Memory usage increases after upgrading to 5.0.23

I have upgraded my mongodb from 4.4 to 5.0.23 and resharded a collection with 10 billion docs about 350GB. It lasted about 5 hours to complish.Then, I found the memory usage increased for each shard,such as from 48% change to 62%, from 56% change to 74%.Is that normal? If not, what shoud I do? Thanks.