Not sure where the right place to record this is, but I asked a friend who had encountered issues diagnosing pinned-memory induced fragmentation what tools might have helped with the job, and this was the reply: “default output of any of the memory inspecting tools to know what fraction of the heap is pinned memory (it took a little while to realize that’s what was going on), and some kind of way to work backwards through heap references to the thing that’s retaining pinned memory (or anything, even when it’s not pinned memory)”
I think it makes sense to encourage people to only use pinned memory when appropriate, but since we know pinned memory will need to be used some places, and will cause fragmentation when used, improving the tooling on profiling in the ways suggested (or other ways, more creative) should be on the radar.