250 lines
9.8 KiB
Python
250 lines
9.8 KiB
Python
from typing import Dict, List, Optional, Set, Tuple
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from cacheflow.block import PhysicalTokenBlock
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from cacheflow.sequence import Sequence
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from cacheflow.sequence import SequenceGroup
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from cacheflow.sequence import SequenceStatus
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from cacheflow.utils import Device
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class BlockAllocator:
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def __init__(
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self,
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device: Device,
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block_size: int,
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num_blocks: int,
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) -> None:
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if block_size not in [8, 16, 32]:
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raise ValueError(f'Unsupported block size: {block_size}'
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'The block size must be one of {8, 16, 32}.')
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self.device = device
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self.block_size = block_size
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self.num_blocks = num_blocks
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# Initialize the free blocks.
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# TODO(woosuk): Make this a priority queue.
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self.free_blocks = [
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PhysicalTokenBlock(device=device, block_number=i, block_size=block_size)
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for i in range(num_blocks)
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]
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def allocate(self) -> PhysicalTokenBlock:
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if not self.free_blocks:
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raise ValueError('Out of memory! '
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f'No more free blocks are available.')
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block = self.free_blocks.pop()
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block.ref_count = 1
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return block
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def free(self, block: PhysicalTokenBlock) -> None:
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if block.ref_count == 0:
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raise ValueError('Double free! '
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f'The block {block} is already freed.')
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block.ref_count -= 1
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if block.ref_count == 0:
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self.free_blocks.append(block)
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def get_num_free_blocks(self) -> int:
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return len(self.free_blocks)
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# Mapping: logical block number -> physical block.
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BlockTable = List[PhysicalTokenBlock]
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class BlockSpaceManager:
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def __init__(
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self,
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block_size: int,
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num_gpu_blocks: int,
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num_cpu_blocks: int,
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watermark: float = 0.01,
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) -> None:
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self.block_size = block_size
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self.num_total_gpu_blocks = num_gpu_blocks
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self.num_total_cpu_blocks = num_cpu_blocks
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self.watermark = watermark
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assert watermark >= 0.0
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self.watermark_blocks = int(watermark * num_gpu_blocks)
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self.gpu_allocator = BlockAllocator(Device.GPU, block_size, num_gpu_blocks)
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self.cpu_allocator = BlockAllocator(Device.CPU, block_size, num_cpu_blocks)
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# Mapping: seq_id -> BlockTable.
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self.block_tables: Dict[int, BlockTable] = {}
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def can_allocate(self, seq_group: SequenceGroup) -> bool:
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# FIXME(woosuk): Here we assume that all sequences in the group share
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# the same prompt. This may not be true for preempted sequences.
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seq = seq_group.seqs[0]
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num_required_blocks = len(seq.logical_token_blocks)
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num_free_gpu_blocks = self.gpu_allocator.get_num_free_blocks()
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# Use watermark to avoid frequent cache eviction.
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return num_free_gpu_blocks - num_required_blocks >= self.watermark_blocks
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def allocate(self, seq_group: SequenceGroup) -> None:
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# NOTE: Here we assume that all sequences in the group have the same prompt.
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seq = seq_group.seqs[0]
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# Allocate new physical token blocks that will store the prompt tokens.
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block_table: BlockTable = []
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for _ in range(len(seq.logical_token_blocks)):
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block = self.gpu_allocator.allocate()
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# Set the reference counts of the token blocks.
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block.ref_count = seq_group.num_seqs()
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block_table.append(block)
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# Assign the block table for each sequence.
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for seq in seq_group.seqs:
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self.block_tables[seq.seq_id] = block_table.copy()
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def can_append(self, seq_group: SequenceGroup) -> bool:
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# Simple heuristic: If there is at least one free block
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# for each sequence, we can append.
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num_free_gpu_blocks = self.gpu_allocator.get_num_free_blocks()
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num_seqs = seq_group.num_seqs(status=SequenceStatus.RUNNING)
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return num_seqs <= num_free_gpu_blocks
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def append(self, seq: Sequence) -> Optional[Tuple[int, int]]:
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"""Allocate a physical slot for the new token."""
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logical_blocks = seq.logical_token_blocks
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block_table = self.block_tables[seq.seq_id]
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if len(block_table) < len(logical_blocks):
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# The sequence has a new logical block.
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# Allocate a new physical block.
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block = self.gpu_allocator.allocate()
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block_table.append(block)
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return None
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# We want to append the token to the last physical block.
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last_block = block_table[-1]
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assert last_block.device == Device.GPU
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if last_block.ref_count == 1:
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# Not shared with other sequences. Appendable.
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return None
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else:
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# The last block is shared with other sequences.
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# Copy on Write: Allocate a new block and copy the tokens.
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new_block = self.gpu_allocator.allocate()
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block_table[-1] = new_block
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self.gpu_allocator.free(last_block)
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return last_block.block_number, new_block.block_number
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def fork(self, parent_seq: Sequence, child_seq: Sequence) -> None:
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# NOTE: fork does not allocate a new physical block.
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# Thus, it is always safe from OOM.
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src_block_table = self.block_tables[parent_seq.seq_id]
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self.block_tables[child_seq.seq_id] = src_block_table.copy()
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for block in src_block_table:
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block.ref_count += 1
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def _get_physical_blocks(self, seq_group: SequenceGroup) -> List[PhysicalTokenBlock]:
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# NOTE: Here, we assume that the physical blocks are only shared by
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# the sequences in the same group.
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blocks: Set[PhysicalTokenBlock] = set()
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for seq in seq_group.seqs:
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if seq.status == SequenceStatus.FINISHED:
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continue
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block_table = self.block_tables[seq.seq_id]
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for block in block_table:
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blocks.add(block)
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return list(blocks)
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def can_swap_in(self, seq_group: SequenceGroup) -> bool:
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blocks = self._get_physical_blocks(seq_group)
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num_swapped_seqs = seq_group.num_seqs(status=SequenceStatus.SWAPPED)
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num_free_blocks = self.gpu_allocator.get_num_free_blocks()
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# NOTE: Conservatively, we assume that every sequence will allocate
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# at least one free block right after the swap-in.
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# NOTE: This should match the logic in can_append().
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num_required_blocks = len(blocks) + num_swapped_seqs
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return num_free_blocks - num_required_blocks >= self.watermark_blocks
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def swap_in(self, seq_group: SequenceGroup) -> Dict[int, int]:
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# CPU block -> GPU block.
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mapping: Dict[PhysicalTokenBlock, PhysicalTokenBlock] = {}
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for seq in seq_group.seqs:
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if seq.status == SequenceStatus.FINISHED:
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continue
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new_block_table: BlockTable = []
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block_table = self.block_tables[seq.seq_id]
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for cpu_block in block_table:
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if cpu_block in mapping:
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gpu_block = mapping[cpu_block]
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gpu_block.ref_count += 1
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else:
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gpu_block = self.gpu_allocator.allocate()
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mapping[cpu_block] = gpu_block
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new_block_table.append(gpu_block)
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# Free the CPU block swapped in to GPU.
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self.cpu_allocator.free(cpu_block)
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self.block_tables[seq.seq_id] = new_block_table
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block_number_mapping = {
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cpu_block.block_number: gpu_block.block_number
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for cpu_block, gpu_block in mapping.items()
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}
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return block_number_mapping
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def can_swap_out(self, seq_group: SequenceGroup) -> bool:
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blocks = self._get_physical_blocks(seq_group)
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return len(blocks) <= self.cpu_allocator.get_num_free_blocks()
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def swap_out(self, seq_group: SequenceGroup) -> Dict[int, int]:
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# GPU block -> CPU block.
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mapping: Dict[PhysicalTokenBlock, PhysicalTokenBlock] = {}
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for seq in seq_group.seqs:
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if seq.status == SequenceStatus.FINISHED:
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continue
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new_block_table: BlockTable = []
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block_table = self.block_tables[seq.seq_id]
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for gpu_block in block_table:
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if gpu_block in mapping:
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cpu_block = mapping[gpu_block]
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cpu_block.ref_count += 1
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else:
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cpu_block = self.cpu_allocator.allocate()
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mapping[gpu_block] = cpu_block
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new_block_table.append(cpu_block)
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# Free the GPU block swapped out to CPU.
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self.gpu_allocator.free(gpu_block)
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self.block_tables[seq.seq_id] = new_block_table
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block_number_mapping = {
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gpu_block.block_number: cpu_block.block_number
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for gpu_block, cpu_block in mapping.items()
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}
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return block_number_mapping
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def _free_block_table(self, block_table: BlockTable) -> None:
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for block in block_table:
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if block.device == Device.GPU:
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self.gpu_allocator.free(block)
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else:
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self.cpu_allocator.free(block)
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def free(self, seq: Sequence) -> None:
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block_table = self.block_tables[seq.seq_id]
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self._free_block_table(block_table)
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del self.block_tables[seq.seq_id]
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def reset(self) -> None:
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for block_table in self.block_tables.values():
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self._free_block_table(block_table)
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self.block_tables.clear()
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def get_block_table(self, seq: Sequence) -> List[int]:
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block_table = self.block_tables[seq.seq_id]
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return [block.block_number for block in block_table]
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def get_num_free_gpu_blocks(self) -> int:
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return self.gpu_allocator.get_num_free_blocks()
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def get_num_free_cpu_blocks(self) -> int:
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return self.cpu_allocator.get_num_free_blocks()
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