Amalekites, don't they ever quit? Apparently not in chapter 30. Now I'll say that I'm fine with standing on what I had said before, but here there may be yet another possibility as to what's going on. It might be that the story in chapter 27 is a telescoping of several events into a single story, and the time that David wiped out the Amalekites in that chapter was actually an out-of-order version of this story, if you follow. This time, despite the claim of the marginal note on verse 17, the genocide is not complete, nor was it unprovoked.
The SAB says "David just keeps getting more wives." While true in a more general sense, there are no new wives in this chapter, David still being at two or three, depending on whether you count Michal. There is also a note once again concerning Abiathar's dubious lineage.
After the battle, David decides that those people who stayed behind to guard the supplies deserve the spoils of war just as much as those who rode out for the battle.
This battle was indeed violent, but I have nothing to add to comments I've given before in this book and in other places.