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fix(nnx): fix gpt3 paxml checkpoint conversion state map and layout #4555

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fix(nnx): fix gpt3 paxml checkpoint conversion state map and layout #4555

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15 changes: 15 additions & 0 deletions src/maxtext/checkpoint_conversion/standalone_scripts/convert_gpt3_ckpt_from_paxml.py
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Original file line number Diff line number Diff line change
Expand Up @@ -213,6 +213,7 @@ def init_state_fn():
state_map = {
"['optimizer']['step'].value": ("step", None),
"['optimizer']['opt_state'][0]['count'].value": ("opt_states_0.no_prefix_0.count", None),
"['optimizer']['opt_state']['count'].value": ("opt_states_0.no_prefix_0.count", None),
}

@xibinliu xibinliu Jul 24, 2026

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Instead of handle the NNX state mapping, can we convert NNX state to Linen layout here, so all the linen mapping can be used directly?

if cfg.pure_nnx:
      state = train_state_nnx.to_checkpoint_dict(state)

else:
state_map = {
Expand All @@ -237,10 +238,18 @@ def get_layer_prefix(keystr_pax):
f"opt_states_0.{prefix_pax_opt_state}.m{keystr_pax}",
transform_fn,
)
state_map[f"['optimizer']['opt_state']['mu']{keystr_maxtext}.value"] = (
f"opt_states_0.{prefix_pax_opt_state}.m{keystr_pax}",
transform_fn,
)
state_map[f"['optimizer']['opt_state'][0]['nu']{keystr_maxtext}.value"] = (
f"opt_states_0.{prefix_pax_opt_state}.v{keystr_pax}",
transform_fn,
)
state_map[f"['optimizer']['opt_state']['nu']{keystr_maxtext}.value"] = (
f"opt_states_0.{prefix_pax_opt_state}.v{keystr_pax}",
transform_fn,
)
else:
state_map[f".params['params']{keystr_maxtext}"] = (f"mdl_vars{keystr_pax}", transform_fn)
state_map[f".opt_state.mu['params']{keystr_maxtext}"] = (
Expand All @@ -254,6 +263,8 @@ def get_layer_prefix(keystr_pax):

def verify_fn(key_path, _):
keystr = jax.tree_util.keystr(key_path)
if "['rngs']" in keystr:
return

@xibinliu xibinliu Jul 24, 2026

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'rngs' should have been filtered out, if we convert to linen format first. See above comments.

assert keystr in state_map, f"{keystr} not found"

jax.tree_util.tree_map_with_path(verify_fn, state)
Expand All @@ -264,6 +275,8 @@ def verify_fn(key_path, _):

def map_fn(key_path, value):
key_path_str = jax.tree_util.keystr(key_path)
if "['rngs']" in key_path_str:
return value

@xibinliu xibinliu Jul 24, 2026

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ditto

file_path, transform_fn = state_map[key_path_str]
full_path = os.path.join(paxml_ckpt_prefix, file_path)
spec = {"driver": "zarr", "metadata_key": ".zarray", "kvstore": {}}
Expand Down Expand Up @@ -303,6 +316,8 @@ def map_fn(key_path, value):
max_utils.print_mem_stats("converted state finished")

step_value = int(converted_state.optimizer.step.value) if cfg.pure_nnx else converted_state.step
if cfg.pure_nnx:
converted_state = train_state_nnx.to_checkpoint_dict(converted_state)
if checkpointing.save_checkpoint(checkpoint_manager, step_value, converted_state):

@xibinliu xibinliu Jul 24, 2026

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There is the similar conversion in maybe_save_checkpoint in src/maxtext/common/checkpointing.py:

  if config.pure_nnx:
    # Save in the Linen on-disk layout so pure_nnx and Linen checkpoints are interchangeable.
    if config.enable_diloco:
      # DiLoCoTrainState: persist the synchronized global model (outer params).
      # The per-replica inner optimizer / outer-momentum state is not checkpointed.
      step_value = state.step.get_value() if hasattr(state.step, "get_value") else state.step
      state = train_state_nnx.to_linen_checkpoint_dict({"model": state.params, "optimizer": {"step": step_value}})
    else:
      # rngs/dropout/batch-stats are packed under items/nnx_aux so the RNG/dropout
      # stream continues across resumes instead of resetting to a base key.
      state = train_state_nnx.to_checkpoint_dict(state)

Let's move this conversion from maybe_save_checkpoint to save_checkpoint so we don't have to do the conversion in all the callers.

max_logging.log(f"saved a checkpoint at step {step_value}")
# Upon preemption, exit when and only when all ongoing saves are complete.
Expand Down
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