The holocaust was a genocide, but there are still jews left in the world. Not for the lack of trying, but Hitler was stopped, so you can definitely do a partial genocide.
Genocide is the attempted destruction of a group of people. If you only kill one person, but it was part of some supervillain plot to kill everyone, it's still genocide, you just failed at it.
Nah, you can aim to genocide a group of people but it's just not viable so you genocide them just a little, like the forced sterilisation of minorities that's happening in multiple places. That certainly qualifies as some little genocide.