load_back[last_hit_node.id] = (ancester_node, last_hit_node)
        offset = 0
        for node in nodes_to_load:
            node.value = device_indices[offset : offset + len(node.host_value)]
            offset += len(node.host_value)
            node.loading = True
        self.evictable_size_ += len(device_indices)
        self.inc_lock_ref(last_hit_node)

        return device_indices

    def init_load_back(
        self,
        last_node: TreeNode,
        host_hit_length: int,
        mem_quota: Optional[int] = None,
    ):
        _ = host_hit_length  # unused, but kept for compatibility
        if last_node.evicted:
            loading_values = self.load_back(last_node, mem_quota)
            if loading_values is not None:
                logger.debug(
                    f"loading back {len(loading_values)} tokens for node {last_node.id}"
                )
                return loading_values, last_node

            while last_node.evicted:
                last_node = last_node.parent

        return (
            torch.empty((0,), dtype=torch.int64, device=self.device),
            last_node,
        )

    def ready_to_load_host_cache(self):
        producer_index = self.cache_controller.layer_done_counter.next_producer()
        self.load_cache_event.set()
        return producer_index

    def check_hicache_events(self):
        self.writing_check()
        self.loading_check()
        if self.enable_storage:
            self.drain_storage_control_queues()
        if self.enable_storage_metrics:
            self.metrics_collector.log_storage_metrics(
                self.cache_controller.storage_backend.get_stats()
            )

    def drain_storage_control_queues(self):
        """
        Combine prefetch revoke, backup ack, and host mem release checks
        to minimize TP synchronization and Python overhead.
        """
        cc = self.cache_controller

        qsizes = torch.tensor(
            [
                cc.prefetch_revoke_queue.qsize(),
                cc.ack_backup_queue.qsize(),
                cc.host_mem_release_queue.qsize(),
            ],
            dtype=torch.int,
        )
        if self.tp_world_size > 1:
            torch.distributed.all_reduce(
                qsizes, op=torch.distributed.ReduceOp.MIN, group=self.tp_group
            )

        n_revoke, n_backup, n_release = map(int, qsizes.tolist())

        # process prefetch revokes
        for _ in range(n_revoke):
            req_id = cc.prefetch_revoke_queue.get()
            info = self.ongoing_prefetch.pop(req_id, None)
            if info is not None:
                last_host_node, token_ids, _, _ = info
                last_host_node.release_host()
                cc.prefetch_tokens_occupied -= len(token_ids)
            # else: the revoked operation already got terminated, nothing to do

        # process backup acks
        for _ in range(n_backup):
            operation = cc.ack_backup_queue.get()
            ack_id = operation.id
            entry = self.ongoing_backup.pop(ack_id, None)
            if entry is not None:
                entry.release_host()
            if self.enable_storage_metrics:
                self.metrics_collector.log_backuped_tokens(operation.completed_tokens)

        # release host memory
        host_indices_list = []
        for _ in range(n_release):
            host_indices_list.append(cc.host_mem_release_queue.get())
        if host_indices_list:
            host_indices = torch.cat(host_indices_list, dim=0)
            cc.mem_pool_host.free(host_indices)

    def can_terminate_prefetch(self, operation: PrefetchOperation):
        can_terminate = True

        if self.prefetch_stop_policy == "best_effort":
            return can_terminate

        if len(operation.hash_value) == 0:
            completed = False
        else:
            completed = (
                operation.completed_tokens == len(operation.hash_value) * self.page_size
            )

        if self.prefetch_stop_policy == "wait_complete":
            can_terminate = completed
        elif self.prefetch_stop_policy == "timeout":
            can_terminate = completed or (
                time.monotonic() - operation.start_time > self.prefetch_timeout
            )
        else:
            # unknown prefetch stop policy, just return True
            return True

        operation_terminated = operation.is_terminated()
        if self.tp_world_size > 1:
            states = torch.tensor(
                [1 - int(can_terminate), int(operation_terminated)],
                dtype=torch.int,
            )
            torch.distributed.all_reduce(
                states,
                op=torch.distributed.ReduceOp.MAX,
                group=self.tp_group,
            )
            can_terminate = states[0].item() == 0
            operation_terminated = states[1].item() == 1
        # the operation should be terminated if it is already terminated on any TP worker
        # or it meets the termination condition on all TP workers
        can_terminate = can_terminate or operation_terminated
        return can_terminate

    def check_prefetch_progress(self, req_id: str) -> bool:
        if req_id not in self.ongoing_prefetch:
            # there is no ongoing prefetch for this request or it has been revoked
            return True

        # todo: more policies for prefetch progress such as timeout
        # the current policy is to prefetch with best effort and terminate when queuing is over
        last_host_node, token_ids, host_indices, operation = self.ongoing_prefetch[
            req_id
        ]

        if operation.host_indices is None:
            # prefetch has not been issued due to insufficient host memory
            return True

        if not self.can_terminate_prefetch(operation):
            return False

        completed_tokens, hash_value = self.cache_controller.terminate_prefetch(
            operation
        )
        logger.debug(f"Prefetch {req_id} completed with {completed_tokens} tokens")

        min_completed_tokens = completed_tokens
        if self.tp_world_size > 1:
            # synchrnoize TP workers to make the same update to hiradix cache
            completed_tokens_tensor = torch.tensor(
                min_completed_tokens, dtype=torch.int
            )
            torch.distributed.all_reduce(
                completed_tokens_tensor,
                op=torch.distributed.ReduceOp.MIN,
                group=self.tp_group,
            )
            min_completed_tokens = completed_tokens_tensor.item()
        fetched_token_ids = token_ids[:min_completed_tokens]
        written_indices = host_indices[:min_completed_tokens]
        matched_length = self._insert_helper_host(
            last_host_node,
            fetched_token_ids,
            written_indices,
            hash_value[: min_completed_tokens // self.page_size],
        )
        if len(written_indices):
            self.cache_controller.mem_pool_host.update_prefetch(written_indices)

        self.cache_controller.mem_pool_host.free(host_indices[:matched_length])
        self.cache_controller.append_host_mem_release(
            host_indices[min_completed_tokens:completed_tokens]
        )
        last_host_node.release_host()
        del self.ongoing_prefetch[req_id]
        self.cache_controller.prefetch_tokens_occupied -= len(token_ids)

        if self.enable_storage_metrics:
            self.metrics_collector.log_prefetched_tokens(
                min_completed_tokens - matched_length
            )

        return True

    def match_prefix(self, key: List[int], **kwargs):
        empty_value = torch.empty((0,), dtype=torch.int64, device=self.device)
        if self.disable or len(key) == 0:
            return MatchResult(
                device_indices=empty_value,
                last_device_node=self.root_node,
                last_host_node=self.root_node,
                host_hit_length=0,
            )

        if self.page_size != 1:
            page_aligned_len = len(key) // self.page_size * self.page_size
            key = key[:page_aligned_len]

        value, last_node = self._match_prefix_helper(self.root_node, key)
        if value:
            value = torch.cat(value)
        else:
            value = empty_value

        host_hit_length = 0
        last_host_node = last_node
        while last_node.evicted:
            host_hit_length += len(last_node.host_value)
            last_node = last_node.parent
        while not last_host_node.backuped:
            last_host_node = last_host_node.parent

        return MatchResult(
            device_indices=value,
            last_device_node=last_node,
            last_host_node=last_host_node,
            host_hit_length=host_hit_length,
        )

    def prefetch_from_storage(
        self,
        req_id: str,
        last_host_node: TreeNode,
        new_input_tokens: List[int],
        last_hash: Optional[str] = None,
    ):
        # align the number of fetching tokens to the page size
        prefetch_length = len(new_input_tokens) - (
            len(new_input_tokens) % self.page_size
        )
        new_input_tokens = new_input_tokens[:prefetch_length]
        if (
            not self.enable_storage
            or prefetch_length < self.prefetch_threshold
            or self.cache_controller.prefetch_rate_limited()
        ):
            return

        last_host_node.protect_host()
        host_indices = self.cache_controller.mem_pool_host.alloc(prefetch_length)
        if host_indices is None:
            self.evict_host(prefetch_length)
            host_indices = self.cache_controller.mem_pool_host.alloc(prefetch_length)
        if host_indices is None:
            last_host_node.release_host()
            # no sufficient host memory for prefetch
            return
        operation = self.cache_controller.prefetch(
            req_id, host_indices, new_input_tokens, last_hash
        )
        self.ongoing_prefetch[req_id] = (
            last_host_node,
            new_input_tokens,
            host_indices,
            operation,
        )
        self.cache_controller.prefetch_tokens_occupied += len(new_input_tokens)

    def _insert_helper_host(self, node: TreeNode, key: List, host_value, hash_value):
        node.last_access_time = time.monotonic()
        if len(key) == 0:
            return 0

        child_key = self.get_child_key_fn(key)

        matched_length = 0
        while len(key) > 0 and child_key in node.children.keys():
            node = node.children[child_key]
            node.last_access_time = time.monotonic()
            prefix_len = self.key_match_fn(node.key, key)
            key = key[prefix_len:]
            host_value = host_value[prefix_len:]
            hash_value = hash_value[prefix_len // self.page_size :]
            matched_length += prefix_len

            if prefix_len < len(node.key):
                new_node = self._split_node(node.key, node, prefix_len)
                node = new_node

            if len(key):
                child_key = self.get_child_key_fn(key)

        if len(key):
            new_node = TreeNode()
            new_node.parent = node
            new_node.key = key
            new_node.value = None
            new_node.host_value = host_value
            new_node.hash_value = hash_value
            node.children[child_key] = new_node
        return matched_length

    def _match_prefix_helper(self, node: TreeNode, key: List):
        node.last_access_time = time.monotonic()
        child_key = self.get_child_key_fn(key)
        value = []

        while len(key) > 0 and child_key in node.children.keys():
            child = node.children[child_key]
            child.last_access_time = time.monotonic()
            prefix_len = self.key_match_fn(child.key, key)
            if prefix_len < len(child.key):
                new_node = self._split_node(child.key, child, prefix_len)
                if not new_node.evicted:
                    value.append(new_node.value)
                node = new_node
                break
            else:
                if not child.evicted:
                    value.append(child.value)
                node = child
                key = key[prefix_len:]

                if len(key):
                    child_key = self.get_child_key_fn(key)

        return value, node

    def _split_node(self, key, child: TreeNode, split_len: int):
        # child node split into new_node -> child
        new_node = TreeNode()
        new_node.children = {self.get_child_key_fn(key[split_len:]): child}
        new_node.parent = child.parent
        new_node.lock_ref = child.lock_ref
        new_node.key = child.key[:split_len]
        new_node.loading = child.loading
        new_node.hit_count = child.hit_count

        # split value and host value if exists
        if child.evicted:
            new_node.value = None
        else:
            new_node.value = child.value[:split_len]
            child.value = child.value[split_len:]
        if child.backuped:
            new_node.host_value = child.host_value[:split_len]
            child.host_value = child.host_value[split_len:]

        if child.hash_value:
            new_node.hash_value = child.hash_value[: split_len // self.page_size]
            child.hash_value = child.hash_value[split_len // self.page_size :]
        child.parent = new_node
        child.key = child.key[split_len:]
        new_node.parent.children[self.get_child_key_fn(key)] = new_node
        return new_node

    def insert(self, key: List, value, chunked=False):
        if len(key) == 0:
            return 0

        node = self.root_node
        child_key = self.get_child_key_fn(key)
        total_prefix_length = 0

        while len(key) > 0 and child_key in node.children.keys():
            node = node.children[child_key]
            node.last_access_time = time.monotonic()
            prefix_len = self.key_match_fn(node.key, key)

            if prefix_len == len(node.key):
                if node.evicted:
                    # change the reference if the node is evicted
                    # this often happens in the case of KV cache recomputation
                    node.value = value[:prefix_len]
                    self.token_to_kv_pool_host.update_synced(node.host_value)
                    self.evictable_size_ += len(node.value)
                else:
                    self._inc_hit_count(node, chunked)
                    total_prefix_length += prefix_len
            else:
                # partial match, split the node
                new_node = self._split_node(node.key, node, prefix_len)
                if new_node.evicted:
                    new_node.value = value[:prefix_len]
                    self.token_to_kv_pool_host.update_synced(new_node.host_value)
                    self.evictable_size_ += len(new_node.value)
                else:
                    self._inc_hit_count(new_node, chunked)
                    total_prefix_length += prefix_len
                node = new_node

            key = key[prefix_len:]
            value = value[prefix_len:]

            if len(key):
                child_key = self.get_child_key_fn(key)

        if len(key):
            new_node = TreeNode()
            new_node.parent = node
            new_node.key = key
            new_node.value = value
            node.children[child_key] = new_node
            self.evictable_size_ += len(value)

            if self.enable_storage:
                last_hash = node.get_last_hash_value()
                assert (node == self.root_node) or (
                    last_hash is not None
                ), "Parent node must have a hash value with storage enabled"
                new_node.hash_value = []
                for idx in range(0, len(key), self.page_size):
                    new_node.hash_value.append(
                        self.cache_controller.get_hash_str(
                            key[idx : idx + self.page_size],
                            prior_hash=last_hash,
                        )
                    )
                    last_hash = new_node.hash_value[-1]

            if self.cache_controller.write_policy != "write_back":
                self._inc_hit_count(new_node, chunked)
        return total_prefix_length

    def _collect_leaves_device(self):
        def is_leaf(node):
            if node.evicted:
                return False
            if node == self.root_node:
                return False
            if len(node.children) == 0:
                return True
            for child in node.children.values():
                if not child.evicted:
                    return False
            return True

        ret_list = []
        stack = [self.root_node]
        while stack:
            cur_node = stack.pop()
            if is_leaf(cur_node):
                ret_list.append(cur_node)
            else:
                for cur_child in cur_node.children.values():
                    if not cur_child.evicted:
                        stack.append(cur_child)
        return ret_list

    def release_aborted_request(self, rid: str):
        if rid not in self.ongoing_prefetch:
            return

        last_host_node, token_ids, host_indices, operation = self.ongoing_prefetch[rid]
        if operation.host_indices is None:
            return

        completed_tokens, _ = self.cache_controller.terminate_prefetch(operation)
        if self.tp_world_size > 1:
            torch.distributed.barrier(group=self.tp_group)
        last_host_node.release_host()
        del self.ongoing_prefetch[rid]
        self.cache_controller.append_host_mem_release(host_indices[:completed_tokens])
        self.cache_controller.prefetch_tokens_occupied -= len(token_ids)