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added 2 commits
October 20, 2026 00:13
The writable layer's datafile now honors the global ioEngine so it can use libaio (O_DIRECT, wrapped in a 4K aligned adaptor) instead of always going through psync. turboOCI target/gzip files and posixaio fall back to psync. LSMT appends use positioned writes so the aligned adaptor stays in the I/O path, and both TCMU and ublk photon envs init libaio. Signed-off-by: Yifan Yuan <tuji.yyf@outlook.com>
Each ublk queue caches a fixed 32 photon I/O threads; with a deeper queue every I/O beyond that creates and destroys its own thread. Expose the size as ublkThreadPoolSize in overlaybd.json, default 32. Signed-off-by: Yifan Yuan <tuji.yyf@outlook.com>
BigVan
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liulanzheng
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a balanced review from Copilot
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Copilot
October 19, 2026 16:16
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🔵 Needs a closer look
Direct-I/O opening needs correction, and alignment-sensitive sealing needs regression validation before human approval.
1 open issue
What changed in this PR
This PR makes ublk queue thread caching configurable and extends configured I/O-engine support to writable upper data files.
Changes:
- Adds
ublkThreadPoolSize, defaulting to 32, with configuration documentation. - Enables libaio initialization and aligned upper-file I/O.
- Updates positioned LSMT writes and adds upper-engine regression tests.
| File | Description |
|---|---|
| src/ublk/ublk_device.cpp | Configures queue thread pools and initializes libaio. |
| src/test/image_service_test.cpp | Tests upper-file engines, concurrent writes, and reopening. |
| src/overlaybd/lsmt/file.cpp | Uses positioned writes for data, indexes, and trailers. |
| src/main.cpp | Enables libaio in shared I/O workers. |
| src/image_file.cpp | Selects upper-file engines and adds alignment handling. |
| src/example_config/overlaybd.json | Adds the thread-pool setting. |
| src/config.h | Defines the setting and default. |
| README.md | Documents per-queue thread caching. |
Review effort: Balanced
| auto engine = image_service.global_conf.ioEngine(); | ||
| if (!upper.target().empty() || engine == ioengine_posixaio) | ||
| engine = ioengine_psync; | ||
| data_file = open_localfile_adaptor(upper.data().c_str(), O_RDWR, 0644, engine); |
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