A complete read-only filesystem? So no possibility of any form of disk based caching on the whole environment? Not sure if it truly works, but, logically this approach should work:
# Disable datasets caching
from datasets import set_caching_enabled
set_caching_enabled(False)
# Load from disk and keep fully in memory
load_from_disk(path, keep_in_memory=True)
If you have to do extensive preparations / mapping and run into mem issues (beside doing the splitting), process/map the dataset to final usability and remove any not required columns BEFORE saving to disk and uploading to the readonly filesystem.
If that doesnt work: Split and then save and upload.