Module expert_tier 

2026-09-25: ExpertTier: fetch one expert record into a slot and return the device addresses of its six sub-buffers, with its scalars. The tiers are PosixTier (read, then copy into a device buffer), UmaArenaTier (read straight into a pinned arena slot) and RdmaTier (expert_tier_rdma.rs, from a peer). It is not a StorageBackend, whose reads take KV group keys.

Owner: metrale-storage experts. Invariants:

• Every tier builds its ExpertResidency with residency_from, which rejects a record whose header names another (layer, expert).

Structs

ArenaSlot

2026-09-25: A destination slot: which slab, and which slot in it.

ExpertResidency

2026-09-25: The six sub-buffer device addresses and the scalars of one fetched expert, each array ordered gate, up, down.

PosixTier

2026-09-25: Read the record into a host buffer (buffered, through ExpertFileReader), copy it into the slot’s part of one device buffer, and sync the stream.

UmaArenaTier

2026-09-25: Read the record straight into a pinned arena slot (O_DIRECT on Linux); the returned addresses point into the arena, and nothing is copied.

Enums

TierKind

Traits

ExpertTier

2026-09-25: Fetch an expert record into a slot and return its residency.

Functions

open_tier

2026-09-25: Open the tier named by backend:

read_device

2026-09-25: Copy len bytes from a device address into a new Vec, then sync the stream.