[Core] Add `reload_weights` RPC method #20096

22quinn · 2025-06-25T21:22:30Z

Essential Elements of an Effective PR Description Checklist

The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
The test plan, such as providing test command.
The test results, such as pasting the results comparison before and after, or e2e results
(Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

Purpose

See #19886

Test Plan

See #19640

Test Result

See #19640

(Optional) Documentation Update

Signed-off-by: 22quinn <[email protected]>

gemini-code-assist

Summary of Changes

Hello @22quinn, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces the core functionality for a new reload_weights RPC method, enabling the dynamic, in-place reloading of model weights for both GPU and TPU workers. This change refactors existing model loading logic to clearly separate initial model loading from subsequent weight reloading, and it includes improvements to memory pool context management.

Highlights

Support for reload_weights RPC: Core reload_weights methods have been added to GPUModelRunner and TPUModelRunner to facilitate in-place reloading of model weights, laying the groundwork for an RPC method.
Worker-level exposure: The new reload_weights functionality is exposed at the GPUWorker and TPUWorker levels, allowing higher-level components to trigger weight reloads.
Refactored model loading: The load_model methods in GPUModelRunner and TPUModelRunner have been simplified to always perform a full model load, removing the previous conditional in-place weight reloading logic.
Memory pool context helper: A new private helper method _maybe_get_memory_pool_context was introduced in GPUWorker to centralize and simplify the management of memory pool contexts during model and KV cache operations.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point in your pull request via creating an issue comment (i.e. comment on the pull request page) using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands.

Feature	Command	Description
Code Review	`/gemini review`	Performs a code review for the current pull request in its current state.
Pull Request Summary	`/gemini summary`	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in issue comments and review comments.
Help	`/gemini help`	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist is currently in preview and may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments to provide feedback.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

github-actions · 2025-06-25T21:23:43Z

👋 Hi! Thank you for contributing to the vLLM project.

💬 Join our developer Slack at https://slack.vllm.ai to discuss your PR in #pr-reviews, coordinate on features in #feat- channels, or join special interest groups in #sig- channels.

Just a reminder: PRs would not trigger full CI run by default. Instead, it would only run fastcheck CI which starts running only a small and essential subset of CI tests to quickly catch errors. You can run other CI tests on top of those by going to your fastcheck build on Buildkite UI (linked in the PR checks section) and unblock them. If you do not have permission to unblock, ping simon-mo or khluu to add you in our Buildkite org.

Once the PR is approved and ready to go, your PR reviewer(s) can run CI to test the changes comprehensively before merging.

To run CI, PR reviewers can either: Add ready label to the PR or enable auto-merge.

🚀

gemini-code-assist

Code Review

This pull request introduces a reload_weights RPC method, which is a valuable addition for dynamically updating model weights. The implementation is clean and consistent across both GPU and TPU workers. The refactoring of load_model to separate concerns is a good design choice, and the consolidation of memory pool context logic in the GPU worker improves code quality.

My main feedback is on a potential side effect of the load_model refactoring in gpu_model_runner.py, which now always reloads the model from scratch. This changes its previous behavior and might affect existing callers or tests that expect an in-place weight reload. Please see the detailed comment on this.

vllm/v1/worker/gpu_model_runner.py

Signed-off-by: 22quinn <[email protected]>

mergify · 2025-06-28T05:54:20Z

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @22quinn.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

Signed-off-by: 22quinn <[email protected]>

houseroad

One comment, otherwise, looks good to me.

houseroad · 2025-07-18T04:05:34Z

vllm/v1/worker/tpu_model_runner.py

@@ -1192,6 +1186,11 @@ def load_model(self) -> None:
            self.model = model
        self.sampler = TPUSampler()

+    def reload_weights(self) -> None:
+        model_loader = get_model_loader(self.load_config)


nit: can we have a sanity check that model is loaded already?

@houseroad good call. Added an assertion and a corresponding unit test

mergify · 2025-07-18T18:29:48Z

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @22quinn.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

Signed-off-by: 22quinn <[email protected]>

mergify · 2025-07-19T01:03:55Z

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @22quinn.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

Signed-off-by: 22quinn <[email protected]>

hydrozhao · 2025-07-27T08:24:33Z

vllm/v1/worker/gpu_worker.py

            self.model_runner.load_model(eep_scale_up=eep_scale_up)

    def update_config(self, overrides: dict[str, Any]) -> None:
        self.model_runner.update_config(overrides)

+    def reload_weights(self) -> None:
+        with self._maybe_get_memory_pool_context(tag="weights"):


Should delete this line? Because the precondition of reload_weights is that params are already created and memory pool is not reentrant.

If using the default loader below, new params are not created, but it's dependent on individual model's load_weights implementation? cc @youkaichao @ywang96 do you feel appropriate to remove?

vllm/vllm/model_executor/model_loader/weight_utils.py

Lines 614 to 628 in 15a72ac

def default_weight_loader(param: torch.Tensor,

loaded_weight: torch.Tensor) -> None:

"""Default weight loader."""

try:

if param.numel() == 1 and loaded_weight.numel() == 1:

# Sometimes scalar values aren't considered tensors with shapes

# so if both param and loaded_weight are a scalar,

# "broadcast" instead of copy

param.data.fill_(loaded_weight.item())

else:

assert param.size() == loaded_weight.size(), (

f"Attempted to load weight ({loaded_weight.size()}) "

f"into parameter ({param.size()})")

param.data.copy_(loaded_weight)

Signed-off-by: 22quinn <[email protected]> Signed-off-by: avigny <[email protected]>

Signed-off-by: 22quinn <[email protected]> Signed-off-by: shuw <[email protected]>

Signed-off-by: 22quinn <[email protected]> Signed-off-by: x22x22 <[email protected]>

Signed-off-by: 22quinn <[email protected]>

Separate model and weights loading RPC

2a9bbc1

Signed-off-by: 22quinn <[email protected]>

gemini-code-assist bot reviewed Jun 25, 2025

View reviewed changes

mergify bot added v1 tpu Related to Google TPUs labels Jun 25, 2025

gemini-code-assist bot reviewed Jun 25, 2025

View reviewed changes

vllm/v1/worker/gpu_model_runner.py Show resolved Hide resolved

unit test

0e88ddf

Signed-off-by: 22quinn <[email protected]>

22quinn requested review from yeqcharlotte, jeejeelee, simon-mo, youkaichao and houseroad June 25, 2025 21:41

22quinn marked this pull request as ready for review June 25, 2025 21:41

22quinn requested review from WoosukKwon, robertgshaw2-redhat, njhill, ywang96, comaniac and alexm-redhat as code owners June 25, 2025 21:41

fix ci

a8a36fe

Signed-off-by: 22quinn <[email protected]>

mergify bot added the needs-rebase label Jun 28, 2025

rebase

4b01795

Signed-off-by: 22quinn <[email protected]>

mergify bot removed the needs-rebase label Jun 29, 2025

rebase

e489d38

Signed-off-by: 22quinn <[email protected]>

22quinn added the ready ONLY add when PR is ready to merge/full CI is needed label Jul 17, 2025

houseroad reviewed Jul 18, 2025

View reviewed changes

mergify bot added the needs-rebase label Jul 18, 2025

rebase

df5f94d

Signed-off-by: 22quinn <[email protected]>

assert model is loaded before reloading weights + unit test

5ee0a1d

Signed-off-by: 22quinn <[email protected]>

mergify bot removed the needs-rebase label Jul 18, 2025

houseroad approved these changes Jul 18, 2025

View reviewed changes

houseroad enabled auto-merge (squash) July 18, 2025 23:48

mergify bot added the needs-rebase label Jul 19, 2025

resolve merge conflicts

82fa546

Signed-off-by: 22quinn <[email protected]>

auto-merge was automatically disabled July 19, 2025 05:36
Head branch was pushed to by a user without write access

mergify bot removed the needs-rebase label Jul 19, 2025

simon-mo merged commit 5c9b807 into vllm-project:main Jul 23, 2025
62 of 65 checks passed

LyrisZhong pushed a commit to LyrisZhong/vllm that referenced this pull request Jul 23, 2025

[Core] Add reload_weights RPC method (vllm-project#20096)

bfe963c

Signed-off-by: 22quinn <[email protected]>

wangxiyuan mentioned this pull request Jul 24, 2025

[Feature]: support update_config interface vllm-project/vllm-ascend#1976

Open

hydrozhao reviewed Jul 27, 2025

View reviewed changes

avigny pushed a commit to avigny/vllm that referenced this pull request Jul 31, 2025

[Core] Add reload_weights RPC method (vllm-project#20096)

82c6637

Signed-off-by: 22quinn <[email protected]> Signed-off-by: avigny <[email protected]>

wenscarl pushed a commit to wenscarl/vllm that referenced this pull request Aug 4, 2025

[Core] Add reload_weights RPC method (vllm-project#20096)

300026d

Signed-off-by: 22quinn <[email protected]> Signed-off-by: shuw <[email protected]>

x22x22 pushed a commit to x22x22/vllm that referenced this pull request Aug 5, 2025

[Core] Add reload_weights RPC method (vllm-project#20096)

7ad7a24

Signed-off-by: 22quinn <[email protected]> Signed-off-by: x22x22 <[email protected]>

Pradyun92 pushed a commit to Pradyun92/vllm that referenced this pull request Aug 6, 2025

[Core] Add reload_weights RPC method (vllm-project#20096)

c17e6e0

Signed-off-by: 22quinn <[email protected]>

npanpaliya pushed a commit to odh-on-pz/vllm-upstream that referenced this pull request Aug 6, 2025

[Core] Add reload_weights RPC method (vllm-project#20096)

6562d83

Signed-off-by: 22quinn <[email protected]>

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Uh oh!

[Core] Add `reload_weights` RPC method #20096

[Core] Add `reload_weights` RPC method #20096

22quinn commented Jun 25, 2025 •

edited by github-actions bot

Loading

Uh oh!

gemini-code-assist bot left a comment

Uh oh!

github-actions bot commented Jun 25, 2025

Uh oh!

gemini-code-assist bot left a comment

Uh oh!

Uh oh!

mergify bot commented Jun 28, 2025

Uh oh!

houseroad left a comment

Uh oh!

houseroad Jul 18, 2025

Uh oh!

22quinn Jul 18, 2025

Uh oh!

mergify bot commented Jul 18, 2025

Uh oh!

mergify bot commented Jul 19, 2025

Uh oh!

Uh oh!

hydrozhao Jul 27, 2025 •

edited

Loading

Uh oh!

22quinn Jul 28, 2025

Uh oh!

Uh oh!

	def default_weight_loader(param: torch.Tensor,
	loaded_weight: torch.Tensor) -> None:
	"""Default weight loader."""
	try:
	if param.numel() == 1 and loaded_weight.numel() == 1:
	# Sometimes scalar values aren't considered tensors with shapes
	# so if both param and loaded_weight are a scalar,
	# "broadcast" instead of copy
	param.data.fill_(loaded_weight.item())
	else:
	assert param.size() == loaded_weight.size(), (
	f"Attempted to load weight ({loaded_weight.size()}) "
	f"into parameter ({param.size()})")

	param.data.copy_(loaded_weight)

Uh oh!

[Core] Add reload_weights RPC method #20096

[Core] Add reload_weights RPC method #20096

Conversation

22quinn commented Jun 25, 2025 • edited by github-actions bot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Essential Elements of an Effective PR Description Checklist

Purpose

Test Plan

Test Result

(Optional) Documentation Update

Uh oh!

gemini-code-assist bot left a comment

Choose a reason for hiding this comment

Summary of Changes

Highlights

Footnotes

Uh oh!

github-actions bot commented Jun 25, 2025

Uh oh!

gemini-code-assist bot left a comment

Choose a reason for hiding this comment

Code Review

Uh oh!

Uh oh!

mergify bot commented Jun 28, 2025

Uh oh!

houseroad left a comment

Choose a reason for hiding this comment

Uh oh!

houseroad Jul 18, 2025

Choose a reason for hiding this comment

Uh oh!

22quinn Jul 18, 2025

Choose a reason for hiding this comment

Uh oh!

mergify bot commented Jul 18, 2025

Uh oh!

mergify bot commented Jul 19, 2025

Uh oh!

Uh oh!

hydrozhao Jul 27, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

22quinn Jul 28, 2025

Choose a reason for hiding this comment

Uh oh!

Uh oh!

[Core] Add `reload_weights` RPC method #20096

[Core] Add `reload_weights` RPC method #20096

22quinn commented Jun 25, 2025 •

edited by github-actions bot

Loading

hydrozhao Jul 27, 2025 •

edited

Loading