> I posted a patch doing exactly iovec madvise. Doesn't support MADV_FREE yet
> though, but should be easy to do it.
> 
> http://marc.info/?l=linux-mm&m=144615663522661&w=2

I think that would be a great way to deal with this. It keeps the nice
property of still being able to drop pages in allocations that have been
handed out but not yet touched. The allocator just needs to be designed
to do lots of purging in one go (i.e. something like an 8:1 active:clean
ratio triggers purging and it goes all the way to 16:1).