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[EPLB] Share the NIXL agent with the replacement communicator (simplification for #63134) - #1
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stefankoncarevic merged 1 commit intoOct 23, 2026
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Replace the per-arena agent registry with passing the previous communicator's NixlWrapper to the new one. Expert weights and expert_buffer keep their storage across reconfigurations, so the shared agent's registrations stay valid; Python refcounting decides when the agent dies and NIXL deregisters/disconnects in its destructor. Re-adding a known peer's metadata is idempotent in NIXL, so no remote-agent cache is needed either. Signed-off-by: NickLucche <nicolo.lucchesi@mistral.ai>
stefankoncarevic
merged commit Oct 23, 2026
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stefankoncarevic:elastic-ep-scaling-mi355
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Suggested simplification for vllm-project#63134. It keeps the fix (one NIXL agent per worker, no second registration of the same pages) without the arena registry.
What changes
NixlWrapper(EplbState.create_communicator→create_eplb_communicator(prev_communicator=...)). It registers memory only when it creates a fresh agent._ArenaAgent,_ARENA_AGENTS, the(device, lo, hi)key, the user count,covers()/registered_rangesand theremote_namescache are all removed.__del__only releases transfer handles. The agent is dropped when the last communicator referencing it is collected, and its destructor deregisters memory and disconnects peers (~nixlLocalSection→deregisterMem).Why this is enough (NIXL behavior)
expert_bufferkeep their storage across elastic EP reconfigurations, sincenum_local_expertsis fixed. So the existing registrations stay valid.add_remote_agentfor an already known peer is idempotent:loadRemoteMDmerges into the existing entry, andloadConnInfois a no-op when the conn info is unchanged. There is never a duplicate entry to guard against.Net change is about −100 lines. The
__del__shutdown guard and the CI changes from the original PR are untouched.Not tested on GPU from my side; it would be great if you could rerun the MI355 / H100 elastic EP steps with this.