Re: [PATCH v2 01/13] mm: support madvise(MADV_FREE)

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.