What's the unit of `ru_maxrss` on Linux?

Question

This is from man getrusage

struct rusage {
    struct timeval ru_utime; /* user time used */
    struct timeval ru_stime; /* system time used */         


        

Answer 1

The man page says:

ru_maxrss (since Linux 2.6.32)

This is the maximum resident set size used (in kilobytes). For RUSAGE_CHILDREN, this is the resident set size of the largest child, not the maximum resident set size of the process tree.

So, it's expressed in kilobytes, just like in BSD.

Answer 2

It's not a standard field for the rusage structure so POSIX doesn't mandate anything about it. But on Linux

ru_maxrss (since Linux 2.6.32)

This is the maximum resident set size used (in kilobytes). For RUSAGE_CHILDREN, this is the resident set size of the largest child, not the maximum resident set size of the process tree.