Tianyang Li Tianyang Li - 13 days ago 5
C Question

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

This is from

man getrusage


struct rusage {
struct timeval ru_utime; /* user time used */
struct timeval ru_stime; /* system time used */
long ru_maxrss; /* maximum resident set size */
long ru_ixrss; /* integral shared memory size */
long ru_idrss; /* integral unshared data size */
long ru_isrss; /* integral unshared stack size */
long ru_minflt; /* page reclaims */
long ru_majflt; /* page faults */
long ru_nswap; /* swaps */
long ru_inblock; /* block input operations */
long ru_oublock; /* block output operations */
long ru_msgsnd; /* messages sent */
long ru_msgrcv; /* messages received */
long ru_nsignals; /* signals received */
long ru_nvcsw; /* voluntary context switches */
long ru_nivcsw; /* involuntary context switches */
};


However it's not specified what's the unit.

I saw FreeBSD's documentation which says it's in kilobytes, but I'm not sure about what unit it is on Linux.

Answer

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.