[Diloco] Diloco trainer

[khatwanimohit]

Description

This PR introduces support for Distributed Low-Communication (DiLoCo) training in MaxText. It implements both standard DiLoCo, enabling efficient model training across disjoint clusters ("islands") by synchronizing gradients infrequently via an outer optimizer.

Key Changes

• Core Logic: Added src/MaxText/diloco.py, which implements the DiLoCoTrainState, inner/outer optimization steps,
  and communication synchronization using drjax.
• Training Loop Integration: Modified src/MaxText/train.py to initialize the DiLoCo state and adapt the training
  step when enable_diloco is active. This includes handling data reshaping for multiple replicas.
• Sharding & Configuration:
  • Updated src/MaxText/sharding.py to support a hierarchical "diloco" sharding axis.
  • Added new flags (e.g., enable_diloco, num_diloco_replicas, diloco_outer_optimizer) to base.yml and types.py.
• Dependencies: Added drjax to the project requirements.
• Testing: Added comprehensive unit tests in tests/diloco_test.py.

Notice 1: Once all tests pass, the "pull ready" label will automatically be assigned.
This label is used for administrative purposes. Please do not add it manually.

Notice 2: For external contributions, our settings currently require an approval from a MaxText maintainer to trigger CI tests.

Tests

Please describe how you tested this change, and include any instructions and/or
commands to reproduce.

Checklist

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• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.

[codecov]

Codecov Report

❌ Patch coverage is 77.03704% with 31 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/MaxText/diloco.py	83.33%	13 Missing and 2 partials ⚠️
src/MaxText/train_utils.py	22.22%	11 Missing and 3 partials ⚠️
src/MaxText/data_loader.py	60.00%	1 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

[khatwanimohit]

Add train_compile tests for Diloco