NNX: fix sharding#4215
Closed
hsuan-lun-chiang wants to merge 3 commits into
Closed
Conversation
In pure NNX training runs, model variables retrieve physical PartitionSpecs via `get_nnx_named_sharding_with_scan_axis` in `maxtext_utils.py`. Previously, this helper used Flax core SPMD's `from_sharding_rules` to map logical names to physical axes. However, `from_sharding_rules` resolves rules by converting the rules list into a dictionary (last-write-wins). This caused fallback rules sharing the same logical name (e.g. 'embed') to overwrite preceding specific rules, dropping essential axes like `fsdp_transpose` and leading to unsharded parameter percentage assertion errors. Additionally, resolving specifications independently for each dimension without tracking assigned axes could bind a single physical axis (like `fsdp_transpose`) to multiple positional dimensions of a tensor, causing `DuplicateSpecError`. To fix this: 1. Replaced `from_sharding_rules` with a Rules-first resolution loop that matches rules sequentially (first-match-wins), matching Flax Linen's mapping behavior. 2. Implemented an `assigned_axes` tracker within the loop to ensure physical mesh axes are bound to at most one dimension per tensor. 3. Added unit tests covering sequential matching (first-match-wins) and duplicate physical axis prevention during resolution.
PR6-PR10 promoted every routed-to-Linen feature to NNX-native; PR#2885 lands NNX-native pipeline parallelism. This PR flips the three defaults in base.yml so NNX is the production path, and bundles the NNX-only fixes that surface once pure_nnx=True (DiLoCo merge/checkpoint, Zero-1 input shardings on flat nnx.State, MTP sown-Variable handling, generate_param_only_checkpoint NNX flow, maxengine Linen-parity removal).
hsuan-lun-chiang
changed the title
Codecov Report❌ Patch coverage is 📢 Thoughts on this report? Let us know! |
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
PR6-PR10 promoted every routed-to-Linen feature to NNX-native; PR#2885 lands NNX-native pipeline parallelism. This PR flips the three defaults in base.yml so NNX is the production path, and bundles the NNX-only fixes that surface once pure_nnx=True (DiLoCo merge/checkpoint, Zero-1 input shardings on flat nnx.State, MTP sown-Variable handling, generate_param_only_checkpoint NNX flow, maxengine Linen-parity removal).
Description
Start with a short description of what the PR does and how this is a change from
the past.
The rest of the description includes relevant details and context, examples:
If the change fixes a bug or a Github issue, please include a link, e.g.,:
FIXES: b/123456
FIXES: #123456
You can also provide a comma-separated list. If you don't want to close a bug but
simply to reference it, use BUGS, e.g.:
BUGS: b/123456
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
Before submitting this PR, please make sure (put X in square brackets):
gemini-reviewlabel.