OProfile Kernel Code Slated For Removal In Linux 5.12

OProfile as a system profiler for Linux systems was started twenty years ago during the Linux 2.4 kernel days. While the user-space components are still going strong, the kernel-side support is redundant in an era of the perf subsystem and thus slated for removal with Linux 5.12.

The OProfile user-space tools remain used and are still maintained (OProfile 1.4 came out last summer), but the kernel-side OProfile code is no longer needed since the user-space code has been refactored to make use of the Linux kernel's wonderful perf capabilities. Thus the kernel OProfile code has basically gone unused for quite a while unless running very vintage OProfile user-space tools.

Given that the OProfile tools have been making use of the kernel's perf interfaces, the kernel code is slated to be retired/eliminated with Linux 5.12. As part of the OProfile kernel code removal is also dropping of the "dcookies" file-system code that isn't used outside of OProfile in providing persistent cookie-path mappings.

Removing this obsolete code from the kernel clears up 15.5k lines of code. The removal is pending with this pull request.