[KV offload][1/N] Introduce an offloading component

.buildkite/test-pipeline.yaml

@@ -302,6 +302,7 @@ steps:
     # split the test to avoid interference
     - pytest -v -s v1/core
     - pytest -v -s v1/executor
+    - pytest -v -s v1/offloading
     - pytest -v -s v1/sample
     - pytest -v -s v1/logits_processors
     - pytest -v -s v1/worker

tests/v1/offloading/test_worker.py

@@ -0,0 +1,152 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+from vllm.v1.offloading.abstract import LoadStoreSpec
+from vllm.v1.offloading.worker.worker import (OffloadingHandler,
+                                              OffloadingWorker, TransferResult,
+                                              TransferSpec)
+
+
+class LoadStoreSpec1(LoadStoreSpec):
+
+    def __init__(self,
+                 submit_success: bool = True,
+                 async_success: bool = True,
+                 exception: bool = False):
+        self.finished = False
+        self.submit_success = submit_success
+        self.async_success = async_success
+        self.exception = exception
+
+    @staticmethod
+    def medium() -> str:
+        return "1"
+
+    def __repr__(self):
+        return f"{self.medium()}: {id(self)}"
+
+
+class LoadStoreSpec2(LoadStoreSpec):
+
+    @staticmethod
+    def medium() -> str:
+        return "2"
+
+    def __repr__(self):
+        return f"{self.medium()}: {id(self)}"
+
+
+class OffloadingHandler1To2(OffloadingHandler):
+
+    def __init__(self):
+        self.transfers: dict[int, LoadStoreSpec1] = {}
+
+    def transfer_async(self, job_id: int, spec: TransferSpec) -> bool:
+        src, dst = spec
+        assert isinstance(src, LoadStoreSpec1)
+        assert isinstance(dst, LoadStoreSpec2)
+
+        if src.exception:
+            raise Exception("An expected exception. Don't worry!")
+        if not src.submit_success:
+            return False
+
+        self.transfers[job_id] = src
+        return True
+
+    def get_finished(self) -> list[TransferResult]:
+        finished = []
+        for job_id, spec in list(self.transfers.items()):
+            if spec.finished:
+                finished.append((job_id, spec.async_success))
+                del self.transfers[job_id]
+        return finished
+
+
+class OffloadingHandler2To1(OffloadingHandler):
+
+    def __init__(self):
+        self.transfers: dict[int, LoadStoreSpec1] = {}
+
+    def transfer_async(self, job_id: int, spec: TransferSpec) -> bool:
+        src, dst = spec
+        assert isinstance(src, LoadStoreSpec2)
+        assert isinstance(dst, LoadStoreSpec1)
+
+        self.transfers[job_id] = dst
+        return True
+
+    def get_finished(self) -> list[TransferResult]:
+        finished = []
+        for job_id, spec in list(self.transfers.items()):
+            if spec.finished:
+                finished.append((job_id, spec.async_success))
+                del self.transfers[job_id]
+        return finished
+
+
+def test_offloading_worker():
+    """
+    Tests OffloadingWorker with 2 handlers.
+    One handler performs 1->2 transfers, and the other handles 2->1.
+    """
+    worker = OffloadingWorker()
+    handler1to2 = OffloadingHandler1To2()
+    handler2to1 = OffloadingHandler2To1()
+    worker.register_handler(LoadStoreSpec1, LoadStoreSpec2, handler1to2)
+    worker.register_handler(LoadStoreSpec2, LoadStoreSpec1, handler2to1)
+
+    # 1st transfer 1->2 (exception)
+    src1 = LoadStoreSpec1(exception=True)
+    dst1 = LoadStoreSpec2()
+    assert not worker.transfer_async(1, (src1, dst1))
+
+    # 2ed transfer 1->2 (failure to submit)
+    src2 = LoadStoreSpec1(submit_success=False)
+    dst2 = LoadStoreSpec2()
+    assert not worker.transfer_async(2, (src2, dst2))
+
+    # 3rd transfer 1->2 (failure)
+    src3 = LoadStoreSpec1(async_success=False)
+    dst3 = LoadStoreSpec2()
+    assert worker.transfer_async(3, (src3, dst3))
+
+    # 4th transfer 1->2 (success)
+    src4 = LoadStoreSpec1()
+    dst4 = LoadStoreSpec2()
+    worker.transfer_async(4, (src4, dst4))
+    assert set(handler1to2.transfers.keys()) == {3, 4}
+
+    # 5th transfer 2->1
+    src5 = LoadStoreSpec2()
+    dst5 = LoadStoreSpec1()
+    worker.transfer_async(5, (src5, dst5))
+    assert set(handler2to1.transfers.keys()) == {5}
+
+    # no transfer completed yet
+    assert worker.get_finished() == []
+
+    # complete 3rd, 4th
+    src3.finished = True
+    src4.finished = True
+
+    # 6th transfer 1->2
+    src6 = LoadStoreSpec1()
+    dst6 = LoadStoreSpec2()
+    worker.transfer_async(6, (src6, dst6))
+
+    # 7th transfer 2->1
+    src7 = LoadStoreSpec2()
+    dst7 = LoadStoreSpec1()
+    worker.transfer_async(7, (src7, dst7))
+
+    # 6th and 7th transfers started
+    assert 6 in handler1to2.transfers
+    assert 7 in handler2to1.transfers
+
+    # verify result of 3rd and 4th transfers
+    assert (sorted(worker.get_finished()) == [(3, False), (4, True)])
+
+    # complete 6th and 7th transfers
+    src6.finished = True
+    dst7.finished = True
+    assert (sorted(worker.get_finished()) == [(6, True), (7, True)])

vllm/v1/offloading/abstract.py

@@ -0,0 +1,165 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""
+OffloadingManager class for managing KV data offloading in vLLM v1
+
+This class runs in the scheduler, tracks which blocks are offloaded
+and their address.
+
+The class provides the following primitives:
+    lookup() - find the length of the maximal series of blocks,
+        starting from the first one, that are all offloaded.
+    prepare_load() - prepare given blocks to be read.
+        The given blocks will be protected from eviction.
+        This function returns a LoadSpec which encapsulates
+        information required for performing the load.
+    touch() - marks the give blocks as recently used. Can be used
+        to track block's LRU. This function is separated from the
+        prepare_load function to allow setting block recency even
+        for blocks which do not need reading from the cache, such as
+        blocks that are cached by the GPU prefix cache.
+    complete_load() - mark blocks which were previously prepared to be
+        loaded as done loading. This is to re-allow their eviction.
+    prepare_store() - prepare the given blocks to be written.
+        Returns a StoreSpec encapsulating offloading information,
+        as well as a list of blocks that were evicted as a result.
+    complete_store() - marks a previous store as completed.
+        Following this call, the given blocks will become loadable.
+"""
+
+from abc import ABC, abstractmethod
+from collections.abc import Iterable
+from dataclasses import dataclass
+from typing import Optional
+
+from vllm.v1.core.kv_cache_utils import BlockHash
+
+
+class LoadStoreSpec(ABC):
+    """
+    Abstract metadata that encapsulates information allowing a worker
+    to load, and optionally also to store, blocks of KV data.
+    """
+
+    @staticmethod
+    @abstractmethod
+    def medium() -> str:
+        """
+        Returns a string representation of the medium type
+        this store/load targets.
+        """
+        pass
+
+
+@dataclass
+class PrepareStoreOutput:
+    block_hashes_to_store: list[BlockHash]
+    store_spec: LoadStoreSpec
+    block_hashes_evicted: list[BlockHash]
+
+
+@dataclass
+class OffloadingEvent:
+    block_hashes: list[BlockHash]
+    block_size: int
+    medium: str
+    # True if blocks are removed, False if stored
+    removed: bool
+
+
+class OffloadingManager(ABC):
+
+    @abstractmethod
+    def lookup(self, block_hashes: Iterable[BlockHash]) -> int:
+        """
+        Finds the length of the maximal series of blocks, starting from the
+        first one, that are all offloaded.
+
+        Args:
+            block_hashes: the hashes identifying the blocks to lookup.
+
+        Returns:
+            An integer representing the maximal number of blocks that
+            are currently offloaded.
+        """
+        pass
+
+    @abstractmethod
+    def prepare_load(self, block_hashes: Iterable[BlockHash]) -> LoadStoreSpec:
+        """
+        Prepare the given blocks to be read.
+        The given blocks will be protected from eviction until
+        complete_load is called.
+        It assumes all given blocks are offloaded.
+
+        Args:
+            block_hashes: the hashes identifying the blocks.
+
+        Returns:
+            A LoadStoreSpec that can be used by a worker to locate and load
+            the actual offloaded KV data.
+        """
+        pass
+
+    def touch(self, block_hashes: Iterable[BlockHash]):
+        """
+        Mark the given blocks as recently used.
+        This could in practice mean moving them to the end of an LRU list.
+
+        Args:
+            block_hashes: the hashes identifying the blocks.
+        """
+        return
+
+    def complete_load(self, block_hashes: Iterable[BlockHash]):
+        """
+        Marks previous blocks that were prepared to load as done loading.
+
+        Args:
+            block_hashes: the hashes identifying the blocks.
+        """
+        return
+
+    @abstractmethod
+    def prepare_store(
+            self,
+            block_hashes: Iterable[BlockHash]) -> Optional[PrepareStoreOutput]:
+        """
+        Prepare the given blocks to be offloaded.
+        The given blocks will be protected from eviction until
+        complete_store is called.
+
+        Args:
+            block_hashes: the hashes identifying the blocks.
+
+        Returns:
+            A PrepareStoreOutput indicating which blocks need storing,
+            where to store them (LoadStoreSpec), and list of blocks that
+            were evicted as a result.
+            None is returned if the blocks cannot be stored.
+        """
+        pass
+
+    def complete_store(self,
+                       block_hashes: Iterable[BlockHash],
+                       success: bool = True):
+        """
+        Marks blocks which were previously prepared to be stored, as stored.
+        Following this call, the blocks become loadable.
+        If if_success is False, blocks that were not marked as stored will be
+        removed.
+
+        Args:
+            block_hashes: the hashes identifying the blocks.
+            success: whether the blocks were stored successfully.
+        """
+        return
+
+    def take_events(self) -> Iterable[OffloadingEvent]:
+        """
+        Take the offloading events from the manager.
+
+        Yields:
+            New OffloadingEvents collected since the last call.
+        """
+        return ()

vllm/v1/offloading/mediums.py

@@ -0,0 +1,39 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+from abc import ABC
+
+import numpy as np
+
+from vllm.v1.offloading.abstract import LoadStoreSpec
+
+
+class BlockIDsLoadStoreSpec(LoadStoreSpec, ABC):
+    """
+    Spec for loading/storing KV blocks from given block numbers.
+    """
+
+    def __init__(self, block_ids: list[int]):
+        self.block_ids = np.array(block_ids, dtype=np.int64)
+
+    def __repr__(self) -> str:
+        return repr(self.block_ids)
+
+
+class GPULoadStoreSpec(BlockIDsLoadStoreSpec):
+    """
+    Spec for loading/storing a KV block to GPU memory.
+    """
+
+    @staticmethod
+    def medium() -> str:
+        return "GPU"
+
+
+class CPULoadStoreSpec(BlockIDsLoadStoreSpec):
+    """
+    Spec for loading/storing a KV block to CPU memory.
+    """
+
+    @staticmethod
+    def medium() -> str:
+        return "CPU"