fix user-specified max_session_len

[grimoire]

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[zhulinJulia24]

LGTM. test case passed！

[lvhan028]

What if num_gpu_blocks=1?

[grimoire]

lmdeploy/lmdeploy/pytorch/engine/executor/base.py

Line 131 in 22a188a

if int(num_available) // cache_block_size >= 16:

block size would not less than 16

[lvhan028]

from lmdeploy import PytorchEngineConfig, pipeline

engine_config = PytorchEngineConfig(num_gpu_blocks=1)

model_path = 'Qwen/Qwen3-0.6B'
pipe = pipeline(model_path, backend_config=engine_config)

prompt = 'hi'

response = pipe(prompt)

print(response)

The response is:

2025-08-04 10:43:56,473 - lmdeploy - ERROR - async_engine.py:844 - session 0 finished, reason "error"
Response(text='internal error happened', generate_token_len=0, input_token_len=14, finish_reason='error', token_ids=[], logprobs=None, logits=None, last_hidden_state=None, index=0

[lvhan028]

This appears to be more of a workaround than a root cause fix. We might need a more permanent solution to address the root cause later.