I'm very skeptical that this actually makes things faster. For one, zstd is definitely going to be CPU bound rather than I/O bound. But even if it wasn't, there

I'm very skeptical that this actually makes things faster. For one, zstd is definitely going to be CPU bound rather than I/O bound. But even if it wasn't, there shouldn't be a performance benefit to reading a file sequentially using mmap compared to reading it sequentially using read, which you can easily verify yourself by writing a small program that just reads files both ways.