lmdb Cannot allocate memory

[Yu-Chunmiao]

When I rerun this code, this error occured.
env = lmdb.open(params.db_path, map_size=map_size, max_dbs=6)
lmdb.MemoryError: utils/../data/WN18RR_v1/subgraphs_en_True_neg_1_hop_3: Cannot allocate memory