"malloc failed"

I've been abusing Git for a purpose it wasn't intended to serve: archiving a large number of files with many duplicates and near-duplicates. Every once in a while, when trying to do something really big, it tells me "malloc failed" and bails out (I think it's during "git add" but because of the way I issued the commands I can't tell: it could have been a commit or a gc). This is on a 64-bit linux machine with 8G of ram and plenty of swap space, so I'm surprised.

Git is doing an amazing job at archiving and compressing all this stuff I'm putting in it, but I have to do it a wee bit at a time or it craps out. Bug?