Regarding `private[this]`, we don't really use it elsewhere, so I'd skip it here. It would be a bigger change to convert the whole codebase to `private[this]`. Its main benefit seems to be in terms of code generated but that kind of stuff usually gets inlined anyway.

I now see that this is per-task, not a blacklist for the whole executor, so it makes sense for the variable name to contain "task". In that case maybe call this `spark.scheduler.executorTaskBlacklistTime` -- I think it's good to put "scheduler" as the first component there since it's not really a property of tasks.