369 lines
12 KiB
Python
369 lines
12 KiB
Python
import threading
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from collections import OrderedDict
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from typing import Callable, Dict, List, Optional, Tuple
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import torch
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from torch import Tensor
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def page_hash(token_ids: List[int], page_idx: int, page_size: int) -> int:
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start = page_idx * page_size
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end = min(start + page_size, len(token_ids))
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h = 0
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for i in range(start, end):
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h = (h * 31 + token_ids[i]) & 0xFFFFFFFFFFFFFFFF
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return h
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class Allocator:
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"""Bitmask-based page allocator with ref-counting and LRU eviction."""
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def __init__(self, n_pages: int):
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self._free_mask = (1 << n_pages) - 1
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self._refs: List[int] = [0] * n_pages
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self._lru: OrderedDict[int, None] = OrderedDict()
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self.on_evict: Optional[Callable[[int], None]] = None
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self._lock = threading.Lock()
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def alloc(self) -> int:
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with self._lock:
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if self._free_mask:
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lsb = self._free_mask & -self._free_mask
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idx = lsb.bit_length() - 1
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self._free_mask ^= lsb
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self._refs[idx] = 1
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return idx
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if self._lru:
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idx, _ = self._lru.popitem(last=False)
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if self.on_evict:
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self.on_evict(idx)
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self._refs[idx] = 1
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self._free_mask &= ~(1 << idx)
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return idx
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return -1
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def free(self, idx: int, keep_cached: bool = False):
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with self._lock:
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self._refs[idx] -= 1
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if self._refs[idx] == 0:
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if keep_cached:
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self._lru[idx] = None
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else:
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self._free_mask |= 1 << idx
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def inc_ref(self, idx: int):
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with self._lock:
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self._refs[idx] += 1
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self._lru.pop(idx, None)
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def ref_count(self, idx: int) -> int:
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with self._lock:
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return self._refs[idx]
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def touch(self, idx: int):
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with self._lock:
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self._lru.move_to_end(idx)
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class PrefixCache:
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"""Hash-based prefix matching: maps page hashes to physical page indices."""
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def __init__(self, page_size: int):
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self._page_size = page_size
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self._page_to_hash: Dict[int, int] = {}
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self._hash_to_page: Dict[int, int] = {}
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self._lock = threading.Lock()
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def evict(self, idx: int):
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with self._lock:
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h = self._page_to_hash.pop(idx, None)
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if h is not None:
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self._hash_to_page.pop(h, None)
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def has_page(self, idx: int) -> bool:
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with self._lock:
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return idx in self._page_to_hash
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def lookup(self, token_ids: List[int]) -> List[int]:
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with self._lock:
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full_pages = len(token_ids) // self._page_size
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hits: List[int] = []
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for i in range(full_pages):
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h = page_hash(token_ids, i, self._page_size)
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p = self._hash_to_page.get(h)
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if p is None:
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break
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hits.append(p)
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return hits
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def record(self, page_idx: int, token_ids: List[int], logical_page_idx: int):
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with self._lock:
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h = page_hash(token_ids, logical_page_idx, self._page_size)
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old_h = self._page_to_hash.pop(page_idx, None)
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if old_h is not None:
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self._hash_to_page.pop(old_h, None)
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self._page_to_hash[page_idx] = h
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self._hash_to_page[h] = page_idx
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class PagePool:
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"""Orchestrates allocator (page management) and PrefixCache (content addressing)."""
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def __init__(self, allocator: Allocator, prefix: PrefixCache):
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self._alloc = allocator
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self._prefix = prefix
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self._alloc.on_evict = prefix.evict
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@property
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def allocator(self) -> Allocator:
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return self._alloc
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@property
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def prefix(self) -> PrefixCache:
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return self._prefix
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def alloc(self) -> int:
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return self._alloc.alloc()
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def free(self, idx: int):
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keep = self._prefix.has_page(idx)
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self._alloc.free(idx, keep_cached=keep)
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if not keep:
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self._prefix.evict(idx)
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def inc_ref(self, idx: int):
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self._alloc.inc_ref(idx)
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def lookup(self, token_ids: List[int]) -> List[int]:
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hits = self._prefix.lookup(token_ids)
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for p in hits:
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self._alloc.touch(p)
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return hits
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def record(self, page_idx: int, token_ids: List[int], logical_page_idx: int):
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self._prefix.record(page_idx, token_ids, logical_page_idx)
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class TaskTable:
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"""Maps task_ids to page tables and cached token counts."""
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def __init__(self, page_size: int):
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self._page_size = page_size
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self._pages: Dict[str, List[int]] = {}
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self._cached: Dict[str, int] = {}
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self._lock = threading.Lock()
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def set(self, task_id: str, page_table: List[int], cached: int):
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with self._lock:
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self._pages[task_id] = page_table
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self._cached[task_id] = cached
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def get(self, task_id: str) -> List[int]:
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with self._lock:
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return self._pages.get(task_id, [])
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def get_cached(self, task_id: str) -> int:
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with self._lock:
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return self._cached.get(task_id, 0)
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def pop(self, task_id: str) -> Tuple[List[int], int]:
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with self._lock:
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pages = self._pages.pop(task_id, [])
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cached = self._cached.pop(task_id, 0)
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return pages, cached
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def get_ref(self, task_id: str) -> List[int]:
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with self._lock:
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return self._pages.setdefault(task_id, [])
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def table_tensor(self, task_ids: List[str], device: torch.device) -> Tensor:
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with self._lock:
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states = [self._pages.get(tid, []) for tid in task_ids]
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max_pages = max((len(s) for s in states), default=0)
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rows = [s + [-1] * (max_pages - len(s)) for s in states]
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return torch.tensor(rows, dtype=torch.long, device=device)
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class Storage:
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"""KV-cache tensor storage with paged write/gather."""
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def __init__(
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self,
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n_layers: int,
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n_pages: int,
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page_size: int,
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n_kv_heads: int,
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head_dim: int,
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device: torch.device,
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dtype: torch.dtype,
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):
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self.page_size = page_size
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self.k_cache = torch.empty(
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(n_layers, n_pages, page_size, n_kv_heads, head_dim),
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device=device,
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dtype=dtype,
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)
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self.v_cache = torch.empty(
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(n_layers, n_pages, page_size, n_kv_heads, head_dim),
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device=device,
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dtype=dtype,
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)
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def write(
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self,
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layer_id: int,
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page_table: Tensor,
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start_pos: int,
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k: Tensor,
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v: Tensor,
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):
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seq_len = k.size(1)
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if seq_len == 0:
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return
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page_size = self.page_size
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written = 0
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first_page = start_pos // page_size
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last_page = (start_pos + seq_len - 1) // page_size
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for pi in range(first_page, last_page + 1):
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phys_pages = page_table[:, pi]
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page_start = pi * page_size
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write_start = max(page_start, start_pos)
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write_end = min(page_start + page_size, start_pos + seq_len)
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offset = write_start - page_start
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chunk = write_end - write_start
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valid = phys_pages >= 0
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if not valid.all():
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if valid.any():
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valid_pages = phys_pages[valid]
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self.k_cache[layer_id, valid_pages, offset : offset + chunk] = k[
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valid, written : written + chunk
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]
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self.v_cache[layer_id, valid_pages, offset : offset + chunk] = v[
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valid, written : written + chunk
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]
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written += chunk
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continue
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self.k_cache[layer_id, phys_pages, offset : offset + chunk] = k[
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:, written : written + chunk
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]
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self.v_cache[layer_id, phys_pages, offset : offset + chunk] = v[
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:, written : written + chunk
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]
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written += chunk
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def gather(
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self, layer_id: int, page_table: Tensor, total_len: int
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) -> Tuple[Tensor, Tensor]:
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safe = page_table.clamp(min=0)
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k = self.k_cache[layer_id, safe]
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v = self.v_cache[layer_id, safe]
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k = k.flatten(1, 2)
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v = v.flatten(1, 2)
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if (page_table < 0).any():
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invalid = (
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(page_table < 0)
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.unsqueeze(-1)
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.expand(-1, -1, self.page_size)
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.flatten(1, 2)
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)
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invalid = invalid[:, :, None, None].expand_as(k)
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k = k.masked_fill(invalid, 0.0)
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v = v.masked_fill(invalid, 0.0)
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k = k[:, :total_len]
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v = v[:, :total_len]
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return k, v
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class KvcacheView:
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"""Bundles Storage + page_table + total_len for attention layers."""
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def __init__(self, storage: Storage, page_table: Tensor, total_len: int = 0):
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self._storage = storage
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self._page_table = page_table
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self._total_len = total_len
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def write(self, layer_id: int, k: Tensor, v: Tensor):
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start_pos = self._total_len - k.size(1)
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self._storage.write(layer_id, self._page_table, start_pos, k, v)
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def gather(self, layer_id: int) -> Tuple[Tensor, Tensor]:
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return self._storage.gather(layer_id, self._page_table, self._total_len)
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class KVCache:
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"""Facade: page management + KV-cache I/O for continuous batching."""
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def __init__(
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self,
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n_layers: int,
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n_pages: int,
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page_size: int,
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n_kv_heads: int,
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head_dim: int,
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device: torch.device,
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dtype: torch.dtype,
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):
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self.page_size = page_size
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self._pool = PagePool(Allocator(n_pages), PrefixCache(page_size))
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self._table = TaskTable(page_size)
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self._storage = Storage(
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n_layers, n_pages, page_size, n_kv_heads, head_dim, device, dtype
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)
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def task_alloc(self, task_id: str, prompt_ids: List[int]) -> bool:
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hits = self._pool.lookup(prompt_ids)
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cached = len(hits) * self.page_size
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for p in hits:
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self._pool.inc_ref(p)
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remaining = len(prompt_ids) - cached
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n_new = (
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(remaining + self.page_size - 1) // self.page_size if remaining > 0 else 0
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)
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new_pages: List[int] = []
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if n_new > 0:
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for _ in range(n_new):
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p = self._pool.alloc()
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if p < 0:
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for hp in hits:
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self._pool.free(hp)
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for np in new_pages:
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self._pool.free(np)
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return False
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new_pages.append(p)
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self._table.set(task_id, hits + new_pages, cached)
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return True
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def task_free(self, task_id: str):
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page_table, _ = self._table.pop(task_id)
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for idx in page_table:
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self._pool.free(idx)
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def task_extend(self, task_id: str, pos: int) -> bool:
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page_table = self._table.get(task_id)
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needed = (pos + 1 + self.page_size - 1) // self.page_size
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while len(page_table) < needed:
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p = self._pool.alloc()
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if p < 0:
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return False
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page_table.append(p)
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return True
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def task_cached(self, task_id: str) -> int:
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return self._table.get_cached(task_id)
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def task_record_hashes(
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self, task_id: str, prompt_ids: List[int], start_logical_page: int = 0
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):
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page_table = self._table.get(task_id)
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full_pages = len(prompt_ids) // self.page_size
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for i in range(start_logical_page, full_pages):
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self._pool.record(page_table[i], prompt_ids, i)
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def make_table_tensor(self, task_ids: List[str], device: torch.device) -> Tensor:
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return self._table.table_tensor(task_ids, device)
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def bind(self, page_table: Tensor, total_len: int = 0) -> KvcacheView:
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return KvcacheView(self._storage, page_table, total_len)
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