sysinfo: fix the unit of maxrss on FreeBSD

The value from rusage.ru_maxrss is in kilobytes.

Ref #22997
(cherry picked from commit f60636f)

base/sysinfo.jl

@@ -188,6 +188,14 @@ function set_process_title(title::AbstractString)
     Base.uv_error("set_process_title", err)
 end
 
+"""
+    Sys.maxrss()
+
+Get the maximum resident set size utilized in bytes.
+See also:
+    - man page of getrusage(2) on Linux and FreeBSD.
+    - windows api `GetProcessMemoryInfo`
+"""
 maxrss() = ccall(:jl_maxrss, Csize_t, ())
 
 if is_windows()

src/sys.c

@@ -776,11 +776,13 @@ JL_DLLEXPORT size_t jl_maxrss(void)
     GetProcessMemoryInfo( GetCurrentProcess( ), &counter, sizeof(counter) );
     return (size_t)counter.PeakWorkingSetSize;
 
+// FIXME: `rusage` is available on OpenBSD, DragonFlyBSD and NetBSD as well.
+//        All of them return `ru_maxrss` in kilobytes.
 #elif defined(_OS_LINUX_) || defined(_OS_DARWIN_) || defined (_OS_FREEBSD_)
     struct rusage rusage;
     getrusage( RUSAGE_SELF, &rusage );
 
-#if defined(_OS_LINUX_)
+#if defined(_OS_LINUX_) || defined(_OS_FREEBSD_)
     return (size_t)(rusage.ru_maxrss * 1024);
 #else
     return (size_t)rusage.ru_maxrss;