> In the common case it will be passed many pages by the allocator. There
> will still be a layer of purging logic on top of MADV_FREE but it can be
> much thinner than the current workarounds for MADV_DONTNEED. So the
> allocator would still be coalescing dirty ranges and only purging when
> the ratio of dirty:clean pages rises above some threshold. It would be
> able to weight the largest ranges for purging first rather than logic
> based on stuff like aging as is used for MADV_DONTNEED.

I would expect that jemalloc would just start putting the dirty ranges
into the usual pair of red-black trees (with coalescing) and then doing
purging starting from the largest spans to get back down below whatever
dirty:clean ratio it's trying to keep. Right now, it has all lots of
other logic to deal with this since each MADV_DONTNEED call results in
lots of zeroing and then page faults.