[ethereum/go-ethereum] Memory used increasing slowly (#17450)

#### System information

Geth version: `1.8.12 stable`
OS & Version: Linux 16.04

#### Expected behaviour

Memory usage stays constant

#### Actual behaviour

Hi @karalabe,

im running the node without the rpcapis, the node started 3 days ago using 1.9% of my RAM (8gb). Now is consuming 2.3% and it keeps increasing slowly (like 10mb / h).

I ran the node without specifing the —cache flag, so i assume it is using 1gb.

Is this something that i must worry about or maybe is related with the garbage collection?

#### Steps to reproduce the behaviour

I ran the node with this command:

geth —datadir e1/ —syncmode ‘full’ —port 30357 —rpc —rpcport 8545 —rpccorsdomain ‘*’ —rpcaddr ‘server_ip’ —ws —wsaddr «server_ip» —wsorigins «some_ip» —wsport 9583 —wsapi ‘db,eth,net,web3,txpool,miner’ —networkid 21 —gasprice ‘1’