Add block manager

cacheflow/master/block_manager.py

+from typing import Dict, Iterable, List, Optional, Set, Tuple
+
+from cacheflow.block import PhysicalTokenBlock
+from cacheflow.sequence import Sequence
+from cacheflow.sequence import SequenceGroup
+from cacheflow.sequence import SequenceStatus
+from cacheflow.utils import Device
+
+
+class BlockAllocator:
+
+    def __init__(
+        self,
+        device: Device,
+        block_size: int,
+        num_blocks: int,
+    ) -> None:
+        assert block_size in [8, 16, 32]
+        self.device = device
+        self.block_size = block_size
+        self.num_blocks = num_blocks
+
+        # Initialize the free blocks.
+        # TODO(woosuk): Make this a priority queue.
+        self.free_blocks = [
+            PhysicalTokenBlock(device=device, block_number=i, block_size=block_size)
+            for i in range(num_blocks)
+        ]
+
+    def allocate(self) -> PhysicalTokenBlock:
+        if not self.free_blocks:
+            raise ValueError('Out of memory! '
+                             f'No more free blocks are available.')
+        block = self.free_blocks.pop()
+        block.ref_count = 1
+        return block
+
+    def free(self, block: PhysicalTokenBlock) -> None:
+        if block.ref_count == 0:
+            raise ValueError('Double free! '
+                             f'The block {block} is already freed.')
+        block.ref_count -= 1
+        if block.ref_count == 0:
+            self.free_blocks.append(block)
+
+    def get_num_free_blocks(self) -> int:
+        return len(self.free_blocks)
+
+
+# Mapping: logical block number -> physical block.
+BlockTable = List[PhysicalTokenBlock]
+
+
+class BlockSpaceManager:
+
+    def __init__(
+        self,
+        block_size: int,
+        num_gpu_blocks: int,
+        num_cpu_blocks: int,
+    ) -> None:
+        self.block_size = block_size
+        self.num_total_gpu_blocks = num_gpu_blocks
+        self.num_total_cpu_blocks = num_cpu_blocks
+
+        self.gpu_allocator = BlockAllocator(Device.GPU, block_size, num_gpu_blocks)
+        self.cpu_allocator = BlockAllocator(Device.CPU, block_size, num_cpu_blocks)
+
+        # Mapping: seq_id -> BlockTable.
+        self.block_tables: Dict[int, BlockTable] = {}
+
+    def can_allocate(self, seq_group: SequenceGroup) -> bool:
+        seq = seq_group.seqs[0]
+        num_required_blocks = len(seq.logical_token_blocks)
+        num_free_gpu_blocks = self.gpu_allocator.get_num_free_blocks()
+        return num_required_blocks <= num_free_gpu_blocks
+
+    def allocate(self, seq_group: SequenceGroup) -> None:
+        # Here, we assume that all sequences in the group have the same prompt.
+        seq = seq_group.seqs[0]
+
+        # Allocate new physical token blocks that will store the prompt tokens.
+        block_table: BlockTable = []
+        for _ in range(len(seq.logical_token_blocks)):
+            block = self.gpu_allocator.allocate()
+            # Set the reference counts of the token blocks.
+            block.ref_count = seq_group.num_seqs()
+            block_table.append(block)
+
+        # Assign the block table for each sequence.
+        for seq in seq_group.seqs:
+            self.block_tables[seq.seq_id] = block_table.copy()
+
+    def can_append(self, seq_group: SequenceGroup) -> bool:
+        # Simple heuristic: If there is at least one free block
+        # for each sequence, we can append.
+        num_free_gpu_blocks = self.gpu_allocator.get_num_free_blocks()
+        num_seqs = seq_group.num_seqs(status=SequenceStatus.SERVING)
+        return num_seqs <= num_free_gpu_blocks
+
+    def append(self, seq: Sequence) -> Optional[Tuple[int, int]]:
+        """Allocate a physical slot for the new token."""
+        logical_blocks = seq.logical_token_blocks
+        block_table = self.block_tables[seq.seq_id]
+
+        if len(block_table) < len(logical_blocks):
+            # The sequence has a new logical block.
+            # Allocate a new physical block.
+            block = self.gpu_allocator.allocate()
+            block_table.append(block)
+            return None
+
+        # We want to append the token to the last physical block.
+        last_block = block_table[-1]
+        assert last_block.device == Device.GPU
+        if last_block.ref_count == 1:
+            # Append.
+            return None
+        else:
+            # The last block is shared with other sequences.
+            # Copy on Write: Allocate a new block and copy the tokens.
+            block = self.gpu_allocator.allocate()
+            block_table.append(block)
+            self.gpu_allocator.free(last_block)
+            return last_block.block_number, block.block_number
+
+    def fork(self, src_seq: Sequence, child_seq: Sequence) -> None:
+        # NOTE: fork does not allocate a new physical block.
+        # Thus, it is always safe from OOM.
+        src_block_table = self.block_tables[src_seq.seq_id]
+        self.block_tables[child_seq.seq_id] = src_block_table.copy()
+        for block in src_block_table:
+            block.ref_count += 1
+
+    def _get_physical_blocks(self, seq_group: SequenceGroup) -> List[PhysicalTokenBlock]:
+        # NOTE: Here, we assume that the physical blocks are only shared by
+        # the sequences in the same group.
+        blocks: Set[PhysicalTokenBlock] = set()
+        for seq in seq_group.seqs:
+            if seq.status == SequenceStatus.FINISHED:
+                continue
+            block_table = self.block_tables[seq.seq_id]
+            for block in block_table:
+                blocks.add(block)
+        return list(blocks)
+
+    def can_swap_in(self, seq_group: SequenceGroup) -> bool:
+        blocks = self._get_physical_blocks(seq_group)
+        return len(blocks) <= self.gpu_allocator.get_num_free_blocks()
+
+    def swap_in(self, seq_group: SequenceGroup) -> Dict[int, int]:
+        # src_block_number -> dst_block_number
+        mapping: Dict[int, int] = {}
+        for seq in seq_group.seqs:
+            if seq.status == SequenceStatus.FINISHED:
+                continue
+            block_table = self.block_tables[seq.seq_id]
+
+            for cpu_block in block_table:
+                if cpu_block in mapping:
+                    continue
+                gpu_block = self.gpu_allocator.allocate()
+                mapping[cpu_block.block_number] = gpu_block.block_number
+                # Free the CPU block swapped in to GPU.
+                self.cpu_allocator.free(cpu_block)
+        return mapping
+
+    def can_swap_out(self, seq_group: SequenceGroup) -> bool:
+        blocks = self._get_physical_blocks(seq_group)
+        return len(blocks) <= self.cpu_allocator.get_num_free_blocks()
+
+    def swap_out(self, seq_group: SequenceGroup) -> Dict[int, int]:
+        # src_block_number -> dst_block_number
+        mapping: Dict[int, int] = {}
+        for seq in seq_group.seqs:
+            if seq.status == SequenceStatus.FINISHED:
+                continue
+            block_table = self.block_tables[seq.seq_id]
+
+            for gpu_block in block_table:
+                if gpu_block.block_number in mapping:
+                    continue
+                cpu_block = self.cpu_allocator.allocate()
+                mapping[gpu_block.block_number] = cpu_block.block_number
+                # Free the GPU block swapped out to CPU.
+                self.gpu_allocator.free(gpu_block)
+        return mapping
+
+    def _free_blocks(self, blocks: Iterable[PhysicalTokenBlock]) -> None:
+        for block in blocks:
+            if block.device == Device.GPU:
+                self.gpu_allocator.free(block)
+            else:
+                self.cpu_allocator.free(block)
+
+    def free(self, seq: Sequence) -> None:
+        block_table = self.block_tables[seq.seq_id]
+        self._free_blocks(block_table)
+        del self.block_tables[seq.seq_id]
+
+    def reset(self) -> None:
+        for block_table in self.block_tables.values():
+            self._free_blocks(block_table)
+        self.block_tables.clear()