Expediting membarrier()

Thanks, that is expressed better than I managed. I can see why this could be hard (who knows what all those other processors might be up to right now, or soon?) but a pessimistic approach would fail by interrupting all, which is what they are planning anyway.

It takes so long to change mappings... maybe a list of processors that already have the page of interest mapped, that are favored to run processes that have used it lately? Maybe this sounds too much like Touching The Scheduler.