[Bug-time] GNU time reports incorrect maximum RSS

[Donald Buczek]

Hello,

we just learned the hard way about a bug in gnu time, that the maximum resident 
set size reported is scaled up by a factor 4, because the corresponding field 
the the rusage struct is wrongly interpreted as pages instead of kilobyte and 
scaled up on output.

This bug is 8 years old, and usually fixed by the distros, so distro-users 
don't see it. It has never been fixed in upstream, however. [1] [2]

The bug still exists in the master branch.

    $ curl -so mem.cpp https://ideone.com/plain/5bsp0R && make mem && /usr/bin/time -f 
"time thinks my peak rss is %M kB" ./mem
    g++     mem.cpp   -o mem
    procfs thinks my peak RSS is:       514652 kB
    time thinks my peak rss is 2058608 kB

The patch from [1] fixes the problem:

    address@hidden:~/time-rss$ /usr/bin/time -f "time thinks my peak rss is %M 
kB" ./mem
    procfs thinks my peak RSS is:       514616 kB
    time thinks my peak rss is 514616 kB

Thanks

  Donald

[1] https://bugzilla.redhat.com/show_bug.cgi?id=702826
[2] https://groups.google.com/forum/#!topic/gnu.utils.help/u1MOsHL4bhg


--
Donald Buczek
address@hidden
Tel: +49 30 8413 1433