- Removes the GTest dependency, replacing it with a minimal custom
framework (`test/framework.*`) that covers only what the tests actually
use — a unified `TEST()` macro with SFINAE-based fixture auto-detection,
`EXPECT_*`/`ASSERT_*` assertions, environments, and setup/teardown.
- `--exclude-perf-tests` flag and substring-based negative filtering
- `MSCCLPP_ENABLE_COVERAGE` CMake option with gcov/lcov; CI uploads to
Codecov
- Merges standalone `test/perf/` into main test targets
- Refactors Azure pipelines to reduce redundancies & make more readable
---------
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Changho Hwang <changhohwang@microsoft.com>
## Summary
Fix a use-after-free where the CUDA allocation handle
(`CUmemGenericAllocationHandle`) was released prematurely while the
exported fabric handle still referenced it.
## Problem
Unlike POSIX FD handles (where the kernel keeps the allocation alive via
the open file descriptor), fabric handles do not hold their own
reference to the underlying allocation. The original code called
`cuMemRelease(allocHandle)` immediately after exporting the fabric
handle, freeing the allocation. When a remote process later tries to
`cuMemImportFromShareableHandle` using that fabric handle, it references
a freed allocation — a **use-after-free**.
This affected both code paths:
1. **`GpuIpcMemHandle::create()`**: The local `allocHandle` obtained via
`cuMemRetainAllocationHandle` was released right after fabric export,
leaving the fabric handle dangling.
2. **`GpuIpcMemHandle::createMulticast()`**: The `allocHandle` from
`cuMulticastCreate` was unconditionally released, even when it was the
only thing keeping the multicast object alive for the fabric handle.
## Fix
- **Added `allocHandle` field** to the `fabric` struct in
`GpuIpcMemHandle` to store the allocation handle and keep it alive for
the lifetime of the `GpuIpcMemHandle`.
- **`create()`**: Retain an additional reference via
`cuMemRetainAllocationHandle` and store it in `fabric.allocHandle` when
a fabric handle is successfully exported.
- **`createMulticast()`**: Store the `allocHandle` directly in
`fabric.allocHandle` instead of unconditionally releasing it. Only
release if fabric export was not used.
- **`deleter()`**: Release `fabric.allocHandle` via `cuMemRelease` when
the handle type includes `Fabric`, ensuring proper cleanup.
- **`GpuIpcMem` constructor (importer side)**: Clear
`fabric.allocHandle` after importing, since the importer gets its own
handle via `cuMemImportFromShareableHandle` and should not release the
exporter's allocation handle.
## Files Changed
- `src/core/include/gpu_ipc_mem.hpp` — Added
`CUmemGenericAllocationHandle allocHandle` to fabric struct.
- `src/core/gpu_ipc_mem.cc` — Retain/release allocation handle properly
across create, createMulticast, deleter, and importer paths.
## Summary
This PR addresses a multicast resource leak, fixes `cuMemMap` offset
handling for multicast handles, renames NVLS allreduce algorithm classes
for clarity, and adds a new unit test for `SwitchChannel`.
### Bug Fixes
#### 1. Fix multicast allocation handle leak in `createMulticast()`
(`gpu_ipc_mem.cc`)
`GpuIpcMemHandle::createMulticast()` called
`cuMulticastCreate(&allocHandle, ...)` but never released the local
`allocHandle` after exporting it to shareable handles (POSIX FD /
Fabric). This caused a reference count leak — the multicast object was
never freed even after all mappings and imported handles were released.
Per the [CUDA Driver API docs for
`cuMemRelease`](https://docs.nvidia.com/cuda/cuda-driver-api/group__CUDA__VA.html):
> *"The memory allocation will be freed when all outstanding mappings to
the memory are unmapped and when all outstanding references to the
handle (including its shareable counterparts) are also released."*
The fix adds `cuMemRelease(allocHandle)` after export, matching the
existing pattern used for regular allocations in
`GpuIpcMemHandle::create()`.
**Impact:** Without this fix, repeated creation/destruction of NVLS
connections causes OOM after ~120 iterations when allocating 1GB
multicast buffers on H100.
#### 2. Fix `cuMemMap` offset for multicast handles (`gpu_ipc_mem.cc`)
`cuMemMap` requires `offset=0` for multicast handles. Previously, the
code attempted to map at a non-zero offset within the multicast object,
leading to errors when binding multiple buffers to the same
`NvlsConnection`. The fix maps the entire range `[0, mcOffset +
bufferSize)` and returns the pointer offset by `mcOffset`. This only
consumes extra virtual address space; no additional physical memory is
used.
### Refactoring
#### 3. Rename NVLS allreduce algorithm classes
Renamed for clarity:
- `AllreduceNvls` → `AllreduceNvlsZeroCopy`
- `AllreduceNvlsWithCopy` → `AllreduceNvlsWarpPipeline`
- `AllreduceNvlsWithCopy2` → `AllreduceNvlsBlockPipeline`
Updated all references in builder, selector, docs, and examples.
#### 4. Move `nvlsConnections` setup to `initialize()`
Moved `nvlsConnections_` from `AlgorithmCtx` (which no longer has this
member) to individual algorithm class members, initialized in their
`initialize()` methods.
### Tests
#### 5. Add `TwoChannelsSameConnection` test
New unit test that creates two `SwitchChannel` instances from the same
`NvlsConnection`, performs reduce operations on both, and verifies
correctness. This exercises the multi-bind path that triggered the
`cuMemMap` offset fix.
### Files Changed
- `src/core/gpu_ipc_mem.cc` — multicast handle leak fix + cuMemMap
offset fix
- `src/ext/collectives/allreduce/allreduce_nvls_zero_copy.cu` (renamed)
- `src/ext/collectives/allreduce/allreduce_nvls_warp_pipeline.cu`
(renamed)
- `src/ext/collectives/allreduce/allreduce_nvls_block_pipeline.cu`
(renamed)
- `src/ext/collectives/allreduce/allreduce_nvls_packet.cu` —
nvlsConnections fix
- `src/ext/collectives/include/allreduce/*.hpp` — renamed headers
- `src/ext/collectives/algorithm_collection_builder.cc` — updated
references
- `src/ext/nccl/algorithm_selector.cc` — updated algorithm names
- `test/mp_unit/switch_channel_tests.cu` — new test
- `docs/guide/mscclpp-torch-integration.md` — updated names
- `examples/torch-integration/customized_comm_with_default_algo.py` —
updated names
## Summary
Fix NCCL fallback communicator cleanup errors and update CI to use
stable NCCL releases.
## Problem
When using `LD_PRELOAD=libmscclpp_nccl.so` with NCCL fallback enabled,
the following warnings appear at program exit:
```
NCCL WARN commReclaim: cleanup comm 0x55a0dcadaa90 rank 3 failed in destroy/abort, error 3
```
This is caused by three bugs in the NCCL fallback communicator lifecycle
management.
## Root Causes & Fixes
### 1. Symbol interposition during NCCL cleanup (`RTLD_DEEPBIND`)
**Root cause:** When the fallback NCCL library is loaded via `dlopen`,
its internal calls to its own public API functions (e.g.,
`ncclCommWindowDeregister`, `ncclMemFree`) during `commFree` cleanup are
intercepted by our `LD_PRELOAD`'d stub functions, which return errors.
This causes NCCL's `commReclaim` to report `error 3`
(`ncclSystemError`).
**Fix:** Add `RTLD_DEEPBIND` to the `dlopen` flags. This makes the
dlopen'd NCCL library resolve its own symbols internally first,
bypassing our interposition layer for internal calls.
### 2. Missing `ncclCommFinalize` forwarding
**Root cause:** `CommFinalize` was not in the `mscclppNcclOps_t` struct
and was never loaded via `dlsym`. So `ncclCommFinalize` never forwarded
to the real NCCL's finalize, which is required before `ncclCommDestroy`
in NCCL 2.29+.
**Fix:** Add `CommFinalize` to the ops struct and load it via `dlsym`.
Forward the call in `ncclCommFinalize`.
### 3. CI: Use latest NCCL release tag
The CI pipeline was cloning the NCCL default branch (which may contain
unreleased/unstable code). Updated to fetch the latest release tag via
GitHub API and clone that specific tag.
## Testing
Verified with the exact CI command:
```bash
mpirun -np 8 --bind-to numa --allow-run-as-root \
-x LD_PRELOAD=libmscclpp_nccl.so \
-x MSCCLPP_ENABLE_NCCL_FALLBACK=TRUE \
-x MSCCLPP_FORCE_NCCL_FALLBACK_OPERATION="allreduce" \
-x MSCCLPP_NCCL_LIB_PATH=/root/nccl/build/lib/libnccl.so \
all_reduce_perf -b 1K -e 1G -f 2 -d half -G 1 -w 10 -n 100
```
- **Before:** `commReclaim: error 3` warnings on all 8 ranks at exit
- **After:** Clean exit, no warnings, correct results
## Files Changed
- `src/ext/nccl/nccl.cc` — Fix comm destroy lifecycle (RTLD_DEEPBIND,
CommFinalize forwarding, destroy order)
- `.azure-pipelines/templates/nccl-test.yaml` — Use latest NCCL release
tag in CI
I recently encountered a weird memory usage issue.
After starting the proxy service on a cuda device X > 0, I notice an
unexpected thread entity apprear on both the GPU X and GPU 0, where GPU
0's share is about 500MB. Note that when the device is 0, there is no
extra memory usage.
The image clearly shows that when 8 ranks each using one GPU and
starting proxies, the GPU 0 sees 7 extra threads, each consuming 500MB
extra memory.
<img width="1247" height="1367" alt="Screenshot 2026-02-28 000153"
src="https://github.com/user-attachments/assets/cfd0d47f-319b-4ebb-bf19-dec66062e6f4"
/>
After tracking down to when it happens, I identified the root cause in
Proxy thread initialization.
// never capture in a proxy thread
auto mode = cudaStreamCaptureModeRelaxed;
MSCCLPP_CUDATHROW(cudaThreadExchangeStreamCaptureMode(&mode));
pimpl_->threadInit();
The call to cudaThreadExchangeStreamCaptureMode() actually triggers some
resource allocation on the "current device" which is still 0 for the
starting thread.
The later threadInit() is too late to set the correct GPU number.
The fix is simple: call threadInit() before the first cuda call:
pimpl_->threadInit();
// never capture in a proxy thread
auto mode = cudaStreamCaptureModeRelaxed;
MSCCLPP_CUDATHROW(cudaThreadExchangeStreamCaptureMode(&mode));
This guarantees that the current device is properly set before calling
any resource-allocating cuda functions.
This is the memory usage after the fix. The extra memory usages are
gone.
<img width="1242" height="459" alt="Image (1)"
src="https://github.com/user-attachments/assets/4256e4c8-6f1d-4844-9f77-5b2935387df9"
/>
---------
Co-authored-by: Binyang Li <binyli@microsoft.com>
