Module kv_paging 

KV as a first-class paging kind (part of the tiered-cache consolidation, DEFAULT-OFF behind ATLAS_KV_PAGING).

The flag-OFF KV overflow tier (rdma_kv_backend) takes the “dumb one-sided path”: the peer registers ONE RW MR and the CLIENT owns a static allocator (base + group_id × group_stride) over a fixed arena — no peer residency, no NVMe spill. It selects that mode with the v2 header’s blob_bytes == 0 RAW sentinel (the bare [u64 total_bytes] handshake is retired). This module is the alternative client: it sends the paging handshake (PAGING_MAGIC_V2, kind = PagingKind::KV) so KV inherits what the SSM snapshot tier already has — peer-owned residency, an NVMe-backed cold tier (unbounded depth with --swap-cap-gb-kv 0), and peer capacity pooling. The peer side is ALREADY wired: the (kind, blob_bytes) arena registry accepts kind 1 and --swap-cap-gb-kv parses; the whole feature is this client.

Layout: the paging RECORD is one whole KV block (GroupLayout:: block_bytes() = 2·num_kv_heads·group_stride) — exactly the fixed-size record atlas_tier::Residency demands, one contiguous blob at one pointer on both ends, and 1 control RTT per block instead of 2·num_kv_heads. Keys fold the per-model fingerprint + full layout identity + a per-client salt (see ns); PagingKind::KV in the handshake plus the ns::KV_DOMAIN fold domain-separate KV from SSM.

FLAG OFF (ATLAS_KV_PAGING unset/0) the selection helper returns the raw one-sided RdmaKvBackend — identical data plane (v2 RAW handshake since the v2 handshake), so any regression bisects on this single flag.

Modules

ns

KV paging namespace + wire-key derivation (ATLAS_KV_PAGING, part of the tiered-cache consolidation).

Functions

kv_miss_error

The hard-error a KV paging GET miss maps to. StorageBackend::read has no miss channel and an evicted KV block is UNRECOVERABLE without recomputing the prefix (unlike SSM snapshots, which recompute on miss by design) — so ST_MISS is corruption-equivalent and must fail loudly, naming the peer config that makes the KV kind miss-proof.