We have seen OS doing Copy on Write optimisation when forking a process. Reason being that most of the time fork is preceded by exec, so we don't want to incur the cost of page allocations and copying the data from the caller address space unnecessarily.
So does this also happen when doing CP on a linux with ext4 or xfs (journaling) file systems? If it does not happen, then why not?
Best Answer
The keyword to search is
reflink. It was recently implemented in XFS.EDIT: the XFS implementation was initially marked EXPERIMENTAL. This warning was removed in the kernel release 4.16, a number of months after I wrote the above :-).