The kernel doesn't have to know the current directory's path. It's enough that it know -and retain an open file reference to- the current directory's inode/dno

The kernel doesn't have to know the current directory's path. It's enough that it know -and retain an open file reference to- the current directory's inode/dnode. However, if you want things like DTrace, eBPF, or even just reading the /proc/PID/cwd symlink to be useful, it helps to cache the actual path in the kernel. A DTrace/eBPF script will not be able to loop to chase ..s, much less will it be able to do the I/O needed to work out the cwd. The same applies to the names of the files that each FD refer to. Caching these things is just for observability.