What should be innodb_buffer_pool_chunk_size for pool_size=2G, pool_instances=2? I have 4G VPS with following config

innodb_buffer_pool_size=2048M
innodb_buffer_pool_instances=2

SELECT @@innodb_buffer_pool_chunk_size/1024/1024
128.00000000


Should I change innodb_buffer_pool_chunk_size or let it be default?
You should leave the innodb_buffer_pool_chunk_size "as is".

Last year, Percona published some nice formulas to figure out the best chunk size

determine_best_chunk_size{
  if innodb_buffer_pool_size / innodb_buffer_pool_instances &lt; innodb_buffer_pool_chunk_size
  then
    innodb_buffer_pool_chunk_size = roundDownMB(innodb_buffer_pool_size / innodb_buffer_pool_instances)
  fi
}
determine_amount_of_chunks{
  innodb_buffer_amount_chunks_per_instance = roundDown(innodb_buffer_pool_size / innodb_buffer_pool_instances / innodb_buffer_pool_chunk_size)

  if innodb_buffer_amount_chunks_per_instance * innodb_buffer_pool_instances * innodb_buffer_pool_chunk_size - innodb_buffer_pool_size &gt; 1024*1024
  then
    innodb_buffer_amount_chunks_per_instance++
  fi
}

determine_best_chunk_size
determine_amount_of_chunks

innodb_buffer_pool_size = innodb_buffer_pool_instances * innodb_buffer_pool_chunk_size * innodb_buffer_amount_chunks_per_instance


Since you have only 2GB for the Buffer Pool, it is definitely not worth the effort to do any tuning,