[pingqiu]

Fixes #2374.

What

cuObject refuses one cuMemObjGetDescriptor() of CUOBJ_MAX_MEMORY_REG_SIZE or more (4 GiB in cuObject 13.2, 4 GiB - 64 KiB in 13.4), so the generic accelerated engine could not register a buffer that large. SharedCuObjClient::registerBuffer() now registers such a buffer as consecutive 2 GiB pieces:

• Each piece is an ordinary entry in the registration map, so getToken() mints a token against the piece that holds the range, as for any other registration (OBJ: mint cuObject RDMA tokens from the registration base + offset #2369).
• If a piece fails to register, the pieces already registered are released.
• deregisterBuffer() releases every piece of a buffer registered this way.
• A range that crosses a piece boundary gets no token, and the log says why.
• Buffers below the limit are registered exactly as before. The threshold is the header's constant, so it follows the installed cuObject.
• The Dell engine keeps its own size check and is unchanged.

The piece arithmetic is a dependency-free helper in rdma_protocol.h.

Limitation

A single transfer must lie inside one 2 GiB piece. Callers whose pages are no larger than their alignment, with that alignment a power of two up to 2 GiB from the start of the arena, never cross a boundary. For example, LMCache's MP server with --l1-align-bytes 64M (as we ran it) does not cross one. A crossing range fails with NIXL_ERR_BACKEND and does not write anything.

Tests

• Unit: 4 new RdmaProtocol.RegistrationPieces* tests.
• Plugin: AccelLargeRegistrationXferTest and AccelVramLargeRegistrationXferTest register 5 GiB of DRAM or VRAM, transfer 1 MiB ranges in two pieces (one beyond 4 GiB), and check that a range across a piece boundary is rejected. Like the other accel tests, they skip without NIXL_OBJ_ENDPOINT_OVERRIDE.

Measured on an A100 40 GB with a ConnectX-6 Dx VF (RoCE v2), against an S3 endpoint implementing x-amz-rdma-*. The cuObject and cuFile libraries each run loaded were checked in /proc/self/maps.

	main a88b4dd	this PR
ObjAccelTests/*, cuObject 13.4	8/8 pass	10/10 pass (incl. the 2 new, DRAM and VRAM 5 GiB)
Unit tests	the same 4 tests fail in both runs	same 4, plus the 4 new ones pass
5 GiB DRAM registration, write at +4.5 GiB, read into +1 GiB (Python bindings), cuObject 13.2	cuMemObjGetDescriptor failed rc=1, NIXL_ERR_BACKEND	pass, bytes equal
same, cuObject 13.4	—	pass, bytes equal
28 MiB write across the 2 GiB piece boundary	—	rejected cleanly, no object written
sub-range and VRAM cases of #2369 (13.2 and 13.4)	not rerun	pass

The 4 failing unit tests (objCrtTestFixture.TransferBelowThreshold, objDellTestFixture.DellEngineZeroSizePrep, two singleAgentSessionFixture tests) fail identically on unmodified main in this environment, and the unit binary stops at the same test in both runs.

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Summary by CodeRabbit

• New Features
  • Large buffers can be registered in consecutive pieces, enabling RDMA transfers beyond the single-registration size limit.
  • Transfers within a registration piece continue to work, while transfers that cross a piece boundary are rejected.
  • Deregistering a large buffer releases all of its registered pieces.
  • If registration fails partway through, pieces already registered are released.

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📝 Walkthrough

Walkthrough

Buffers at or above the cuObject registration limit are registered as consecutive 2 GiB pieces. SharedCuObjClient tracks and releases those pieces. Tests cover piece generation and 5 GiB transfers in DRAM and CUDA-enabled VRAM.

Changes

Large buffer registration

Layer / File(s)	Summary
Piece generation and validation src/utils/object/rdma/rdma_protocol.h, test/gtest/unit/obj/rdma_protocol.cpp	registrationPieces returns consecutive address and length pairs. Unit tests cover buffer sizes, registration limits, final-piece lengths, and fallback cases.
Piece registration and token lookup src/utils/object/rdma/cuobj_client.h, src/utils/object/rdma/cuobj_client.cpp	SharedCuObjClient registers large buffers in pieces, releases tracked pieces, and reports when a requested range crosses a piece boundary.
Large-buffer transfer coverage test/gtest/plugins/obj_cuobj_plugin.cpp	DRAM and CUDA-gated VRAM tests exercise 5 GiB buffer transfers, verify neighboring ranges remain zero, and expect a cross-boundary transfer to fail.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: aranadive, harshavardhana

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Merge Risk: ⚪ Minimal · up to b4fe5

Large-buffer transfers within registration pieces are supported, while boundary-crossing transfers are rejected without creating an object. No verified issue currently prevents merging.

Pre-merge checks | 4 | 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 11.76% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 17 functions across 5 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: registering cuObject buffers of 4 GiB or more in pieces.
Description check		The description explains what changed, why the change is needed, the design approach, limitations, linked issue, and test results. The optional How section is effectively covered by the implementation…
Linked Issues check		Issue #2374 requires large DRAM and VRAM registrations despite the cuObject single-registration limit. SharedCuObjClient::registerBuffer() calls registrationPieces() with `CUOBJ_MAX_MEMORY_REG_SIZ…
Out of Scope Changes check		The changed helper, client tracking, documentation, and tests directly support issue #2374. The tests verify the required large-registration and boundary behavior. No unrelated functional change is sh…

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Actionable comments posted: 1

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Inline comments:
Review comments at @test/gtest/plugins/obj_cuobj_plugin.cpp:
- Line 392: Update the boundary-failure assertion around runXfer to require
NIXL_ERR_BACKEND rather than accepting any non-success result, then read the
object and verify its contents remain unchanged after the rejected write.

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📒 Files selected for processing (5)

• src/utils/object/rdma/cuobj_client.cpp
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• src/utils/object/rdma/rdma_protocol.h
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[svc-nixl]

🤖 CI Triage Agent — Clang Format Check · commit e1d0562d

TL;DR: The "Clang Format Check" job failed purely on a style violation — one hand-wrapped addDesc(...) call in test/gtest/plugins/obj_cuobj_plugin.cpp doesn't match the repo's .clang-format; reformat those lines with clang-format-19 and push.

Full analysis

Summary: GitHub Actions job clang-format (run 38107582604) exited 1 because clang-format-diff-19 produced a non-empty diff for lines 393–400 of test/gtest/plugins/obj_cuobj_plugin.cpp.

Root cause: Not an infra or build problem. The workflow runs git diff -U0 HEAD^1 HEAD -- $FILES | clang-format-diff-19 -p1 -style=file, and any suggested reformatting makes the step fail. The repo's .clang-format sets BinPackArguments: false with ColumnLimit: 100 and AlignAfterOpenBracket: Align, so the two arguments to nixlBlobDesc(...) cannot be split across the open paren the way they are hand-written. clang-format wants the whole nixlBlobDesc(...) expression moved onto its own continuation line:

    cross_obj.addDesc(
        nixlBlobDesc(nixlBasicDesc(), "test-obj-key-large-" + std::to_string(xfer_entries.size())));

The current source at lines 396–397 wraps after addDesc(nixlBlobDesc( instead, which is the only delta the checker reported — no other file in the PR's touched set failed.

Implicated commit: [REDACTED:Hex High Entropy String] (PR #2375, branch obj-large-registration) — the commit that introduced the cross_obj / large-registration test block.

File: test/gtest/plugins/obj_cuobj_plugin.cpp:396-397

Suggested fix: Replace lines 396–397 with the clang-format-preferred form above (the exact text the job printed as the "after formatting" side), then re-push. Easiest reliable route locally:

git diff -U0 HEAD^1 HEAD -- test/gtest/plugins/obj_cuobj_plugin.cpp \
  | clang-format-diff-19 -p1 -style=file -i

or clang-format-19 -i -style=file test/gtest/plugins/obj_cuobj_plugin.cpp and keep only the intended hunk. Note the reformatted line lands at exactly 100 columns, so don't re-wrap it by hand afterwards. Installing the repo's pre-commit hook (or running clang-format-19 before pushing) would catch this class of failure locally — note the check pins version 19, so formatting with a different clang-format major version can produce different output.

Related: none

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[ovidiusm]

There's an overlapping stack from @harshavardhana: #2379 → #2380 → #2382. #2382 solves the same large-registration problem with opt-in overlapping windows, so any offset works up to 2 GiB − 64 KiB, at about twice the registration cost. Please coordinate so we land one design.

Also, #2379 changes SharedCuObjClient::registrations_ to reference-counted records so several agents in one process can share a buffer. That fix is needed regardless, this PR's registrations_ and pieced_buffers_ handling would have to be reworked on top of it.

[aranadive]

@pingqiu is this still an issue with CUDA 13.4.2? We had two similar PRs #2382 and this one. #2382 was closed as CUDA 13.4 allowed >4GiB transfers.

[aranadive]

We are tracking S3 RDMA multipart uploads with #2406.

[pingqiu]

@aranadive No, it is not an issue on 13.4. I reran the reproduction from #2374 on unmodified main (9fbfcbb), same host and same probe, against both cuObject versions:

cuObject	one DRAM registration of 5, 16 and 64 GiB	PUT from base + 4.5 GiB, GET into base + 1 GiB
13.2 (libcuobjclient 1.1.1.22)	cuMemObjGetDescriptor failed rc=1 for all three	not reached
13.4 (libcuobjclient 1.3.1.55)	succeeds for all three	pass, bytes equal

My earlier 13.4 runs only covered this branch, not unmodified main, so I had not seen that. Since 13.4 handles large registrations itself, this PR is only useful on 13.2/13.3, and I don't think that is worth a second code path. Closing this, along with #2374.

One note: the 13.4 header still defines CUOBJ_MAX_MEMORY_REG_SIZE as 4 GiB − 64 KiB, although the library accepts 64 GiB.

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