[KV Offload] Reject secondary tiers on engines that span nodes by javieratomic · Pull Request #62930 · vllm-project/vllm

javieratomic · 2026-10-21T15:37:17Z

Overview

This PR makes TieringOffloadingSpec fail at startup, instead of serving wrong KV, when secondary tiers run on an engine whose workers span several nodes (#54415).

It applies to main on its own and depends on no other PR. #62933 builds on it to support the multiprocessing executor with --nnodes > 1.

Claims

With secondary tiers and more than one worker, every worker checks at creation whether the engine's workers share a node, and raises NotImplementedError if they do not. This covers every way to place workers on several nodes (mp with --nnodes, Ray, external_launcher) without looking at the executor.
Single-node engines, single-worker engines and engines without secondary tiers are unchanged.

Validation

Multi-node startup on 2× DGX Spark (GB10), vllm/vllm-openai:nightly-00b6c4c565 with this branch's changed Python files on top, TP=2, mp executor with --nnodes 2, facebook/opt-125m:

TieringOffloadingSpec with an fs tier: both workers fail at startup with NotImplementedError: TieringOffloadingSpec secondary tiers are not supported on engines whose workers span several nodes.
TieringOffloadingSpec without secondary tiers: starts and serves; the same prompt sent twice gives the same output.

Unit test: tests/v1/kv_offload/test_factory.py::test_tiering_spec_rejects_secondary_tiers_across_nodes fakes the TP, PP and PCP groups and in_the_same_node_as(): it rejects a TP, PP or PCP group that spans nodes, accepts groups that each share a node, queries all three groups even after one spans nodes, and queries none without secondary tiers. Without the fix, four of its five cases fail. CI provides one host only, so it cannot run a real multi-node rejection.

Suites (CPU-only container):

pytest tests/v1/kv_offload/tiering tests/v1/kv_offload/test_factory.py \
  tests/v1/kv_offload/test_file_mapper.py \
  tests/v1/kv_connector/unit/offloading_connector
# 1286 passed, 1 failed (on 71294c2e9a)

The one failure, test_worker.py::test_register_packed_kv_caches_skips_scratch_group, needs a GPU and fails the same way on main; it passes on GPU.

ruff check and ruff format --check pass on the changed files.

Details

Root cause. The tiering scheduler and its secondary tiers run in the engine core and address only its node's /dev/shm region. Since #58497 every worker writes the slot of its rank, but workers on other nodes write it into their own node's region. Secondary tiers therefore persist rows without those slots, and promotions never fill them.

Detection. An engine's workers form a grid of its TP, PP and PCP groups (DCP lives inside TP), so they all share one node exactly when each of those groups does. create_worker() therefore calls in_the_same_node_as() on each group with more than one rank. It is a collective over that group, which every worker of the group reaches during KV cache registration. Every rank runs all three before any of them raises, so a rank whose own TP group spans nodes cannot leave the ranks of a node-local TP group waiting in the PP or PCP collective. It runs only with secondary tiers, since without them each node's region serves its own workers.

Not a duplicate. Searched open PRs for "54415 in:body", "multi-node offload", "secondary tiers nodes", "local_world_size offload" and "shared region node". #53474 also sizes node-local regions and rejects multi-node secondary tiers from the config; #46556 moves rank-local shards to a shared filesystem through worker transfers instead; #62058 and #53073 deal with /dev/shm capacity and region lifecycle, not with nodes.

Docs: docs/features/kv_offloading_usage.md states the restriction.

AI assistance. AI assistance (Claude) was used to write this change, its tests and this description. I reviewed every changed line and ran the tests above.

Pull Request Checklist

I used vLLM's /pr-checklist skill. (Mandatory for agents, optional for humans).
AI assistance was used during the creation of this PR.
Design Fit: Minimizes impact on core components, reuses existing functionality, and justifies added complexity.
Testing and Validation: Validates the change and ensures any added tests are meaningful and reliable, with CI coverage or documented CI resource constraints and validation performed outside CI.
Code Quality and Style: Keeps code and comments clear and concise, and updates relevant documentation and examples.
Pull Request Contents: Includes a brief summary and relevant links, supports claims with evidence, explains root causes and implementation trade-offs, and follows the contributing guide.

🤖 Generated with Claude Code

Depends on vllm-project#52838, vllm-project#62930 and vllm-project#62929. With TieringOffloadingSpec, the scheduler and its secondary tiers run in the engine core next to worker rank 0 and read only that node's /dev/shm region, so workers on other nodes write their slots into a region nobody reads (vllm-project#54415). vllm-project#62930 rejects such engines at startup; this lifts the rejection for the multiprocessing executor with nnodes > 1 by mirroring remote slots into the head region. With secondary tiers and workers on several nodes (mp executor, nnodes > 1): - Each worker off the head node keeps a compact region with only its slot. A background thread pushes the slot of each stored chunk to the head region before the store is reported, and pulls it before a load's DMA. Copies move at most 32 MiB per request; loads go first, and a waiting store runs after at most four load requests. - Transport: a ZMQ ROUTER on worker rank 0 bound to VLLM_HOST_IP. ZAP admits only the remote workers' addresses; requests carry a random per-engine token and a per-client epoch and sequence, so delayed puts are rejected. None of it is cryptographic. - A copy that fails after its retries (mirror_attempts x mirror_timeout_s) is reported through vllm-project#52838: failed_jobs drops a store and failed_recving recomputes a request whose load failed. Before a failed push is reported, a fence makes the head reject its late attempts; if the fence fails, the mirror stops. - Worker creation gathers errors, addresses, the server endpoint and the client handshake from every rank, so a failure raises on all. A remote worker's compact region is unlinked as soon as it is mapped. - FileMapper tiers (fs, obj, p2p) of multi-node engines store under their own slot_layout namespace unless rows are topology-agnostic. - The cache-reset promotion hold of vllm-project#62929 also covers a remote node's late slot push: a remote worker reports a store only after its push, and fences a failed push's late attempts before reporting it. - The rejections of vllm-project#62930 for external_launcher, an unknown node count (Ray), canonical_layout and replicated_layout stay. Without secondary tiers, regions stay node-local as before. Signed-off-by: Javier López <jlopez@semark.com> Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011NBbUxmYzpDb5p1ScTziyw

github-actions · 2026-10-21T15:39:20Z

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mergify · 2026-10-21T15:48:36Z

Documentation preview: https://vllm--62930.org.readthedocs.build/en/62930/

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chatgpt-codex-connector · 2026-10-21T15:56:04Z

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Depends on vllm-project#52838, vllm-project#62930 and vllm-project#62929. With TieringOffloadingSpec, the scheduler and its secondary tiers run in the engine core next to worker rank 0 and read only that node's /dev/shm region, so workers on other nodes write their slots into a region nobody reads (vllm-project#54415). vllm-project#62930 rejects such engines at startup; this lifts the rejection for the multiprocessing executor with nnodes > 1 by mirroring remote slots into the head region. With secondary tiers and workers on several nodes (mp executor, nnodes > 1): - Each worker off the head node keeps a compact region with only its slot. A background thread pushes the slot of each stored chunk to the head region before the store is reported, and pulls it before a load's DMA. Copies move at most 32 MiB per request; loads go first, and a waiting store runs after at most four load requests. - Transport: a ZMQ ROUTER on worker rank 0 bound to VLLM_HOST_IP. ZAP admits only the remote workers' addresses; requests carry a random per-engine token and a per-client epoch and sequence, so delayed puts are rejected. None of it is cryptographic. - A copy that fails after its retries (mirror_attempts x mirror_timeout_s) is reported through vllm-project#52838: failed_jobs drops a store and failed_recving recomputes a request whose load failed. Before a failed push is reported, a fence makes the head reject its late attempts; if the fence fails, the mirror stops. - Worker creation gathers errors, addresses, the server endpoint and the client handshake from every rank, so a failure raises on all. A remote worker's compact region is unlinked as soon as it is mapped. - FileMapper tiers (fs, obj, p2p) of multi-node engines store under their own slot_layout namespace unless rows are topology-agnostic. - The cache-reset promotion hold of vllm-project#62929 also covers a remote node's late slot push: a remote worker reports a store only after its push, and fences a failed push's late attempts before reporting it. - The rejections of vllm-project#62930 for external_launcher, an unknown node count (Ray), canonical_layout and replicated_layout stay. Without secondary tiers, regions stay node-local as before. Signed-off-by: Javier López <jlopez@semark.com> Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011NBbUxmYzpDb5p1ScTziyw

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Depends on vllm-project#52838, vllm-project#62930 and vllm-project#62929. With TieringOffloadingSpec, the scheduler and its secondary tiers run in the engine core next to worker rank 0 and read only that node's /dev/shm region, so workers on other nodes write their slots into a region nobody reads (vllm-project#54415). vllm-project#62930 rejects such engines at startup; this lifts the rejection for the multiprocessing executor with nnodes > 1 by mirroring remote slots into the head region. With secondary tiers and workers on several nodes (mp executor, nnodes > 1): - Each worker off the head node keeps a compact region with only its slot. A background thread pushes the slot of each stored chunk to the head region before the store is reported, and pulls it before a load's DMA. Copies move at most 32 MiB per request; loads go first, and a waiting store runs after at most four load requests. - Transport: a ZMQ ROUTER on worker rank 0 bound to VLLM_HOST_IP. ZAP admits only the remote workers' addresses; requests carry a random per-engine token and a per-client epoch and sequence, so delayed puts are rejected. None of it is cryptographic. - A copy that fails after its retries (mirror_attempts x mirror_timeout_s) is reported through vllm-project#52838: failed_jobs drops a store and failed_recving recomputes a request whose load failed. Before a failed push is reported, a fence makes the head reject its late attempts; if the fence fails, the mirror stops. - Worker creation gathers errors, addresses, the server endpoint and the client handshake from every rank, so a failure raises on all. A remote worker's compact region is unlinked as soon as it is mapped. - FileMapper tiers (fs, obj, p2p) of multi-node engines store under their own slot_layout namespace, topology-agnostic rows included: rows stored across nodes before the mirror lack the remote slots. - The cache-reset promotion hold of vllm-project#62929 also covers a remote node's late slot push: a remote worker reports a store only after its push, and fences a failed push's late attempts before reporting it. - The rejections of vllm-project#62930 for external_launcher, an unknown node count (Ray), canonical_layout and replicated_layout stay. Without secondary tiers, regions stay node-local as before. Signed-off-by: Javier López <jlopez@semark.com> Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011NBbUxmYzpDb5p1ScTziyw

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Depends on vllm-project#52838, vllm-project#62930 and vllm-project#62929. With TieringOffloadingSpec, the scheduler and its secondary tiers run in the engine core next to worker rank 0 and read only that node's /dev/shm region, so workers on other nodes write their slots into a region nobody reads (vllm-project#54415). vllm-project#62930 rejects such engines at startup; this lifts the rejection for the multiprocessing executor with nnodes > 1 by mirroring remote slots into the head region. With secondary tiers and workers on several nodes (mp executor, nnodes > 1): - Each worker off the head node keeps a compact region with only its slot. A background thread pushes the slot of each stored chunk to the head region before the store is reported, and pulls it before a load's DMA. Copies move at most 32 MiB per request; loads go first, and a waiting store runs after at most four load requests. - Transport: a ZMQ ROUTER on worker rank 0 bound to VLLM_HOST_IP. ZAP admits only the remote workers' addresses; requests carry a random per-engine token and a per-client epoch and sequence, so delayed puts are rejected. None of it is cryptographic. - A copy that fails after its retries (mirror_attempts x mirror_timeout_s) is reported through vllm-project#52838: failed_jobs drops a store and failed_recving recomputes a request whose load failed. Before a failed push is reported, a fence makes the head reject its late attempts; if the fence fails, the mirror stops. - Worker creation gathers errors, addresses, the server endpoint and the client handshake from every rank, so a failure raises on all. A remote worker's compact region is unlinked as soon as it is mapped. - FileMapper tiers (fs, obj, p2p) of multi-node engines store under their own slot_layout namespace, topology-agnostic rows included: rows stored across nodes before the mirror lack the remote slots. - The cache-reset promotion hold of vllm-project#62929 also covers a remote node's late slot push: a remote worker reports a store only after its push, and fences a failed push's late attempts before reporting it. - The rejections of vllm-project#62930 for external_launcher, an unknown node count (Ray), canonical_layout and replicated_layout stay. Without secondary tiers, regions stay node-local as before. Signed-off-by: Javier López <jlopez@semark.com> Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011NBbUxmYzpDb5p1ScTziyw

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Depends on vllm-project#52838, vllm-project#62930 and vllm-project#62929. With TieringOffloadingSpec, the scheduler and its secondary tiers run in the engine core next to worker rank 0 and read only that node's /dev/shm region, so workers on other nodes write their slots into a region nobody reads (vllm-project#54415). vllm-project#62930 rejects such engines at startup; this lifts the rejection for the multiprocessing executor with nnodes > 1 by mirroring remote slots into the head region. With secondary tiers and workers on several nodes (mp executor, nnodes > 1): - Each worker off the head node keeps a compact region with only its slot. A background thread pushes the slot of each stored chunk to the head region before the store is reported, and pulls it before a load's DMA. Copies move at most 32 MiB per request; loads go first, and a waiting store runs after at most four load requests. - Transport: a ZMQ ROUTER on worker rank 0 bound to VLLM_HOST_IP. ZAP admits only the remote workers' addresses; requests carry a random per-engine token and a per-client epoch and sequence, so delayed puts, also those of a replaced client, are rejected. None of it is cryptographic. - A copy that fails after its retries (mirror_attempts x mirror_timeout_s) is reported through vllm-project#52838: failed_jobs drops a store and failed_recving recomputes a request whose load failed. Before a failed push is reported, a fence makes the head reject its late attempts; if the fence fails, the mirror stops. - Worker creation gathers errors, addresses, the server endpoint and the client handshake from every rank, so a failure raises on all. A remote worker's compact region is unlinked as soon as it is mapped. - FileMapper tiers (fs, obj, p2p) of multi-node engines store under their own slot_layout namespace, topology-agnostic rows included: rows stored across nodes before the mirror lack the remote slots. - The cache-reset promotion hold of vllm-project#62929 also covers a remote node's late slot push: a remote worker reports a store only after its push, and fences a failed push's late attempts before reporting it. - The rejections of vllm-project#62930 for external_launcher, an unknown node count (Ray), canonical_layout and replicated_layout stay. Without secondary tiers, regions stay node-local as before. Signed-off-by: Javier López <jlopez@semark.com> Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011NBbUxmYzpDb5p1ScTziyw

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Depends on vllm-project#52838, vllm-project#62930 and vllm-project#62929. With TieringOffloadingSpec, the scheduler and its secondary tiers run in the engine core next to worker rank 0 and read only that node's /dev/shm region, so workers on other nodes write their slots into a region nobody reads (vllm-project#54415). vllm-project#62930 rejects such engines at startup; this lifts the rejection for the multiprocessing executor with nnodes > 1 by mirroring remote slots into the head region. With secondary tiers and workers on several nodes (mp executor, nnodes > 1): - Each worker off the head node keeps a compact region with only its slot. A background thread pushes the slot of each stored chunk to the head region before the store is reported, and pulls it before a load's DMA. Copies move at most 32 MiB per request; loads go first, and a waiting store runs after at most four load requests. - Transport: a ZMQ ROUTER on worker rank 0 bound to VLLM_HOST_IP. ZAP admits only the remote workers' addresses; requests carry a random per-engine token and a per-client epoch and sequence, so delayed puts, also those of a replaced client, are rejected. None of it is cryptographic. - A copy that fails after its retries (mirror_attempts x mirror_timeout_s) is reported through vllm-project#52838: failed_jobs drops a store and failed_recving recomputes a request whose load failed. Before a failed push is reported, a fence makes the head reject its late attempts; if the fence fails, the mirror stops. - Worker creation gathers errors, addresses, the server endpoint and the client handshake from every rank, so a failure raises on all. A remote worker's compact region is unlinked as soon as it is mapped. - FileMapper tiers (fs, obj, p2p) of multi-node engines store under their own slot_layout namespace, topology-agnostic rows included: rows stored across nodes before the mirror lack the remote slots. - The cache-reset promotion hold of vllm-project#62929 also covers a remote node's late slot push: a remote worker reports a store only after its push, and fences a failed push's late attempts before reporting it. - The rejections of vllm-project#62930 for external_launcher, an unknown node count (Ray), canonical_layout and replicated_layout stay. Without secondary tiers, regions stay node-local as before. Signed-off-by: Javier López <jlopez@semark.com> Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011NBbUxmYzpDb5p1ScTziyw

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Depends on vllm-project#52838, vllm-project#62930 and vllm-project#62929. With TieringOffloadingSpec, the scheduler and its secondary tiers run in the engine core next to worker rank 0 and read only that node's /dev/shm region, so workers on other nodes write their slots into a region nobody reads (vllm-project#54415). vllm-project#62930 rejects such engines at startup; this lifts the rejection for the multiprocessing executor with nnodes > 1 by mirroring remote slots into the head region. With secondary tiers and workers on several nodes (mp executor, nnodes > 1): - Each worker off the head node keeps a compact region with only its slot. A background thread pushes the slot of each stored chunk to the head region before the store is reported, and pulls it before a load's DMA. Copies move at most 32 MiB per request (or one slot, if larger); loads go first, and a waiting store runs after at most four load requests. - Transport: a ZMQ ROUTER on worker rank 0 bound to VLLM_HOST_IP. ZAP admits only the remote workers' addresses; requests carry a random per-engine token and a per-client epoch and sequence, so delayed puts, also those of a replaced client, are rejected. None of it is cryptographic. - A copy that fails after its retries (mirror_attempts x mirror_timeout_s) is reported through vllm-project#52838: failed_jobs drops a store and failed_recving recomputes a request whose load failed. Before a failed push is reported, a fence makes the head reject its late attempts; if the fence fails, the worker raises instead of reporting it, as a late attempt could overwrite a reused chunk. - Worker creation gathers errors, addresses, the server endpoint and the client handshake from every rank, so a failure raises on all. A remote worker's compact region is unlinked as soon as it is mapped. - FileMapper tiers (fs, obj, p2p) of multi-node engines store under their own slot_layout namespace, topology-agnostic rows included: rows stored across nodes before the mirror lack the remote slots. - The cache-reset promotion hold of vllm-project#62929 also covers a remote node's late slot push: a remote worker reports a store only after its push, and fences a failed push's late attempts before reporting it. - The rejections of vllm-project#62930 for external_launcher, an unknown node count (Ray), canonical_layout and replicated_layout stay. The kvcr tier is rejected across nodes: its keys carry no slot_layout namespace. Without secondary tiers, regions stay node-local as before. Signed-off-by: Javier López <jlopez@semark.com> Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011NBbUxmYzpDb5p1ScTziyw

Depends on vllm-project#52838, vllm-project#62930 and vllm-project#62929. With TieringOffloadingSpec, the scheduler and its secondary tiers run in the engine core next to worker rank 0 and read only that node's /dev/shm region, so workers on other nodes write their slots into a region nobody reads (vllm-project#54415). vllm-project#62930 rejects such engines at startup; this lifts the rejection for the multiprocessing executor with nnodes > 1 by mirroring remote slots into the head region. With secondary tiers and workers on several nodes (mp executor, nnodes > 1): - Each worker off the head node keeps a compact region with only its slot. A background thread pushes the slot of each stored chunk to the head region before the store is reported, and pulls it before a load's DMA. Copies move at most 32 MiB per request (or one slot, if larger); loads go first, and a waiting store runs after at most four load requests. - Transport: a ZMQ ROUTER on worker rank 0 bound to VLLM_HOST_IP. ZAP admits only the remote workers' addresses; requests carry a random per-engine token and a per-client epoch and sequence, so delayed puts, also those of a replaced client, are rejected. None of it is cryptographic. - A copy that fails after its retries (mirror_attempts x mirror_timeout_s) is reported through vllm-project#52838: failed_jobs drops a store and failed_recving recomputes a request whose load failed. Before a failed push is reported, a fence makes the head reject its late attempts; if the fence fails, the worker raises instead of reporting it, as a late attempt could overwrite a reused chunk. - Worker creation gathers errors, addresses, the server endpoint and the client handshake from every rank, so a failure raises on all. A remote worker's compact region is unlinked as soon as it is mapped. - FileMapper tiers (fs, obj, p2p) of multi-node engines store under their own slot_layout namespace, topology-agnostic rows included: rows stored across nodes before the mirror lack the remote slots. - The cache-reset promotion hold of vllm-project#62929 also covers a remote node's late slot push: a remote worker reports a store only after its push, and fences a failed push's late attempts before reporting it. - The rejections of vllm-project#62930 for external_launcher, an unknown node count (Ray), canonical_layout and replicated_layout stay. The kvcr tier, under any name that resolves to its class, is rejected across nodes: its keys carry no slot_layout namespace. Without secondary tiers, regions stay node-local as before. Signed-off-by: Javier López <jlopez@semark.com> Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011NBbUxmYzpDb5p1ScTziyw

orozery · 2026-10-25T13:54:39Z

Thanks @javieratomic !
Can we reduce this PR for the minimum required to reject the cases we're addressing?
cc @Etelis PTAL

javieratomic · 2026-10-26T10:57:34Z

Done in 4185ec5: it is down to the minimum, +84/-0 including the test. With secondary tiers and more than one worker, create_worker() checks with in_the_same_node_as() whether the TP, PP and PCP groups each share a node, and raises otherwise. An engine's workers form a grid of those groups, so that covers every multi-node placement (mp with --nnodes, Ray, external_launcher) without looking at the executor. The engine-core placement, Ray single-worker, elastic EP and per-layout checks are all dropped.

Checked on 2× DGX Spark (TP=2, --nnodes 2, facebook/opt-125m): with an fs tier both workers fail at startup with the new error; without secondary tiers it starts and serves, and the same prompt sent twice gives the same output.

TieringOffloadingSpec secondary tiers run in the engine core and read only its node's CPU region. Workers on other nodes write their slots into their own node's region, so the secondary tiers store rows without them and later load stale or uninitialized KV into those ranks (vllm-project#54415). Reject the setup when the workers are created instead: with secondary tiers and more than one worker, each worker checks with in_the_same_node_as() whether its TP, PP and PCP groups share a node. An engine's workers form a grid of those groups, so they all share a node if each group does. Single-node engines and engines without secondary tiers are unchanged. Signed-off-by: Javier López <59578422+javieratomic@users.noreply.github.com> Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01B8SKmHUi4aeTtP6qyf8Xpe

javieratomic · 2026-10-26T13:43:21Z

Pushed daf1a7e with one more fix to the same check. The previous revision raised at the first group that spans nodes, so a rank could skip the PP or PCP collective that other ranks still entered. With an uneven placement, e.g. TP=2 × PP=2 with three workers on one node and one on another, the ranks of the spanning TP group raised at once while the ranks of the node-local TP group blocked in the PP collective, waiting for them, until the executor noticed the dead workers or the gloo timeout expired, instead of failing with the same error right away. Now every rank runs all three collectives and only then raises. The unit test also checks that all three groups are queried when the first one already spans nodes; it fails on the previous revision.

TieringOffloadingSpec's scheduler and secondary tiers run in the engine core, which shares a node with worker rank 0 (the head node), and read only that node's shared CPU region. Workers on other nodes wrote their slots into their own node's region, so secondary tiers stored rows without those slots and promotions never filled them (vllm-project#54415); vllm-project#62930 rejects such engines at startup. This lifts that rejection. Each worker on another node moves its own slot of every chunk between its GPU and the head region with one-sided NIXL transfers (RDMA WRITE and READ over UCX). The head only registers its region; it serves no requests. A store is reported once its slots are in the head region, and a load reads them before the request runs. Loads go ahead of stores on a background copy thread. mirror_source picks what a remote worker transfers from: - cpu: a compact node-local region holding only its slot, filled by the regular offloading DMA and mirrored in transfers of at most 256 MiB; - gpu: its GPU blocks, straight to and from the head region, with the CPU offloading worker's copy plan mapped onto the head slot. It needs GPUDirect RDMA; without it UCX emulates the transfers through host memory, several times slower than cpu; - auto (default): gpu when the driver reports GPUDirect RDMA or dma-buf support for the GPU, cpu otherwise (e.g. GB10). A transfer that ends in an error is reported as a failed transfer. One that reaches no terminal state within mirror_timeout_s may still land on a reused chunk or block, so the worker raises and the engine stops. Placement: secondary tiers on an engine whose TP, PP or PCP groups span nodes get the mirror; the scheduler must join worker rank 0's region. Data parallelism, canonical_layout, replicated_layout and the kvcr tier stay rejected across nodes. FileMapper-keyed tiers use their own namespace on multi-node engines, since rows stored before the mirror lack the remote slots. Signed-off-by: Javier López <59578422+javieratomic@users.noreply.github.com> Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01B8SKmHUi4aeTtP6qyf8Xpe

Signed-off-by: Javier López <59578422+javieratomic@users.noreply.github.com>

TieringOffloadingSpec's scheduler and secondary tiers run in the engine core, which shares a node with worker rank 0 (the head node), and read only that node's shared CPU region. Workers on other nodes wrote their slots into their own node's region, so secondary tiers stored rows without those slots and promotions never filled them (vllm-project#54415); vllm-project#62930 rejects such engines at startup. This lifts that rejection. Each worker on another node moves its own slot of every chunk between its GPU and the head region with one-sided NIXL transfers (RDMA WRITE and READ over UCX). The head only registers its region; it serves no requests. A store is reported once its slots are in the head region, and a load reads them before the request runs. Loads go ahead of stores on a background copy thread. mirror_source picks what a remote worker transfers from: - cpu: a compact node-local region holding only its slot, filled by the regular offloading DMA and mirrored in transfers of at most 256 MiB; - gpu: its GPU blocks, straight to and from the head region, with the CPU offloading worker's copy plan mapped onto the head slot. It needs GPUDirect RDMA; without it UCX emulates the transfers through host memory, several times slower than cpu; - auto (default): gpu when the driver reports GPUDirect RDMA or dma-buf support for the GPU, cpu otherwise (e.g. GB10). A transfer that ends in an error is reported as a failed transfer. One that reaches no terminal state within mirror_timeout_s may still land on a reused chunk or block, so the worker raises and the engine stops. Placement: secondary tiers on an engine whose TP, PP or PCP groups span nodes get the mirror; the scheduler must join worker rank 0's region. Data parallelism, canonical_layout, replicated_layout and the kvcr tier stay rejected across nodes. FileMapper-keyed tiers use their own namespace on multi-node engines, since rows stored before the mirror lack the remote slots. Signed-off-by: Javier López <59578422+javieratomic@users.noreply.github.com> Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01B8SKmHUi4aeTtP6qyf8Xpe

Etelis

The check is in the right place, before allocating the CPU region. One small test change below to make sure we keep that ordering.

Etelis

Other than that it LGTM!

Thanks!

Signed-off-by: Javier López <59578422+javieratomic@users.noreply.github.com> Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Lxs9D9vjV9HGQmKEUGZW8U

Etelis · 2026-10-29T12:37:25Z

/ci run

github-actions · 2026-10-29T12:37:29Z

✅ @javieratomic, CI is now available for this PR.

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github-actions · 2026-10-29T12:40:08Z

✅ Triggered Buildkite CI #98286 for commit 4981fe869b29.

ℹ️ This PR is 1 commit behind upstream main. Merged upstream main into this branch as 4981fe869b29 before starting CI. Pull the branch before pushing more changes.

Signed-off-by: Javier López <59578422+javieratomic@users.noreply.github.com>

TieringOffloadingSpec's scheduler and secondary tiers run in the engine core, which shares a node with worker rank 0 (the head node), and read only that node's shared CPU region. Workers on other nodes wrote their slots into their own node's region, so secondary tiers stored rows without those slots and promotions never filled them (vllm-project#54415); vllm-project#62930 rejects such engines at startup. This lifts that rejection. Each worker on another node moves its own slot of every chunk between its GPU and the head region with one-sided NIXL transfers (RDMA WRITE and READ over UCX). The head only registers its region; it serves no requests. A store is reported once its slots are in the head region, and a load reads them before the request runs. Loads go ahead of stores on a background copy thread. mirror_source picks what a remote worker transfers from: - cpu: a compact node-local region holding only its slot, filled by the regular offloading DMA and mirrored in transfers of at most 256 MiB; - gpu: its GPU blocks, straight to and from the head region, with the CPU offloading worker's copy plan mapped onto the head slot. It needs GPUDirect RDMA; without it UCX emulates the transfers through host memory, several times slower than cpu; - auto (default): gpu when the driver reports GPUDirect RDMA or dma-buf support for the GPU, cpu otherwise (e.g. GB10). A transfer that ends in an error is reported as a failed transfer. One that reaches no terminal state within mirror_timeout_s may still land on a reused chunk or block, so the worker raises and the engine stops. Placement: secondary tiers on an engine whose TP, PP or PCP groups span nodes get the mirror; the scheduler must join worker rank 0's region. Data parallelism, canonical_layout, replicated_layout and the kvcr tier stay rejected across nodes. FileMapper-keyed tiers use their own namespace on multi-node engines, since rows stored before the mirror lack the remote slots. Signed-off-by: Javier López <59578422+javieratomic@users.noreply.github.com> Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

javieratomic requested review from ApostaC, NickLucche, ivanium, orozery, wzhao18 and xuechendi as code owners October 21, 2026 15:37

This was referenced Oct 21, 2026

[KV Offload] Mirror CPU offload region slots across nodes #62933

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[Bug][Feature][KV-offloading]: shared-mmap CPU region assumes all ranks on one host — multi-node engines hang at init; node-local disk tier reference implementation #54415

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mergify Bot added documentation Improvements or additions to documentation kv-connector labels Oct 21, 2026

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javieratomic force-pushed the offload-multinode-validation branch from 3151044 to c3a7d6a Compare October 21, 2026 23:42

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orozery requested a review from Etelis October 26, 2026 13:45

javieratomic added a commit to javieratomic/vllm that referenced this pull request Oct 26, 2026

Merge vllm-project#62930 (base for the mirror; not part of this PR)

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Merge vllm-project#62930 (base for the mirror; not part of this PR)

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Signed-off-by: Javier López <59578422+javieratomic@users.noreply.github.com>

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[KV Offload] Size node-local shared regions by local_world_size #53474

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Merge branch 'main' into offload-multinode-validation

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Merge vllm-project#62930 (base for the mirror; not part of this PR)

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