processfork-vllm 1.0.0

ProcessFork plugin for vLLM ≥0.10 — paged-KV-cache snapshot/restore via batch-invariant kernels.

processfork-vllm

ProcessFork plugin for vLLM ≥0.10. Adds OpenAI-compatible extended endpoints for snapshot / fork / checkout that walk vLLM's paged KV cache via the batch-invariant kernel mode.

Install

pip install "processfork-vllm[vllm]"

Use

vllm serve meta-llama/Llama-3-8B \
  --enforce-deterministic \
  --plugin processfork

Then:

POST /v1/processfork/snapshot       { "name": "..." }
  → { "cid": "sha256:..." }

POST /v1/processfork/fork           { "cid": "...", "n": 12 }
  → { "cids": ["sha256:..."] }

POST /v1/processfork/checkout       { "cid": "..." }
  → { "ok": true }

Bit-exact restore requires --enforce-deterministic (stable since vLLM 0.10). Without it, restore produces logits within ≤1e-4 of the originals.

The wire format matches agent_docs/cache-layer.md — paged-batchinvariant-v1. K and V pages are content-addressed independently so a fork that mutates only V (one-token decode) shares its K page with siblings.

Status

The trait surface and the paged-batchinvariant-v1 wire format are stable. The live FFI shim into vllm.worker.cache_engine lands in v1.0.1. Until then, the plugin's HTTP surface returns 501 Not Implemented with a clear pointer to this README.