Like if the trend continues it would be about equal with mmap at 64kb buffer size. No way to know for sure without testing it, but that really jumped out at me.
With mmap() of course we only ever have one syscall to create the initial mapping. Everything else is a memory read.
We can get read() down to just one syscall too, with a 4G buffer ;) I can't recall if GB sized buffers are possible, but I have certainly used MB sized read buffers for exactly this reason.
On Linux, read() (and similar system calls) will transfer at most 0x7ffff000
(2,147,479,552) bytes, returning the number of bytes actually transferred.
(This is true on both 32-bit and 64-bit systems.)Here's the catch: Large buffer sizes only increase efficiency for sequential reads. mmap() is still much faster for random access within a file. Doubly so, because we need to not just read() but also lseek() for every read.
The inefficiencies of read() can be minimized in the sequential case only.