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## 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