extreme memory usage with crossbeam-epoch

[xacrimon]

So I have been developing something very similar to crossbeam-epoch for a little while now and I wanted to write some tests for defer speeds. I did however run into a pretty severe issue with crossbeam using extreme amounts of memory very quickly and getting OOM killed.

Reproducible example at https://github.com/xacrimon/flize/blob/master/bench/src/main.rs.

[taiki-e]

I'm not familiar with epoch, so it may not the correct solution, but this seems can workaround by calling guard.flush() regularly. (commit, result, output of cargo run --release, heap profile for original example)

[taiki-e]

cc @stjepang

[taiki-e]

Ah, this seems a similar issue as #540.