The original use case (I believe) was tcmalloc. Tcmalloc maintained per-thread caches of free memory, but that's wasteful since it increases fragmentation but h

The original use case (I believe) was tcmalloc. Tcmalloc maintained per-thread caches of free memory, but that's wasteful since it increases fragmentation but has no parallelism advantage compared to per-CPU buffers. OTOH, you can't just use per-CPU data since you can get preempted, hence rseq. malloc from the per-CPU cache without locking, and free to any other cache without locking.