Module rdma_snapshot 

Offset-addressed RDMA arena for the SSM-snapshot spill tier.

A minimal, synchronous transport over the CX7 verbs + RW-blade paging peer protocol the KV overflow tier uses, but addressed by a flat byte offset (snapshots are keyed by an opaque id → arena slot) rather than the KV GroupKey/group_stride layout — reusing that layout would corrupt live KV (its write_from_host asserts src.len()==group_bytes).

The paging peer is layout-agnostic (client sends total_bytes, the peer registers ONE RW MR and serves base+offset), so a second peer instance on its own port serves the snapshot arena with zero peer-side change. Each op is drained to completion before returning (one blob ~64 MB, ~5–7 ms — the spill/fault path is latency-, not throughput-critical), so the caller’s SnapshotBlobStore::{put,get} contract (durable on return) holds.

Gathering the scattered per-layer SSM state into the contiguous blob and all device-stream ordering already happen in SsmSnapshotPool::{spill_slot, fault_in_slot}; this transport only moves host bytes.

Structs

RdmaSnapshotArena

Placeholder when RDMA verbs / CUDA aren’t built. connect always errors, so crate dependents degrade to the host-RAM tier; write/read are unreachable (a stub arena is never successfully constructed).