rdma: track libs3rdma, and fix the size guard's off-by-one - #1565
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libminiocpp's RDMA transport moved from NVIDIA's libcuobjclient to libs3rdma, so the CI that builds it no longer installs librdmacm or libnuma: libs3rdma resolves the RDMA stack itself, at run time. The registration ceiling allowed exactly 4 GiB. The real limit is what one RDMA descriptor can describe, and the descriptor carries the window size in a 32-bit field, so 4 GiB is one byte too many: such a buffer passed this guard and was then declined inside libminiocpp, becoming the silent fallback to a much slower HTTP transfer that the guard exists to prevent. Now 2**32 - 1, and renamed off the cuObject spelling since the bound no longer comes from there. is_rdma_available reports a usable local RDMA device rather than a reachable server: DC is connectionless, so there is no session to probe. A server that will not serve RDMA still declines per request with x-amz-rdma-reply: 501, so the fallback behaviour is unchanged. The path now works on native InfiniBand as well as RoCE, on any HCA, with no NVIDIA client library on the host. GPU buffers are unaffected: the SDK links no CUDA and allocating device memory stays the caller's job. S3RDMA_DEVICE pins a particular HCA on a multi-NIC host.
📝 WalkthroughWalkthroughThe RDMA transfer limit now uses the 32-bit descriptor token maximum. PUT and GET boundary tests reflect the new limit. RDMA documentation and CI setup now describe the ChangesRDMA support updates
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🔵 Low · up to The PR updates the RDMA CI workflow, but it still references checkout through a mutable tag instead of an immutable commit, allowing unexpected action changes to affect CI; the PR is otherwise mergeable with explicit owner awareness or follow-up to pin the action. Possibly related PRs
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In `@minio/rdma.py`:
- Around line 242-245: Update the split guidance in the PUT and GET error
messages near the RDMA size validation to use the inclusive valid limit,
_RDMA_MAX_MEMORY_REG_SIZE, instead of stating parts can be at most 4 GiB; keep
the existing validation and error context unchanged.
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.github/workflows/ci-rdma.ymlCLAUDE.mdREADME.mdminio/rdma.pytests/unit/rdma_test.py
…ance The RDMA jobs built minio-cpp from a floating main and failed to link against -lnuma and -lrdmacm. Those come from the pre-libs3rdma tree: the current one resolves the RDMA stack at runtime through libs3rdma and links nothing else, so pinning the ref fixes the build rather than adding the packages. Pinned to the same commit the other SDKs use. pylint rejected two 86-column lines in the size-guard errors; rewrapped. The same errors told callers to "split into parts <= 4 GiB", which the guard rejects: the limit is 2**32 - 1, one byte short of 4 GiB. Advice that fails when followed is worse than none, so report the byte limit that is actually enforced.
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In @.github/workflows/ci-rdma.yml:
- Line 39: Update the actions/checkout step in the CI workflow to reference the
intended v4 release by its full 40-character commit SHA instead of the mutable
v4 tag.
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libminiocpp's RDMA transport moved from NVIDIA'slibcuobjclienttolibs3rdma(minio/minio-cpp#250). minio-py reaches RDMA through libminiocpp's C API via ctypes, so the binding surface is unchanged — but two things need updating, one of which is a real bug.The off-by-one is a live bug
_CUOBJ_MAX_MEMORY_REG_SIZEwas4 * 1024**3, allowing exactly 4 GiB. The real ceiling is what one RDMA descriptor can describe, and the descriptor carries the window size in a 32-bit field — so 4 GiB is one byte too many.A 4 GiB buffer therefore passed this guard, reached libminiocpp, and was declined there: it fell back to a single ordinary HTTP request, which is precisely the silent slowdown the guard exists to prevent.
Now
2**32 - 1, matchingkRDMAMaxMemoryRegSizein minio-cpp, and renamed to_RDMA_MAX_MEMORY_REG_SIZEsince the bound no longer comes from cuObject. The boundary tests move with it and still assert inclusivity at the limit.Doc correction
is_rdma_availablereported "cuObj is connected to cuObjServer". It now reports a usable local RDMA device: DC is connectionless, so there is no session to probe. A server that will not serve RDMA still declines per request withx-amz-rdma-reply: 501, so fallback behaviour is unchanged — only the meaning of this predicate is.CI
Drops
librdmacm-dev/libnuma-devfrom the apt install —libs3rdmaresolves the RDMA stack itself at run time, so nothing links them.What this buys
Through libminiocpp, the RDMA path now works on native InfiniBand as well as RoCE, on any HCA, with no NVIDIA client library on the host.
GPU buffers are unaffected: the SDK links no CUDA, and allocating device memory stays the application's job — CuPy / PyTorch pointers still work as
data=/into=.S3RDMA_DEVICEpins a particular HCA on a multi-NIC host; README documents it.Verification
All 7 RDMA unit tests pass, including the boundary tests at the new limit.
Requires minio/minio-cpp#250.
Summary by CodeRabbit
Bug Fixes
Documentation