[GG] feat(kv-offload): bound filesystem tier capacity - #165
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Add an opt-in max_cache_size_bytes limit to the filesystem secondary tier. Track runtime LRU state, reserve capacity across concurrent writers, and pin lookup and queued-load sources so eviction cannot race promotion. Index and trim existing block files on startup, publish removal events before replacement stores, and document that bounded mode requires exclusive ownership of its cache namespace. Assisted-by: OpenAI Codex Signed-off-by: Derek Yates <derek.yates@live.com>
📝 WalkthroughWalkthroughThe filesystem KV tier adds an optional byte capacity limit with startup indexing, LRU eviction, pin-aware concurrent stores and loads, synchronized event handling, and expanded tests and documentation. ChangesFilesystem cache capacity
Estimated code review effort: 4 (Complex) | ~45 minutes Sequence Diagram(s)sequenceDiagram
participant Request
participant FileSystemTierManager
participant Filesystem
participant KVEvents
Request->>FileSystemTierManager: submit_store
FileSystemTierManager->>FileSystemTierManager: reserve capacity
FileSystemTierManager->>Filesystem: evict unpinned LRU blocks
FileSystemTierManager->>Filesystem: write bounded block
Filesystem-->>FileSystemTierManager: store completion
FileSystemTierManager->>KVEvents: record removal event
FileSystemTierManager-->>Request: return completed job
Suggested reviewers: 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches 💡 1🛠️ Fix failing CI checks 💡
🧪 Generate unit tests (beta)
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Runtime validation update (CN3, 2026-07-23): the bounded tier ran through the full cold long-context ladder while an ordered inotify monitor tracked both completed block files and in-flight temporary files. Across 41,334 filesystem events, observed physical cache high-water was 8,589,111,296 bytes against an 8,589,934,592-byte cap: 823,296 bytes under, with zero observed violations. This directly answers the pending-byte question: temporary writes did not push the namespace over capacity. The monitor emitted 7,275 coverage warnings because it was attached to an already populated dynamic directory tree; that limits the monitor formal verdict but does not change the measured ordered high-water. Together with the 71 focused tests, concurrent-writer reservation tests, startup indexing tests, and sustained runtime turnover, the pending runtime gate is complete and this PR is ready for review. |
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🧹 Nitpick comments (2)
vllm/v1/kv_offload/tiering/fs/manager.py (2)
449-484: 🚀 Performance & Scalability | 🔵 Trivial | 💤 Low valueEviction loop is O(K·N) on the startup-trim path.
list(self._cache_lru.items())is rebuilt on every outerwhileiteration and the inner loop breaks after a single eviction, so trimming K blocks from an N-entry index costs O(K·N). Runtime stores evict ~1 block each (fine), but trimming a large oversized namespace at startup can be slow. Since the LRU is oldest-first and no pins exist during initialization, you could iterate the ordered view once. Optional.🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the rest with a brief reason, keep changes minimal, and validate. In `@vllm/v1/kv_offload/tiering/fs/manager.py` around lines 449 - 484, Optimize _evict_until_fits_locked by avoiding reconstruction of self._cache_lru.items() and restarting the scan after each eviction. Preserve oldest-first eviction and existing pinned-entry and filesystem-error handling, while using a single ordered traversal during startup trimming; retain the current failure result when no evictable entry can satisfy required_bytes.
251-260: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick winAdd
strict=to all fourzip(job_metadata.keys, job_metadata.block_ids)calls (ruff B905). These pair keys with their block offsets and are expected to be equal-length;strict=Trueclears the lint gate and turns any future length mismatch into a loud error instead of a silently short task set.
vllm/v1/kv_offload/tiering/fs/manager.py#L251-L260: addstrict=Trueto bothzip()calls insubmit_store.vllm/v1/kv_offload/tiering/fs/manager.py#L275-L275: addstrict=Trueto thezip()in the unboundedsubmit_loadbranch.vllm/v1/kv_offload/tiering/fs/manager.py#L296-L296: addstrict=Trueto thezip()in the boundedsubmit_loadbranch.Note
zip(strict=...)requires Python 3.10+; confirm the repo's declared target and rufftarget-versionallow it.🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the rest with a brief reason, keep changes minimal, and validate. In `@vllm/v1/kv_offload/tiering/fs/manager.py` around lines 251 - 260, Update both zip calls in submit_store and the zip calls in the unbounded and bounded submit_load branches in vllm/v1/kv_offload/tiering/fs/manager.py (lines 251-260, 275, and 296) to use strict=True, preserving the existing key/block pairing. Confirm the repository Python target and Ruff target-version support Python 3.10 or newer.Source: Linters/SAST tools
🤖 Prompt for all review comments with AI agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.
Nitpick comments:
In `@vllm/v1/kv_offload/tiering/fs/manager.py`:
- Around line 449-484: Optimize _evict_until_fits_locked by avoiding
reconstruction of self._cache_lru.items() and restarting the scan after each
eviction. Preserve oldest-first eviction and existing pinned-entry and
filesystem-error handling, while using a single ordered traversal during startup
trimming; retain the current failure result when no evictable entry can satisfy
required_bytes.
- Around line 251-260: Update both zip calls in submit_store and the zip calls
in the unbounded and bounded submit_load branches in
vllm/v1/kv_offload/tiering/fs/manager.py (lines 251-260, 275, and 296) to use
strict=True, preserving the existing key/block pairing. Confirm the repository
Python target and Ruff target-version support Python 3.10 or newer.
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📒 Files selected for processing (3)
docs/features/kv_offloading_usage.mdtests/v1/kv_offload/tiering/test_fs_tier.pyvllm/v1/kv_offload/tiering/fs/manager.py
Review: bound filesystem tier capacityChecked out locally (single commit Verdict: approve with nits. The capacity-bounding design is sound, the concurrency invariants are correct, the change is backward-compatible, and the test coverage targets the right races. Remaining items are minor. Strengths
Issues1. Valid CodeRabbit nit — 2. Valid CodeRabbit nit — O(K·N) startup trim (manager.py:449–484). 3. I/O under the capacity lock — worth a comment (manager.py:460, 493). 4. Load-failure emits 5. Bounded 6. Pin reclamation depends on framework callback (docs). Usable capacity permanently degrades if the engine ever fails to call 7. Test gaps. No test exercises #4 (load failure while the source is pinned by another consumer) or shutdown with in-flight load jobs (code releases pins at Tiny typing nit. The core invariant — never exceed the limit, never evict an in-use source, fail with |
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malaiwah
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Independent appliance-side review: I found no P0/data-corruption issue in the steady-state reservation or request/load pin-transfer design. The bounded tier looks promising, but I recommend addressing the startup-scaling and crash-recovery findings below before carrying it into the turnkey image. A few production gates are also still missing for our GLM-5.2 EXL3 use: startup against a realistically populated 1 TB namespace (including a large downward capacity change); SIGKILL during 16–32 concurrent writes followed by stale-temp recovery; clean restart with fixed PYTHONHASHSEED and an actual NVMe promotion; corrupt/truncated/missing-file recovery with kv_load_failure_policy=recompute; physical NVMe exhaustion; concurrent C1–C8 promotion+eviction; and real TP4 EXL3 mixed-MLA DCP2/DCP4 validation. It would also help to expose resident/reserved-byte gauges and eviction/ENOSPC/startup-trim counters. Overall recommendation: wait, not reject—fix the two operational issues, then qualify it opt-in on the exact GG image.
| > self._max_cache_size_bytes | ||
| ): | ||
| evicted = False | ||
| for key, size in list(self._cache_lru.items()): |
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P1: Startup trimming becomes quadratic for a large populated namespace. _initialize_capacity_index() loads every entry, then this loop rebuilds list(self._cache_lru.items()) and restarts from the oldest entry after every single deletion. Reducing a 1 TB namespace by tens or hundreds of thousands of blocks can therefore make startup effectively unbounded on the scheduler thread; the current three-file trim test cannot expose it. Could startup use one ordered pass (or repeatedly pop the oldest unpinned entry without reconstructing the complete list), while retaining the current pinned/error behavior for steady-state eviction?
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Fixed in 8cee971. The eviction helper now takes one oldest-first snapshot of keys and scans each candidate at most once per call; pinned entries and unlink failures remain in place and later evictable entries are still considered. A focused regression combines a pinned oldest entry with an injected unlink failure and asserts that the failing candidate is attempted exactly once while enough later entries are removed. Runtime manager pin: MD5 db623944a195ebb601d647f4325349bf; SHA-256 bebaec75f07b53d06a74bb55e64b7963c89f0e78287defa6b5c32d66f0417352.
| for filename in filenames: | ||
| path = os.path.join(dir_path, filename) | ||
| key = self._key_from_cache_path(path) | ||
| if key is None: |
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P2: Crash-leftover temporary files are ignored by startup recovery and capacity accounting because _key_from_cache_path() accepts only final .bin records. Normal exception cleanup is good, but SIGKILL, host reset, or power loss can leave <dest><random>.tmp files indefinitely; repeated crashes can consume NVMe outside max_cache_size_bytes. Please consider sweeping only FileMapper-owned stale temp names at startup, or placing them in an owned temp directory that can be safely recovered/accounted. A SIGKILL-during-concurrent-writes restart test would cover this contract.
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Fixed in 8cee971. Bounded-mode startup now recognizes only FileMapper-owned writer leftovers whose derived destination is a valid cache path and whose suffix has the exact decimal temporary-file shape. It removes those files before indexing, preserves unrelated temporary files, logs the cleanup count, and fails startup if an owned stale file cannot be removed. Both selective cleanup and fail-closed behavior have focused tests.
| locality=self.locality, | ||
| if self._max_cache_size_bytes is not None: | ||
| with self._capacity_cv: | ||
| keys = [key for key in keys if key in self._cache_lru] |
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P3: KV-event ordering is not fully serialized across concurrent jobs. Eviction/removal events are appended immediately by worker activity, while BlockStored is published later during scheduler polling here. A replacement can evict A before A's completed store job is polled; this resident filter then suppresses Stored(A), leaving observers with Removed(A) without a preceding store. Cache state remains correct, but consumers expecting a balanced ordered stream can be confused. Either document removal as idempotent/state-only, or serialize stored/removal publication for a key.
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Resolved in 8cee971 using the contract/documentation option from this finding. Removal is now explicitly an idempotent state invalidation at the OffloadingEvent type and in the consumer documentation; consumers ignore removals for unknown state. The existing resident filter is retained so an already-evicted key never produces a stale store event. A deterministic regression completes store A without polling, evicts A while storing B, then verifies the stream is Removed(A), Stored(B), with no stale Stored(A).
Corroboration on the three inline findingsChecked out locally at P1 (startup O(K·N) trim) — confirmed, and agree on the severity upgrade
P2 (crash-leftover temp files) — confirmed, and this is genuinely newVerified the chain:
Neither CodeRabbit nor I raised this — good catch. One precision worth pinning down: this is not a P3 (unbalanced KV-event stream) — confirmed, same mechanism as my #5The trace holds: store J completes → A enters On the review body's supporting claims
Net: all three inline findings are valid against the code. P2 is the highest-value addition to the thread — a real crash-recovery gap the other reviews missed. |
Trim oversized namespaces in one ordered pass, remove FileMapper-owned stale temporary files at startup, and define removal events as idempotent state invalidations. Add focused regression coverage for scan complexity, fail-closed stale-temp cleanup, and eviction before store-result polling. Assisted-by: OpenAI Codex Signed-off-by: derek <derek.yates@live.com>
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🧹 Nitpick comments (4)
vllm/v1/kv_offload/tiering/fs/manager.py (3)
420-480: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick winDocument that runtime (mid-session)
.tmpgrowth is still unbounded between restarts.This startup pass only reclaims stale
.tmpfiles left from a previous crash; a.tmpfile created during the current session that then crashes before the next restart is invisible to_cache_size_bytes/max_cache_size_bytesuntil the following startup scan. Worth a short note (docstring onmax_cache_size_bytesor here) clarifying that the byte limit governs only completed.binfiles, so transient.tmpwrites can still push total disk usage above the configured cap between restarts.📝 Suggested doc addition
max_cache_size_bytes: Optional byte limit for this tier's block files. When set, the least-recently-used unpinned blocks are removed before new blocks are stored. The limit applies only to this model/configuration namespace and requires exclusive ownership of that namespace by this vLLM instance. + Note: the limit governs completed ``.bin`` files only; an + in-flight ``.tmp`` write that crashes mid-session is not + reclaimed against this cap until the next restart's startup + scan.🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the rest with a brief reason, keep changes minimal, and validate. In `@vllm/v1/kv_offload/tiering/fs/manager.py` around lines 420 - 480, Add a brief documentation note to `_initialize_capacity_index` or the `max_cache_size_bytes` configuration describing that the limit applies only to completed `.bin` files tracked in `_cache_size_bytes`; runtime `.tmp` files are not counted and may temporarily exceed the configured disk cap until a subsequent startup scan.
481-517: 🚀 Performance & Scalability | 🔵 TrivialConsider exposing capacity/eviction metrics.
There's currently no counter/gauge for resident bytes vs.
max_cache_size_bytes, eviction count, orENOSPCfail-closed events. Given this feature's failure mode (storage rejected once all resident blocks are pinned) is silent from an operator's perspective until requests start failing, surfacing_cache_size_bytes/eviction counts as metrics would materially help diagnosing capacity pressure in production.🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the rest with a brief reason, keep changes minimal, and validate. In `@vllm/v1/kv_offload/tiering/fs/manager.py` around lines 481 - 517, Add metrics for resident cache bytes, configured max capacity, eviction count, and fail-closed ENOSPC events, integrating them with the existing metrics mechanism used by the filesystem tier manager. Update the eviction path in _evict_until_fits_locked to record successful evictions and keep resident-byte metrics synchronized, and increment the ENOSPC metric whenever capacity cannot be satisfied because entries remain pinned.
481-517: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick winNice fix for the quadratic startup trim — consider documenting the lock-hold contract.
Scanning
tuple(self._cache_lru)once and evicting until the target is met resolves the previous quadratic rebuild-per-deletion issue;test_capacity_eviction_scans_each_candidate_oncecovers this well. Since eviction now runsos.remove()(metadata-only unlink, no data I/O) while holding_capacity_cvfor potentially many candidates, a short comment noting that only metadata syscalls occur under this lock would help future maintainers reason about lock-hold duration without re-litigating it.🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the rest with a brief reason, keep changes minimal, and validate. In `@vllm/v1/kv_offload/tiering/fs/manager.py` around lines 481 - 517, Add a concise comment near the os.remove call in _evict_until_fits_locked documenting that eviction holds _capacity_cv while performing only metadata-only unlink operations, with no data I/O. Keep the existing single-scan eviction behavior unchanged.tests/v1/kv_offload/tiering/test_fs_tier.py (1)
865-883: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick winTwo previously-requested regression tests still appear missing.
The commit message states this round adds tests for "scan complexity, stale-temp cleanup, and eviction before store-result polling," but the earlier follow-up list also asked for tests covering (1) a load failure while the key remains pinned, and (2)
shutdown()with in-flight loads still holding pins. Neither scenario is visible among the new tests. Worth adding coverage for_load_block_bounded's exception path under an active pin, and forshutdown()'s pin-release loop racing an in-flight load.🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the rest with a brief reason, keep changes minimal, and validate. In `@tests/v1/kv_offload/tiering/test_fs_tier.py` around lines 865 - 883, Add regression tests covering a load failure while the key remains pinned and shutdown with in-flight loads still holding pins. Exercise _load_block_bounded’s exception path under an active pin, then verify the pin is released and the failure is handled; separately start an in-flight load, call shutdown(), and assert the shutdown pin-release loop completes safely.
🤖 Prompt for all review comments with AI agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.
Nitpick comments:
In `@tests/v1/kv_offload/tiering/test_fs_tier.py`:
- Around line 865-883: Add regression tests covering a load failure while the
key remains pinned and shutdown with in-flight loads still holding pins.
Exercise _load_block_bounded’s exception path under an active pin, then verify
the pin is released and the failure is handled; separately start an in-flight
load, call shutdown(), and assert the shutdown pin-release loop completes
safely.
In `@vllm/v1/kv_offload/tiering/fs/manager.py`:
- Around line 420-480: Add a brief documentation note to
`_initialize_capacity_index` or the `max_cache_size_bytes` configuration
describing that the limit applies only to completed `.bin` files tracked in
`_cache_size_bytes`; runtime `.tmp` files are not counted and may temporarily
exceed the configured disk cap until a subsequent startup scan.
- Around line 481-517: Add metrics for resident cache bytes, configured max
capacity, eviction count, and fail-closed ENOSPC events, integrating them with
the existing metrics mechanism used by the filesystem tier manager. Update the
eviction path in _evict_until_fits_locked to record successful evictions and
keep resident-byte metrics synchronized, and increment the ENOSPC metric
whenever capacity cannot be satisfied because entries remain pinned.
- Around line 481-517: Add a concise comment near the os.remove call in
_evict_until_fits_locked documenting that eviction holds _capacity_cv while
performing only metadata-only unlink operations, with no data I/O. Keep the
existing single-scan eviction behavior unchanged.
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📒 Files selected for processing (4)
docs/features/kv_offloading_usage.mdtests/v1/kv_offload/tiering/test_fs_tier.pyvllm/v1/kv_offload/base.pyvllm/v1/kv_offload/tiering/fs/manager.py
🚧 Files skipped from review as they are similar to previous changes (1)
- docs/features/kv_offloading_usage.md
2 participants
Summary
max_cache_size_bytescapacity to the filesystem secondary tier.Why
The filesystem tier currently grows without a configured retention bound. On a local NVMe tier, this can fill the device and turn normal KV churn into
ENOSPCfailures outside the cache policy.Bounded mode evicts the least-recently-used unpinned block before admitting a store. If every resident block is pinned by an active request or load job, that store fails with
ENOSPCinstead of evicting an in-use source or exceeding the configured limit. Leavingmax_cache_size_bytesunset preserves the existing path.This does not duplicate an open downstream or upstream capacity PR. The open upstream worker-transfer and CPU-policy changes address different tiers and ownership layers; none provides a byte bound for the local filesystem tier.
Forward-port and review history
The
dev/gilded-gnosisversions of the original three input files were byte-for-byte identical to the v19 inputs for commitd74c0a6c. Commita1f5cc6cwas therefore an exact replay with no conflict resolution or semantic adaptation.Follow-up commit
8cee971baddresses all three findings from the independent review:_evict_until_fits_lockednow makes one oldest-first pass over a stable key snapshot. It attempts each pinned, unremovable, or evictable entry at most once per admission call instead of rebuilding and restarting anO(N)item list after every eviction.<valid-final-.bin>_<decimal>.tmp, removes those stale files before indexing, preserves unrelated files, and fails startup if an owned stale file cannot be removed.BlockRemovedis now explicitly an idempotent state invalidation. A removal may have no preceding store in the current stream, including restart trimming and eviction before scheduler completion polling. The resident filter continues to suppress a staleBlockStoredevent after eviction; this behavior is documented at the raw event type and consumer-facing documentation and covered by a deterministic regression test.Validation
Focused tests on the repaired v20 tree:
VLLM_TARGET_DEVICE=empty python -m pytest -q tests/v1/kv_offload/tiering/test_fs_tier.py: 36 passed, 2 skipped platform-extension cellsVLLM_TARGET_DEVICE=empty python -m pytest -q tests/v1/kv_offload/tiering/test_factory.py tests/v1/kv_offload/tiering/test_tiering_offloading.py: 37 passedpre-commiton all four changed files: all applicable hooks passed, including Ruff, mypy, markdownlint, SPDX, forbidden-import, and configuration checkscompileall: passedgit diff --check: passedThe filesystem suite was run on ARM macOS with vLLM's
skip_global_cleanuptest marker because PyTorch 2.11's unrelated MPS allocator asserts in the global teardown fixture. All test bodies passed. The two skipped cells require the optional Linux filesystem lookup extension.Existing target-system capacity evidence for the underlying reservation/eviction path:
The ordered-event monitor tracks completed and in-flight temporary files. This replaced an earlier non-atomic directory sampler whose apparent transient overshoots were measurement artifacts.
Model-output evaluation is not applicable because this change controls filesystem cache retention, recovery, and event reporting, not model computation.
Source pins
8cee971bef4f483904d86d196a39da1aa9f7c106a1f5cc6cd0bcbcedfc607f98afbd8883ea3a3d5avllm/v1/kv_offload/tiering/fs/manager.pydb623944a195ebb601d647f4325349bfbebaec75f07b53d06a74bb55e64b7963c89f0e78287defa6b5c32d66f0417352vllm/v1/kv_offload/base.py2048bd632e66e599c48a65650694ae5e7a506dc168c4b7b76a992ee81e1b1c2a2e856c49be51287ab1b8b1be6b2e5f12tests/v1/kv_offload/tiering/test_fs_tier.pyadf9a247088f0ec434c076023506700e4d4f458208c266ad8a143561d4e2c6807c558be659f6bc0f31d76b22a4750f48docs/features/kv_offloading_usage.md682fbaaa361f68e9191150c2d2e6be4cf49137c5a260286bc31a20eada70a804f29a35291206ec4671fa7368a3326a69AI assistance
OpenAI Codex assisted with investigation, implementation, testing, and PR drafting. The human submitter will review every changed line and the recorded evidence before merge.
Summary by CodeRabbit
New Features
Bug Fixes
Documentation