Oh! Hmm... In Swedish, this ending for a surname makes no sense, it means nothing. Yet it is quite common. Practically all other common endings in Swedish surnames mean something.

-son (most common, "son of")
-dal (valley)
-berg (mountain)
-ström (river)
-bäck (stream)
... etc

The -in ending is also common, but I think the meaning has been lost in time, or maybe the names are originally foreign. This type of names are quite common though so it seems a bit unlikely. Some common names like this are Bolin, Dalin, Salin, Modin, Molin, Nordin, Vallin, Melin, Kalin. The emphasis is always on the end syllable.

It's been interesting, as I've been studying Russian, to find that Russian surnames also are based on descriptions of the place where a family might have lived. Most Finnish surnames are also formed this way. In English, it is more common with surnames based on ancient professions but that is less common in Swedish. Not sure about Russian.