I'm puzzled by the idea of a system being leaner/faster with n copies of a library in physical RAM rather than 1 copy mapped via VMM into whatever process wants it. IIRC this was the main point of shared libraries, not pluggability or changing code during runtime. Am I missing something?
On top of what others have said, it takes some time to dynamically load a library into an address space. There are tables that may need to be walked and updated with correct pointers. For large libraries, this can be quite measurable. A statically linked executable will be memory-mapped and then brought in lazily as the program runs. And then if executed again, everything is mapped and loaded, so there is zero delay.…
True, but I'd expect that to be dwarfed by the I/O time required to load even a single 4k page from disk, vs. keeping one copy of a big dynamic library like glibc loaded for the whole system, with fixups done per-process.
Good points about ASLR and static-linking frequently-exec'd-and-exited processes like the shell; and certainly for embedded and HPC it makes sense. I guess the moral, as always, is to measure.