Ostmarken?

Hello! This is my first post here and I'm hoping someone with more familiarity with Norway place names can help me. My 4x great grandfather Martin Larson was born in Norway but moved to Sweden as a young man. I've been fortunate enough to find Martin on several Swedish church records and many of them specifically say he was from "Ostmarken, Norge." I've had a little trouble identifying exactly where this is: there is the forested area around Oslo called Ostmarka, but I can't tell if that's what the area would have been called in the 1870s when the records I'm looking at were written. Then there's an area in Trondheim in the Lade district that seems to be called Ostmarken, but that seems so specific (wouldn't he have just told the person filling out the Swedish church records he was from Trondheim?). Does anyone have any ideas? Also, one record seems to have a more specific place name along side Ostmarken, but I can't make it out. It could maybe be Holwaland or Kolwaland? I realize that probably doesn't help much but thought I should mention it anyway. Thanks for any help at all on this!