After doing a mysqldump server is unresponsive (swapping)

I do a mysqldump manually every night.

I just noticed that after it is done and I try to access the website it is very slow. After I take a look at the free -mh I notice that the server is now swapping when it otherwise wasn't before the mysqldump.

What am I to do in this case? Just restart the server every time I backup? That doesn't seem very effective.

My database file raw is 1.1gb after the dump.