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vLLM-4x-RTX-3090/patches/0093-mamba-hold-the-partial-tail-CoW-checkpoint-until-the.patch
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MOVZX 777e910dd0 Initial commit 
Signed-off-by: MOVZX <movzx@yahoo.com>
2026-10-15 01:01:52 +07:00

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From 2c86f0cf169ab1274238260bca55a7dabfffd7d0 Mon Sep 17 00:00:00 2001
From: halt95 <halt95@users.noreply.github.com>
Date: Tue, 6 Oct 2026 02:49:51 -0400
Subject: [PATCH 093/103] mamba: hold the partial-tail CoW checkpoint until the
request is freed
With --prefix-match-unit below the block size, a follow-up turn that
resumes at a partial tail (mid-block) never hashes a block-boundary GDN
state. Under retention interval 0 the only boundary kept is the replay
boundary, which lies below the resume point. The request's own tail is
published on its running block and moved into a CoW block by the next
chunk, and the scheduler releases both copy endpoints once the copy has
run. That block then sat at ref 0 in the free queue for the rest of the
request, ahead of its attention blocks, and concurrent prefills popped
it. The hybrid hit is the shortest group's, so the next turn resumed at
0. Under a long-context multi-turn agent load, 7 of 61 follow-ups at
unit 64 (6 at 256/512/1024) came back with cached_tokens 0 on 80-100K
prompts whose whole attention prefix was still cached. Every one
followed a partial-tail resume, none followed a block-aligned one, and
unit 4096 never missed.
The existing retention (VLLM_E2_MAMBA_RETAIN_CHECKPOINT) only held
hashed blocks retired from the table, so it never covered that copy.
Now, under the same switch:
- The running-request CoW branch holds the moved tail block in
_retained_checkpoints with a ref of its own; the copy retention pair
is unchanged. The new-request branch holds the hit source after
_apply_cow for the same reason: a request that stops before its own
tail still leaves the state it resumed from.
- _retained_checkpoints is keyed by block_hash_num_tokens instead of
block index, so a sub-block tail key orders correctly against full
block states; _retire_state_blocks uses the same key. The newest
position supersedes and releases the older one, so a request still
holds at most one block per group.
- When a producer moves its tail hashes into its CoW block, another
request holding that source (a sibling that resumed at the tail while
it was the producer's live block) follows the hashes to the copy.
- Admission reserves one extra block per Mamba group for a partial-tail
hit: the held source and the moved tail coexist at the tail step.
The hold is released on every free path (finish, abort, preemption,
deferred pop_blocks_for_free) by the coordinator, last, after the
request's attention blocks, as before. When the hold is active (switch
on, hash unit below the Mamba block) MambaManager logs one startup line
saying so, with the hash unit and block size.
Tests (CPU): a replay of the miss that fails on v2.5.0 with the
retention switch on (next-turn hit 0 instead of the tail) and passes
here; the structural variant; admission accounting; no-leak checks for
a request freed with its copy still queued, in both release orders; and
the moved-hash follow. The retention suite's one block-index assertion
now reads the token position.
---
.../test_partial_prefix_cache_hits.py | 499 ++++++++++++++++++
.../core/test_mamba_checkpoint_retention.py | 5 +-
vllm/v1/core/kv_cache_coordinator.py | 5 +-
vllm/v1/core/single_type_kv_cache_manager.py | 111 +++-
4 files changed, 606 insertions(+), 14 deletions(-)
diff --git a/tests/v1/core/prefix_cache/test_partial_prefix_cache_hits.py b/tests/v1/core/prefix_cache/test_partial_prefix_cache_hits.py
index 4798e0c..ee876b0 100644
--- a/tests/v1/core/prefix_cache/test_partial_prefix_cache_hits.py
+++ b/tests/v1/core/prefix_cache/test_partial_prefix_cache_hits.py
@@ -2532,3 +2532,502 @@ def test_boundary_states_offered_past_prompt_for_resumed_prefill():
offered = [b for _, _, b in drain_boundary_state_offloads(manager).get("0", [])]
assert 2 * block_size in offered
assert req0.num_prompt_tokens < 2 * block_size
+
+
+# ---------------------------------------------------------------------------
+# A partial-tail resume must leave its own tail checkpoint referenced
+# (the tail-CoW total miss, measured at --prefix-match-unit 64/256/512/1024).
+# ---------------------------------------------------------------------------
+TAIL_BLOCK = 32 # mamba block
+TAIL_HASH = 8 # prefix-match unit (full attention hashes at the unit)
+TAIL_SPEC = 3 # MTP K=3, as deployed
+TAIL_SWITCH = "VLLM_E2_MAMBA_RETAIN_CHECKPOINT"
+TAIL_ATTN = 0 # group ids
+TAIL_MAMBA = 1
+
+
+@pytest.fixture(params=["1", "0"], ids=["retain-on", "retain-off-control"])
+def tail_retain(request, monkeypatch) -> bool:
+ from vllm import envs
+
+ monkeypatch.setenv(TAIL_SWITCH, request.param)
+ if hasattr(envs.__getattr__, "cache_clear"):
+ envs.__getattr__.cache_clear()
+ return request.param == "1"
+
+
+def _tail_manager(num_blocks: int, use_eagle: bool = True):
+ """Full attention at the hash unit + one align-mode Mamba group at the
+ block, eagle/MTP drop on, retention interval 0 (the deployed default)."""
+ kv_cache_config = KVCacheConfig(
+ num_blocks=num_blocks,
+ kv_cache_tensors=[],
+ kv_cache_groups=[
+ KVCacheGroupSpec(
+ ["full"],
+ FullAttentionSpec(
+ block_size=TAIL_HASH,
+ num_kv_heads=1,
+ head_size=1,
+ dtype=torch.float32,
+ ),
+ ),
+ KVCacheGroupSpec(
+ ["mamba"],
+ MambaSpec(
+ block_size=TAIL_BLOCK,
+ shapes=(1, 1),
+ dtypes=(torch.float32,),
+ mamba_cache_mode="align",
+ num_speculative_blocks=TAIL_SPEC,
+ ),
+ ),
+ ],
+ )
+ manager = make_kv_cache_manager(
+ kv_cache_config=kv_cache_config,
+ max_model_len=8192,
+ enable_caching=True,
+ hash_block_size=TAIL_HASH,
+ use_eagle=use_eagle,
+ retention_interval=0,
+ )
+ assert manager.coordinator.enable_partial_hash_hits
+ return manager
+
+
+def _tail_split(
+ request, num_new: int, num_local_hit: int = 0, use_eagle: bool = True
+) -> int:
+ """The real ``Scheduler._mamba_block_aligned_split`` on a stub self."""
+ stub = SimpleNamespace(
+ block_size=TAIL_BLOCK,
+ cache_config=SimpleNamespace(block_size=TAIL_BLOCK),
+ use_eagle_block_drop=use_eagle,
+ max_num_scheduled_tokens=8192,
+ scheduler_config=SimpleNamespace(long_prefill_token_threshold=0),
+ mamba_partial_cache_hit=True,
+ mamba_fine_grained_prefix_cache=False,
+ hash_block_size=TAIL_HASH,
+ mamba_has_prefill_checkpoint_blocks=False,
+ mamba_prefill_checkpoint_alignment=None,
+ )
+ return Scheduler._mamba_block_aligned_split(stub, request, num_new, num_local_hit)
+
+
+def _tail_drain_copies(manager) -> None:
+ """What the scheduler does once a step's CoW copies have run: release
+ both endpoints' copy retentions."""
+ _, retained = manager.take_kv_cache_block_copies()
+ manager.block_pool.free_blocks(retained)
+
+
+def _tail_prefill(manager, request) -> int:
+ """Prefill to the prompt end in the chunks the scheduler would cut
+ (block ends, the partial-tail stop); returns the admitted hit length."""
+ computed_blocks, num_hit, _ = manager.get_computed_blocks(request)
+ first = True
+ while request.num_computed_tokens < request.num_tokens:
+ start = request.num_computed_tokens + (num_hit if first else 0)
+ num_new = _tail_split(
+ request, request.num_tokens - start, num_hit if first else 0
+ )
+ assert num_new > 0
+ blocks = manager.allocate_slots(
+ request,
+ num_new,
+ num_new_computed_tokens=num_hit if first else 0,
+ new_computed_blocks=computed_blocks if first else None,
+ num_lookahead_tokens=TAIL_SPEC,
+ )
+ assert blocks is not None, "prefill chunk did not fit"
+ request.num_computed_tokens = start + num_new
+ manager.new_step_starts()
+ _tail_drain_copies(manager)
+ first = False
+ return num_hit
+
+
+def _tail_decode(manager, request, steps: int) -> None:
+ """MTP K=3 decode steps, no drafts accepted."""
+ next_tok = 50000 + len(request.output_token_ids)
+ if request.num_computed_tokens == request.num_tokens:
+ request.append_output_token_ids(next_tok)
+ next_tok += 1
+ for _ in range(steps):
+ assert request.num_computed_tokens == request.num_tokens - 1
+ request.spec_token_ids = [next_tok + i for i in range(TAIL_SPEC)]
+ blocks = manager.allocate_slots(
+ request, 1 + TAIL_SPEC, num_lookahead_tokens=TAIL_SPEC
+ )
+ assert blocks is not None, "decode step did not fit"
+ request.spec_token_ids = []
+ request.num_computed_tokens += 1
+ request.append_output_token_ids([next_tok])
+ next_tok += 1
+ manager.new_step_starts()
+ _tail_drain_copies(manager)
+
+
+def _tail_tokens(seed: int, n: int) -> list[int]:
+ return [seed * 10000 + i for i in range(n)]
+
+
+def _tail_position(num_prompt_tokens: int) -> int:
+ """Where the prompt's partial-tail state is keyed (eagle shifts it one
+ unit below the last hash boundary)."""
+ return num_prompt_tokens // TAIL_HASH * TAIL_HASH - TAIL_HASH
+
+
+def _tail_followup(prev, user_tokens: int, seed: int):
+ """The next turn: the previous turn's prompt + its output + new text,
+ sized so that its tail lands strictly inside a block above the last
+ cacheable block end (the deployed case; a block-aligned tail is a
+ full-block key, not a partial one)."""
+ while True:
+ prompt = len(prev.all_token_ids) + user_tokens
+ tail = _tail_position(prompt)
+ last_block_end = prompt - prompt % TAIL_BLOCK - TAIL_BLOCK
+ if tail % TAIL_BLOCK != 0 and last_block_end < tail:
+ break
+ user_tokens += 1
+ return make_request(
+ prev.request_id + "+",
+ list(prev.all_token_ids) + _tail_tokens(seed, user_tokens),
+ TAIL_HASH,
+ sha256,
+ )
+
+
+def _tail_mamba(manager):
+ return manager.coordinator.single_type_managers[TAIL_MAMBA]
+
+
+def _tail_free_ids(manager) -> set[int]:
+ return {b.block_id for b in manager.block_pool.free_block_queue.get_all_free_blocks()}
+
+
+def _tail_assert_pool_clean(manager, num_blocks: int) -> None:
+ pool = manager.block_pool
+ assert pool.get_num_free_blocks() == num_blocks - 1 # all but the null block
+ assert all(blk.ref_cnt == 0 for blk in pool.blocks[1:])
+ mamba = _tail_mamba(manager)
+ assert not mamba._retained_checkpoints
+ assert not mamba._partial_hit_reqs
+ assert not mamba.req_to_blocks
+
+
+def test_partial_tail_resume_next_turn_hits_after_concurrent_allocation(tail_retain):
+ """Behaviour only (the observed miss): A1 resumed at A0's partial
+ tail; while A1 decodes, concurrent prefills pop every free block; A1
+ finishes; A2 must resume at A1's tail. Before the fix A2's hit is 0 --
+ a total miss on a prompt whose whole attention prefix is still cached."""
+ manager = _tail_manager(96)
+ pool = manager.block_pool
+ a0 = make_request("A0", _tail_tokens(1, 150), TAIL_HASH, sha256)
+ _tail_prefill(manager, a0)
+ _tail_decode(manager, a0, steps=4)
+ manager.free(a0)
+ _tail_drain_copies(manager)
+
+ a1 = _tail_followup(a0, 26, seed=2)
+ num_hit = _tail_prefill(manager, a1)
+ assert num_hit == _tail_position(a0.num_prompt_tokens) # a partial tail
+ assert num_hit % TAIL_BLOCK != 0
+ _tail_decode(manager, a1, steps=4)
+ pool.free_blocks(pool.get_new_blocks(pool.get_num_free_blocks())) # burst
+ manager.free(a1)
+ _tail_drain_copies(manager)
+
+ a2 = _tail_followup(a1, 20, seed=3)
+ _, num_hit, _ = manager.get_computed_blocks(a2)
+ assert all(
+ pool.get_cached_block(a1.block_hashes[i], [TAIL_ATTN])
+ for i in range(a1.num_prompt_tokens // TAIL_HASH)
+ )
+ assert num_hit == (_tail_position(a1.num_prompt_tokens) if tail_retain else 0)
+
+
+def test_partial_tail_resume_keeps_its_own_tail_under_concurrent_allocation(
+ tail_retain,
+):
+ """Turn 0 (A0) is a cold prefill; turn 1 (A1) resumes at A0's partial tail
+ (mid-block). A1 hashes no boundary state -- its replay boundary is below
+ its resume point -- so its own tail, moved into a CoW block by the chunk
+ after the tail stop, is the only GDN state its next turn can hit. Before
+ the fix the scheduler's post-copy release left that block at ref 0 in the
+ free queue while A1 still decoded; a concurrent prefill popped it and the
+ next turn (A2) got a TOTAL miss although every attention block of A1 was
+ still cached. With retention on, A1 holds the moved tail until it is
+ freed and A2 resumes at it. ``retain-off-control`` is the old behaviour
+ (and v2.5.0 fails the retain-on case the same way).
+ """
+ num_blocks = 96
+ manager = _tail_manager(num_blocks)
+ pool = manager.block_pool
+ mamba = _tail_mamba(manager)
+
+ a0 = make_request("A0", _tail_tokens(1, 150), TAIL_HASH, sha256)
+ assert _tail_prefill(manager, a0) == 0
+ _tail_decode(manager, a0, steps=4)
+ manager.free(a0)
+ _tail_drain_copies(manager)
+
+ # A1 resumes at A0's tail: a sub-block hit, so its first chunk copies the
+ # hit state into a private block (CoW).
+ a1 = _tail_followup(a0, 26, seed=2)
+ a1_tail = _tail_position(a1.num_prompt_tokens)
+ num_hit = _tail_prefill(manager, a1)
+ assert num_hit == _tail_position(a0.num_prompt_tokens)
+ assert num_hit % TAIL_BLOCK != 0
+ [tail_block] = pool.get_cached_block(
+ a1.block_hashes[a1_tail // TAIL_HASH - 1], [TAIL_MAMBA]
+ )
+ # The tail state was moved out of A1's table into the CoW block, and A1
+ # keyed no full-block boundary state of its own.
+ assert tail_block not in mamba.req_to_blocks.get(a1.request_id, [])
+ assert tail_block.block_hash_num_tokens == a1_tail
+ for position in range(TAIL_BLOCK, a1_tail, TAIL_BLOCK):
+ if position > num_hit:
+ assert (
+ pool.get_cached_block(
+ a1.block_hashes[position // TAIL_HASH - 1], [TAIL_MAMBA]
+ )
+ is None
+ )
+ _tail_decode(manager, a1, steps=4)
+
+ if tail_retain:
+ assert mamba._retained_checkpoints[a1.request_id] == (a1_tail, tail_block)
+ assert tail_block.ref_cnt == 1
+ assert tail_block.block_id not in _tail_free_ids(manager)
+ else:
+ # The exposure: cached-free while A1 still runs.
+ assert tail_block.ref_cnt == 0 and tail_block.block_hash is not None
+ assert tail_block.block_id in _tail_free_ids(manager)
+
+ # A burst of concurrent prefills pops every free block while A1 decodes.
+ taken = pool.get_new_blocks(pool.get_num_free_blocks())
+ assert (tail_block.block_hash is not None) is tail_retain
+ pool.free_blocks(taken)
+
+ # A1 finishes; its next turn arrives.
+ manager.free(a1)
+ _tail_drain_copies(manager)
+ a2 = _tail_followup(a1, 20, seed=3)
+ _, num_hit, _ = manager.get_computed_blocks(a2)
+ # Every attention block of A1's prompt is still cached in both worlds.
+ assert all(
+ pool.get_cached_block(a1.block_hashes[i], [TAIL_ATTN])
+ for i in range(a1.num_prompt_tokens // TAIL_HASH)
+ )
+ if tail_retain:
+ assert num_hit == a1_tail
+ else:
+ # FAILING CONTROL: total miss with the whole attention prefix cached.
+ assert num_hit == 0
+
+ # The next turn runs to completion on what it got; nothing leaks.
+ _tail_prefill(manager, a2)
+ _tail_decode(manager, a2, steps=2)
+ manager.free(a2)
+ _tail_drain_copies(manager)
+ _tail_assert_pool_clean(manager, num_blocks)
+
+
+def test_partial_tail_hit_admission_reserves_the_tail_swap(tail_retain):
+ """Full-sequence admission of a partial-tail follow-up reserves one block
+ per Mamba group above the per-step estimate (the held hit source and the
+ moved tail coexist for the swap); a block-aligned follow-up reserves none.
+ """
+ num_blocks = 96
+ manager = _tail_manager(num_blocks)
+ a0 = make_request("A0", _tail_tokens(1, 150), TAIL_HASH, sha256)
+ _tail_prefill(manager, a0)
+ _tail_decode(manager, a0, steps=2)
+ manager.free(a0)
+ _tail_drain_copies(manager)
+
+ a1 = _tail_followup(a0, 26, seed=2)
+ computed, num_hit, _ = manager.get_computed_blocks(a1)
+ assert num_hit % TAIL_BLOCK != 0
+
+ def need(apply_admission_cap: bool) -> int:
+ return manager.coordinator.get_num_blocks_to_allocate(
+ request_id=a1.request_id,
+ num_tokens=a1.num_tokens,
+ new_computed_blocks=computed.blocks,
+ num_encoder_tokens=0,
+ total_computed_tokens=num_hit,
+ num_local_computed_tokens=num_hit,
+ num_tokens_main_model=a1.num_tokens,
+ apply_admission_cap=apply_admission_cap,
+ )
+
+ assert need(True) == need(False) + (1 if tail_retain else 0)
+
+
+@pytest.mark.parametrize("deferred", [False, True], ids=["free", "pop_blocks_for_free"])
+@pytest.mark.parametrize("stop_at", ["after-hit-copy", "after-tail-copy"])
+def test_partial_tail_resume_freed_with_queued_copy_leaks_nothing(
+ tail_retain, deferred, stop_at
+):
+ """A request that resumed at a partial tail is freed (finish, abort or
+ preemption) while its CoW copy is still queued -- before the scheduler
+ has released the copy retentions. Whatever order the retentions and the
+ request's hold are released in, every block ends at ref 0 and the pool
+ returns to baseline; the superseded hit source ages instead of leaking.
+ """
+ num_blocks = 96
+ manager = _tail_manager(num_blocks)
+ pool = manager.block_pool
+ mamba = _tail_mamba(manager)
+
+ a0 = make_request("A0", _tail_tokens(1, 150), TAIL_HASH, sha256)
+ _tail_prefill(manager, a0)
+ _tail_decode(manager, a0, steps=2)
+ manager.free(a0)
+ _tail_drain_copies(manager)
+
+ a1 = _tail_followup(a0, 26, seed=2)
+ a1_tail = _tail_position(a1.num_prompt_tokens)
+ computed_blocks, num_hit, _ = manager.get_computed_blocks(a1)
+ assert 0 < num_hit < a1_tail and num_hit % TAIL_BLOCK != 0
+ [source] = pool.get_cached_block(
+ a0.block_hashes[num_hit // TAIL_HASH - 1], [TAIL_MAMBA]
+ )
+ assert source.ref_cnt == 0
+
+ # First chunk: the hit source is copied into A1's private block.
+ num_new = _tail_split(a1, a1.num_tokens - num_hit, num_hit)
+ assert manager.allocate_slots(
+ a1, num_new, num_hit, computed_blocks, num_lookahead_tokens=TAIL_SPEC
+ )
+ a1.num_computed_tokens = num_hit + num_new
+ manager.new_step_starts()
+ if tail_retain:
+ assert mamba._retained_checkpoints[a1.request_id] == (num_hit, source)
+ if stop_at == "after-tail-copy":
+ _tail_drain_copies(manager)
+ # Run to the chunk that moves A1's own tail into a CoW block.
+ while a1.num_computed_tokens <= a1_tail:
+ num_new = _tail_split(a1, a1.num_tokens - a1.num_computed_tokens)
+ assert manager.allocate_slots(a1, num_new, num_lookahead_tokens=TAIL_SPEC)
+ a1.num_computed_tokens += num_new
+ manager.new_step_starts()
+ if a1.num_computed_tokens <= a1_tail:
+ _tail_drain_copies(manager)
+ [tail_block] = pool.get_cached_block(
+ a1.block_hashes[a1_tail // TAIL_HASH - 1], [TAIL_MAMBA]
+ )
+ if tail_retain:
+ assert mamba._retained_checkpoints[a1.request_id] == (a1_tail, tail_block)
+ assert source.ref_cnt == 0 # superseded: ages, not leaked
+ assert source.block_hash is not None
+
+ # Freed with the copy still queued.
+ if deferred:
+ pool.free_blocks(manager.pop_blocks_for_free(a1))
+ else:
+ manager.free(a1)
+ assert a1.request_id not in mamba._retained_checkpoints
+ assert all(blk.ref_cnt >= 0 for blk in pool.blocks[1:])
+ # The copy's retentions are released afterwards.
+ _tail_drain_copies(manager)
+ assert source.ref_cnt == 0
+ _tail_assert_pool_clean(manager, num_blocks)
+
+
+def test_consumer_hold_follows_the_producers_moved_tail(tail_retain):
+ """Without the eagle drop a sibling can resume at a producer's tail while
+ that tail is still the producer's LIVE running block (published at the
+ tail stop, hit before the producer's next chunk). The consumer's hold
+ then pins the producer's block; when the producer's next chunk moves the
+ hashes into its CoW block, the hold must follow them -- it pins the
+ hashed state, never another request's running block -- and both
+ requests must still free cleanly.
+ """
+ num_blocks = 96
+ manager = _tail_manager(num_blocks, use_eagle=False)
+ pool = manager.block_pool
+ mamba = _tail_mamba(manager)
+
+ producer = make_request("P", _tail_tokens(1, 150), TAIL_HASH, sha256)
+ tail = producer.num_prompt_tokens // TAIL_HASH * TAIL_HASH # 144, no shift
+ computed, num_hit, _ = manager.get_computed_blocks(producer)
+ while producer.num_computed_tokens < tail:
+ # The real split gets the whole remainder and stops at the tail.
+ num_new = _tail_split(
+ producer, producer.num_tokens - producer.num_computed_tokens, use_eagle=False
+ )
+ assert producer.num_computed_tokens + num_new <= tail
+ assert manager.allocate_slots(
+ producer,
+ num_new,
+ num_new_computed_tokens=num_hit,
+ new_computed_blocks=computed,
+ num_lookahead_tokens=TAIL_SPEC,
+ )
+ producer.num_computed_tokens += num_new
+ computed, num_hit = None, 0
+ manager.new_step_starts()
+ _tail_drain_copies(manager)
+ [live] = pool.get_cached_block(
+ producer.block_hashes[tail // TAIL_HASH - 1], [TAIL_MAMBA]
+ )
+ assert live in mamba.req_to_blocks["P"] # the tail is keyed on the live block
+
+ consumer = make_request(
+ "C", list(producer.prompt_token_ids) + _tail_tokens(2, 30), TAIL_HASH, sha256
+ )
+ c_computed, c_hit, _ = manager.get_computed_blocks(consumer)
+ assert c_hit == tail
+ num_new = _tail_split(
+ consumer, consumer.num_tokens - c_hit, c_hit, use_eagle=False
+ )
+ assert manager.allocate_slots(
+ consumer, num_new, c_hit, c_computed, num_lookahead_tokens=TAIL_SPEC
+ )
+ consumer.num_computed_tokens = c_hit + num_new
+ if tail_retain:
+ assert mamba._retained_checkpoints["C"] == (tail, live)
+
+ # The producer's next chunk moves the tail hashes into its CoW block.
+ manager.new_step_starts()
+ _tail_drain_copies(manager)
+ num_new = _tail_split(
+ producer, producer.num_tokens - producer.num_computed_tokens, use_eagle=False
+ )
+ assert manager.allocate_slots(producer, num_new, num_lookahead_tokens=TAIL_SPEC)
+ producer.num_computed_tokens += num_new
+ [moved] = pool.get_cached_block(
+ producer.block_hashes[tail // TAIL_HASH - 1], [TAIL_MAMBA]
+ )
+ assert moved is not live and live.block_hash is None
+ if tail_retain:
+ assert mamba._retained_checkpoints["C"] == (tail, moved)
+ assert mamba._retained_checkpoints["P"] == (tail, moved)
+ manager.new_step_starts()
+ _tail_drain_copies(manager)
+ # The live block is referenced by the producer's table alone again.
+ assert live.ref_cnt == 1
+
+ _tail_decode(manager, producer, steps=2)
+ manager.free(producer)
+ _tail_drain_copies(manager)
+ while consumer.num_computed_tokens < consumer.num_tokens:
+ num_new = _tail_split(
+ consumer,
+ consumer.num_tokens - consumer.num_computed_tokens,
+ use_eagle=False,
+ )
+ assert manager.allocate_slots(
+ consumer, num_new, num_lookahead_tokens=TAIL_SPEC
+ )
+ consumer.num_computed_tokens += num_new
+ manager.new_step_starts()
+ _tail_drain_copies(manager)
+ _tail_decode(manager, consumer, steps=2)
+ manager.free(consumer)
+ _tail_drain_copies(manager)
+ _tail_assert_pool_clean(manager, num_blocks)
diff --git a/tests/v1/core/test_mamba_checkpoint_retention.py b/tests/v1/core/test_mamba_checkpoint_retention.py
index 9d0d440..502e68b 100644
--- a/tests/v1/core/test_mamba_checkpoint_retention.py
+++ b/tests/v1/core/test_mamba_checkpoint_retention.py
@@ -548,8 +548,9 @@ def test_mtp_chunked_prefill_aligned_prompt_retains_newest_boundary_only(
[hi] = pool.get_cached_block(hi_hash, [gid])
assert _hashed_cached(manager, lo) # superseded / never held: ages
if retain:
- idx, held = _mamba(manager, gid)._retained_checkpoints["A"]
- assert idx == 2 and held is hi
+ # Keyed by the hashed token position, not block index.
+ position, held = _mamba(manager, gid)._retained_checkpoints["A"]
+ assert position == 3 * BLOCK and held is hi
assert hi.ref_cnt == 1
else:
assert _hashed_cached(manager, hi)
diff --git a/vllm/v1/core/kv_cache_coordinator.py b/vllm/v1/core/kv_cache_coordinator.py
index 7537ccd..b58aa96 100644
--- a/vllm/v1/core/kv_cache_coordinator.py
+++ b/vllm/v1/core/kv_cache_coordinator.py
@@ -248,7 +248,10 @@ class KVCacheCoordinator(ABC):
# the free queue that check reads.
num_blocks_to_allocate += (
manager.get_num_retained_checkpoint_blocks_to_reserve(
- request_id, num_tokens_main_model, new_computed_blocks[i]
+ request_id,
+ num_tokens_main_model,
+ new_computed_blocks[i],
+ num_local_computed_tokens,
)
)
return num_blocks_to_allocate
diff --git a/vllm/v1/core/single_type_kv_cache_manager.py b/vllm/v1/core/single_type_kv_cache_manager.py
index ca390ef..649f0a4 100644
--- a/vllm/v1/core/single_type_kv_cache_manager.py
+++ b/vllm/v1/core/single_type_kv_cache_manager.py
@@ -611,6 +611,7 @@ class SingleTypeKVCacheManager(ABC):
request_id: str,
num_tokens: int,
new_computed_blocks: Sequence[KVCacheBlock] = (),
+ num_local_computed_tokens: int = 0,
) -> int:
"""Blocks the admission gate must add for checkpoints this request
will hold outside its block table (0 for every manager but align-mode
@@ -1673,7 +1674,24 @@ class MambaManager(SingleTypeKVCacheManager):
and self.enable_caching
and envs.VLLM_E2_MAMBA_RETAIN_CHECKPOINT
)
- # {request_id: (logical block index, block)}
+ # {request_id: (hashed token position, block)}: the newest hashed
+ # state the request resumed from or produced, held with one ref of
+ # its own (ordered by ``block_hash_num_tokens`` rather than
+ # block index so a sub-block partial-tail key sorts correctly against
+ # full-block boundary states).
+ #
+ # With ``--prefix-match-unit`` below the block size a request
+ # that resumed at a partial tail (mid-block) never hashes a boundary
+ # state: the replay boundary lies below its resume point. Its only
+ # reusable GDN state is its own partial-tail checkpoint, which the
+ # next chunk moves into a CoW block in no block table; the scheduler
+ # drops the copy's retention refs once the copy has run, so that
+ # block sat at ref 0 in the free queue for the rest of the request,
+ # ahead of its attention blocks, and concurrent prefills evicted it
+ # (measured: 7/61 follow-ups with cached_tokens 0 at unit 64, every
+ # one after a partial-tail resume; none at unit 4096). The CoW paths
+ # therefore hold their hashed endpoint here too: the moved tail for
+ # a running request, and the hit source a new request copies from.
self._retained_checkpoints: dict[str, tuple[int, KVCacheBlock]] = {}
if self.mamba_cache_mode == "align" and self.enable_caching:
# The A/B evidence line: boot logs must show which arm ran.
@@ -1682,6 +1700,16 @@ class MambaManager(SingleTypeKVCacheManager):
"(VLLM_E2_MAMBA_RETAIN_CHECKPOINT)",
"on" if self._retain_checkpoint else "off",
)
+ if (
+ self._retain_checkpoint
+ and self.block_size > self.block_pool.hash_block_size
+ ):
+ logger.info_once(
+ "Mamba align: each request holds its partial-tail CoW checkpoint "
+ "until it is freed (hash unit %d, block %d)",
+ self.block_pool.hash_block_size,
+ self.block_size,
+ )
def _retire_state_blocks(
self, request_id: str, retired: list[tuple[int, KVCacheBlock]]
@@ -1696,13 +1724,16 @@ class MambaManager(SingleTypeKVCacheManager):
"""
if self._retain_checkpoint:
newest: tuple[int, KVCacheBlock] | None = None
- for idx, block in retired:
- if block.block_hash is not None and (
- newest is None or idx > newest[0]
- ):
- newest = (idx, block)
+ for _, block in retired:
+ if block.block_hash is None:
+ continue
+ position = block.block_hash_num_tokens
+ assert position is not None
+ if newest is None or position > newest[0]:
+ newest = (position, block)
held = self._retained_checkpoints.get(request_id)
if newest is not None and (held is None or newest[0] > held[0]):
+ # The retired block's table ref becomes the hold's ref.
self._retained_checkpoints[request_id] = newest
retired = [entry for entry in retired if entry[1] is not newest[1]]
if held is not None:
@@ -1711,6 +1742,43 @@ class MambaManager(SingleTypeKVCacheManager):
if retired:
self.block_pool.free_blocks([block for _, block in retired])
+ def _hold_checkpoint(self, request_id: str, block: KVCacheBlock) -> bool:
+ """Hold ``block`` (a hashed state outside the request's table) as the
+ request's prefix checkpoint, taking one extra ref for the hold.
+
+ Only the newest position is held: an older one is left alone (it ages
+ from wherever it is), a superseded one is released here. The hold's
+ ref is returned by ``pop_retained_checkpoints`` -> ``free_blocks``.
+ Returns whether the block is now held.
+ """
+ if not self._retain_checkpoint or block.is_null or block.block_hash is None:
+ return False
+ position = block.block_hash_num_tokens
+ assert position is not None
+ held = self._retained_checkpoints.get(request_id)
+ if held is not None and (held[1] is block or held[0] >= position):
+ return False
+ self.block_pool.touch([block])
+ self._retained_checkpoints[request_id] = (position, block)
+ if held is not None:
+ self.block_pool.free_blocks([held[1]])
+ return True
+
+ def _follow_moved_hash(
+ self, owner_id: str, source_block: KVCacheBlock, cow_block: KVCacheBlock
+ ) -> None:
+ """``owner_id`` just moved ``source_block``'s hashes to ``cow_block``
+ and keeps writing ``source_block``. A request that resumed at that
+ tail while it was still the owner's live block holds the source for
+ those hashes; move its hold to the copy, so it pins the hashed state
+ and not another request's running block.
+ """
+ for request_id, (position, block) in list(self._retained_checkpoints.items()):
+ if request_id != owner_id and block is source_block:
+ self.block_pool.touch([cow_block])
+ self._retained_checkpoints[request_id] = (position, cow_block)
+ self.block_pool.free_blocks([source_block])
+
def pop_retained_checkpoints(self, request_id: str) -> list[KVCacheBlock]:
if self.mamba_cache_mode != "align":
return []
@@ -1722,16 +1790,25 @@ class MambaManager(SingleTypeKVCacheManager):
request_id: str,
num_tokens: int,
new_computed_blocks: Sequence[KVCacheBlock] = (),
+ num_local_computed_tokens: int = 0,
) -> int:
# A request that already holds a checkpoint only ever swaps it. One
# that does not will hold one once a hashed state retires, which needs
# at least one state block behind the running one.
- if (
- not self._retain_checkpoint
- or request_id in self._retained_checkpoints
- or num_tokens <= self.block_size
- ):
+ if not self._retain_checkpoint or request_id in self._retained_checkpoints:
return 0
+ # A sub-block (partial-tail) hit holds the hit source only
+ # until the request's own tail is moved into a CoW block that is held
+ # in its place; at that step both are referenced, so the request's
+ # lifetime peak is one block above what the hit brought (whatever the
+ # prompt length: the tail CoW happens inside the first block too).
+ if self._has_partial_local_hit(new_computed_blocks, num_local_computed_tokens):
+ return 1
+ if num_tokens <= self.block_size:
+ # No state block retires behind the running one, but a prompt
+ # whose tail is keyed inside the block still moves that tail into
+ # a held CoW block when the hash unit is finer than the block.
+ return int(self.block_pool.hash_block_size < self.block_size)
# A prefix hit already brings the block that becomes the held
# checkpoint -- the hit state, counted by get_num_blocks_to_allocate as
# an evictable computed block (or already referenced elsewhere) -- and
@@ -2166,6 +2243,7 @@ class MambaManager(SingleTypeKVCacheManager):
# overwrites source_block.
assert req_blocks[block_idx] is source_block
self.block_pool.move_block_hashes(source_block, cow_block)
+ self._follow_moved_hash(request_id, source_block, cow_block)
self._pending_cow_copies.append((source_block, cow_block))
source_block.ref_cnt += 1
producer_tail = self._producer_partial_tail_reqs.pop(
@@ -2189,9 +2267,20 @@ class MambaManager(SingleTypeKVCacheManager):
# The moved entry is only filled by this step's
# copy, so defer same-step hits on it.
self.cached_blocks_this_step.add(cow_block.block_hash)
+ # The moved tail is the request's newest
+ # reusable state and lives in no block table; hold it
+ # past the copy's retention so the request's next
+ # turn can resume at it (see __init__).
+ self._hold_checkpoint(request_id, cow_block)
else:
self._apply_cow(request_id, block_idx, source_block, cow_block)
returned_blocks = [cow_block] + returned_blocks
+ # The hit source keeps the hash while the
+ # request advances its private copy; hold it until
+ # the request's own tail supersedes it, so a request
+ # that stops early (preempted, aborted, block-aligned
+ # prompt) still leaves the state it resumed from.
+ self._hold_checkpoint(request_id, source_block)
req_blocks.extend(new_blocks)
self._allocated_block_reqs.add(request_id)
self._partial_hit_reqs.pop(request_id, None)
--
2.43.0
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