Recycler in 'Memory Management for Big Data'#40

At the end of your excellent blog on 'Memory Management for Big Data' (https://github.com/frankmcsherry/blog/blob/master/posts/2017-07-27.md) you mentioned using your recycler project. I shared your blog with some colleagues, and their feedback on this point was: "I also followed the link to have a look at ‘recycler’. It seems like a small Rust shortcoming that it’s worth having a library whose main purpose is to provide typed memory caching. I would think (hope?) that the Rust allocator would be clever enough (in terms of releasing/acquiring memory to/from the OS) to make this a fairly limited optimisation. I notice the ‘recycler’ code is fairly old and wonder if this is still a worthwhile procedure?" and: "Yeah 'recycler' looks like another memory allocator ... I wonder why that would be useful." If you have a moment to elaborate on how the recycler helps here, would be very grateful. Thanks!