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storage: add optional chunk file-slot pool to bound filesystem slab growth - #12572
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…ead-safe Signed-off-by: Dmitri Pavlov <dpavlov@perforce.com>
Signed-off-by: Dmitri Pavlov <dpavlov@perforce.com>
Signed-off-by: Dmitri Pavlov <dpavlov@perforce.com>
Signed-off-by: Dmitri Pavlov <dpavlov@perforce.com>
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Test pool_slot_name_parse... |
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100% tests passed, 0 tests failed out of 6 Total Test time (real) = 0.47 sec |
Integration results - pool fix on master (5.2.0 line), 2026-10-12(unit/sanitizer section refreshed 2026-10-13 after review hardening) Image: Pipeline: the 100-stream tail rig - 100 tail log files at 15 MB/s -> filesystem A/B via
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| setting | slab_reclaimable 300 s |
slope | chunk files |
|---|---|---|---|
storage.file_pool_size unset |
+1446 KB | ~17.4 MB/h | unique names, churning |
storage.file_pool_size 2048 |
+196 KB | ~2.4 MB/h | 100% slot-*.flb, reused |
Startup log reflects the setting:
[storage] ver=1.5.4, type=memory+filesystem, sync=normal, checksum=off,
max_chunks_up=32, file_pool_size=2048
Restart recovery (option on)
- Ran with the option off + HEC delay to build a backlog: 36 pending
stock-named chunk files. - Stopped the container, restarted with
storage.file_pool_size 2048:could not retrieve chunk tagerrors: 0- all 36 legacy chunks delivered and unlinked (unique files 36 -> 0)
- 36 slot files remain (the reusable pool)
Opt-out after opt-in
- Ran with the pool on, then stopped with 35 slot chunks pending.
- Restarted with the option unset (stock behaviour): 0 tag errors, HEC event
counter kept increasing (chunks recovered/delivered), no errors.
Unit / sanitizers
- chunkio
ctest: 6/6 suites;fs_pool: 20/20 tests, including the
review additionspool_counter_balance(max_chunks_up limit, failed
down-chunk read, failed corrupt-slot open and pool-disabled delete-by-name)
andpool_threaded_max_chunks(8 threads racing the atomic up-slot
reservation withmax_chunks_up4, 20 rounds). Full run in
fs_pool-tests.txt. - Stress:
cio-test-fs_pool0 failures / 3000 runs. - ASan/UBSan build of
fs_pool: clean; TSan (-fsanitize=thread): clean. - Valgrind
--leak-check=full: 0 definitely/indirectly lost, 0 errors
(seevalgrind-summary.txt). - Full matrix (clang 18, UBSan full ctest,
-Wall -Wextra, ASan caveat):
thread-safety-notes.md.
Notes
- On ext4-stored chunk/log/tail-db paths a residual ~10-30 MB/h remains from
ext4 block metadata churn (ftruncate/WAL writes), independent of this
change; with those paths on XFS the patched profile is near-flat (~2.4 MB/h
with no linear chunk-file component, the same figure as the 5.1.2 VM A/B:
+2.3 vs +533 MB/h). - The option is per chunkio context (all filesystem streams), default 0
(disabled), clamped to 4096.
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definitely lost: 0 bytes in 0 blocks |
Stress and sanitizer resultsRun 2026-10-13 against the review-hardened tree (20
Note: the chunkio fs tests use the fixed directory |
Windows (MSVC) test resultsHost: Windows Server 2022, Visual Studio 2022 Build Tools (MSVC x64), All chunkio suites pass (exit codes):
The counter-balance test asserts the loaded-chunk state around delete-by-name, |
📝 Walkthrough
Merge Risk: 🔵 Low · up to
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| Check name | Status | Explanation | Resolution |
|---|---|---|---|
| Docstring Coverage |  |
Docstring coverage is 43.59% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 78 functions across 17 files. (3 skipped:… | Write docstrings for the functions missing them to satisfy the coverage threshold. |
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Check name Status Explanation Description Check Check skipped - CodeRabbit’s high-level summary is enabled. Title check The title clearly and concisely describes the main change: an optional chunk file-slot pool that bounds filesystem slab growth. Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request.
Full details: Docstring Coverage
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Explanation
Docstring coverage is 43.59% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 78 functions across 17 files. (3 skipped: 3 unsupported.)
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Test pool_slot_name_parse... |
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- 🪄 Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @lib/chunkio/src/cio_stream.c:
- Around line 491-494: In cio_stream_delete, move the pool_busy bitmap reset to
the successful stream-removal path, after recursive deletion, and perform it
under pool_lock with pool_unlock. Guard the reset with an explicit ret == 0
check so failed removal leaves the slot bits unchanged.
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📒 Files selected for processing (20)
include/fluent-bit/flb_config.hlib/chunkio/CMakeLists.txtlib/chunkio/include/chunkio/chunkio.hlib/chunkio/include/chunkio/cio_chunk.hlib/chunkio/include/chunkio/cio_file.hlib/chunkio/include/chunkio/cio_file_native.hlib/chunkio/include/chunkio/cio_stream.hlib/chunkio/src/CMakeLists.txtlib/chunkio/src/chunkio.clib/chunkio/src/cio_chunk.clib/chunkio/src/cio_file.clib/chunkio/src/cio_file_unix.clib/chunkio/src/cio_file_win32.clib/chunkio/src/cio_scan.clib/chunkio/src/cio_stream.clib/chunkio/tests/CMakeLists.txtlib/chunkio/tests/fs_pool.csrc/flb_config.csrc/flb_input_chunk.csrc/flb_storage.c
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| /* the stream directory is wiped below: all slots become free */ | ||
| if (st->pool_busy) { | ||
| memset(st->pool_busy, 0, (st->pool_size + 7) / 8); | ||
| } |
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🗄️ Data Integrity & Integration | 🟡 Minor | ⚡ Quick win
🔎 Supported by static analysis
🏁 Script executed:
sed -n '474,530p' lib/chunkio/src/cio_stream.c
sed -n '175,210p' lib/chunkio/src/cio_utils.cRepository: fluent/fluent-bit
Length of output: 2196
Clear pool_busy only after successful stream removal.
cio_stream_delete currently clears the bitmap before cio_utils_recursive_delete. If chunk truncation fails and recursive deletion also fails, the slot file can remain while its bit is free. Move the clear into the successful-removal path and protect it with pool_lock.
The proposed placement before return ret is safe because the ret == -1 branch returns earlier. Add the explicit success check to make that condition clear.
Suggested fix
- /* the stream directory is wiped below: all slots become free */
- if (st->pool_busy) {
- memset(st->pool_busy, 0, (st->pool_size + 7) / 8);
- }
-
#ifdef CIO_HAVE_BACKEND_FILESYSTEM
@@
}
free(path);
+ if (ret == 0 && st->pool_busy) {
+ pool_lock((cio_pool_lock_t *) st->pool_lock);
+ memset(st->pool_busy, 0, (st->pool_size + 7) / 8);
+ pool_unlock((cio_pool_lock_t *) st->pool_lock);
+ }
+
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Review comment at @lib/chunkio/src/cio_stream.c around lines 491 - 494:
In cio_stream_delete, move the pool_busy bitmap reset to the successful
stream-removal path, after recursive deletion, and perform it under pool_lock
with pool_unlock. Guard the reset with an explicit ret == 0 check so failed
removal leaves the slot bits unchanged.
After applying the fix, consider running `coderabbit review --agent` for local
review. Visit https://docs.coderabbit.ai/cli?utm_source=ghpr
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| if (cf->pool_slot >= 0) { | ||
| cio_stream_pool_release(st, cf->pool_slot); |
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With storage.file_pool_size enabled, if a restart scans an in-range slot that is partially written or irrecoverable while the default storage.delete_irrecoverable_chunks is off, cio_file_open() marks the slot busy but this mmap-failure path releases it without clearing the file. If it is the lowest free slot (notably slot 0), every subsequent live chunk reacquires the same corrupt file and returns CIO_CORRUPTED again instead of trying another/fallback slot, stopping ingestion for that stream; keep the failed existing slot busy or truncate it before release.
AGENTS.md reference: AGENTS.md:L282-L284
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| cio_stream_pool_slot_name(slot, slot_name, sizeof(slot_name)); | ||
| free(path); | ||
| path = cio_file_native_compose_path(ctx->options.root_path, | ||
| st->name, slot_name); |
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After a pooled filesystem backlog survives a restart, this replaces the generated logical pid-seconds.nsecs.flb identity with only slot-NNNNNN.flb on disk; cio_scan_stream_files() then reconstructs ch->name from that slot filename, while flb_storage_create() sorts recovered chunks with sort_chunk_cmp(), whose ordering comes from ch->name (src/flb_storage.c:414-466,738-739). Once a low slot has been freed and reused for a newer chunk while an older higher slot remains, the original creation order is unavailable and the newer chunk can be queued first, so persist a sortable logical identity or ordering key across recovery.
AGENTS.md reference: AGENTS.md:L282-L284
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| slot = cio_stream_pool_slot_from_name(ch->name); | ||
| if (slot >= 0) { | ||
| cio_stream_pool_mark_busy(st, slot); | ||
| pool_slot = slot; |
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When pooling is enabled and a caller opens a valid logical chunk name such as slot-000000.flb while slot 0 is already assigned to another live chunk, this branch bypasses cio_stream_pool_acquire() and merely sets an already-set busy bit, so both chunk objects open and mmap the same file; either writer or a close-with-delete can mutate or truncate the other chunk's data. Treat canonical slot names as physical only while st->scanning, or reject that namespace for normal opens.
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| buf[0] = '\0'; | ||
| return; | ||
| } | ||
| snprintf(buf, len, CIO_FILE_POOL_PREFIX "%06d.flb", slot); |
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When a ChunkIO client opts into pooling but uses valid non-.flb chunk names and later calls the existing cio_load(ctx, ".out") API, all pooled chunks are silently skipped: this hard-codes every physical slot to .flb, and cio_scan_stream_files() applies the requested suffix at lines 92-103 before recognizing slots. Stock behavior retained the caller's suffix, so preserve the logical extension or make pooled slots participate correctly in extension-filtered recovery.
AGENTS.md reference: AGENTS.md:L282-L284
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Is my input required here? The "things" above can be improved. |
Depends on fluent/chunkio#117.
Commit 1 mirrors fluent/chunkio#117; the library change is reviewed there.
Summary
With
storage.type: filesystem, chunkio creates a new chunk file per flushper stream and unlinks it after delivery. Each create allocates a dentry+inode
in the kernel and the unlink leaves the objects cached, so on cgroup v2 the
container's charged memory (
memory.stat: slab_reclaimable) grows linearly withflush count until the pod limit is reached. Reported in #12504 and #11958 (see
also #7732 for cgroup v1).
This PR adds an optional, bounded file-slot pool for filesystem streams:
[SERVICE] storage.file_pool_size <n>- default0(disabled / stockbehaviour), clamped to 4096 slots per stream.
slot-NNNNNN.flb); a delivered chunk istruncated and returned to the pool instead of being unlinked, so the same
kernel objects are reused and the file-churn component is removed (on XFS the
slope drops from ~17.4 to ~2.4 MB/h; the residual is unrelated filesystem
metadata, 10-30 MB/h on ext4).
cio_load()a non-slotfile is recovered in place under its own name (unlinked on delete); slot files
are recovered by name; empty slots are skipped; corrupt slots are truncated
and reused.
behaviour, durability preserved).
slot-<6 digits>.flbform is treatedas a slot; near-miss names stay regular files.
succeeded (a failed truncate keeps the slot busy, so stale content is never
handed to a new chunk).
are removed during the scan, and non-empty ones are recovered and unlinked
when delivered.
frees the slot (only pooled chunks are closed this way; with the pool
disabled the previous delete-file-only semantics are kept).
DeleteFileAcannot unlink a file that is still open, sodeleting a loaded non-pooled chunk by name removes its file only after the
chunk is closed; the chunk object itself is never freed by this call.
cio_chunk_counter_*), with an atomic reservationfor new "up" chunks so the
max_chunks_uplimit cannot be exceeded underconcurrency, and an atomic getter for readers. The reservation is taken
before the file is opened and released on every open/map error path; a
non-enforced bring-up (
cio_chunk_up_force) accounts for its chunk onsuccess.
suite passes on MSVC (see below).
Addresses #12504 (continuation of #11958).
Testing
chunkioctest: 6/6 suites pass;fs_pool: 20/20 tests - name parsing(strict), disabled legacy, bounded reuse, overflow fallback, slot/legacy
recovery, corrupt slot, option clamp/invalid, single slot, memory-stream
isolation, delete-by-name, counter balance (limit, failed open, pool-disabled
delete), failed-truncate handling, shrunk-pool cleanup, crash recovery
(after-truncate, mid-write) and threaded use including concurrent
max_chunks_upsaturation. ASan/UBSan clean, ThreadSanitizer clean, Valgrind0 errors / 0 lost, and
fs_poolpasses 3000/3000 stress runs.Windows (MSVC 2022, x64): all chunkio suites pass (
fs_pool17/17 - the fourPOSIX-only tests are excluded; the Win32-threaded
pool_threaded_max_chunks_wincovers the
_InterlockedCompareExchange64reservation path; memfs 0 failuresin 30 runs).
Integration (100-stream tail at 15 MB/s -> filesystem chunks -> null,
storage.max_chunks_up: 32, storage on XFS):slab_reclaimableslopeslot-*.flb, reusedRestart with a 36-chunk backlog written by a stock build: 0
could not retrieve chunk tagerrors, all chunks recovered and delivered;restarting without the option also recovers the slot files normally.
Documentation
The Buffering & Storage docs need the new
storage.file_pool_sizeoption(default 0). I can open the docs PR in
fluent-bit-docsonce the direction isaccepted.
Backporting
(Opt-in change; maintainers to decide.)
Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.
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