this repurposes the memory usage fields in struct rusage to give the
current memory usage info when using getrusage(RUSAGE_SELF). this
is the same as what we can see in tools like top.

currently these fields are 0. they're documented as being max and some
integral values i dont understand. having the current values is better
than nothing.

im already using getrusage to collect metrics in some home grown
software, having current memory usage nicely complements the cpu
usage stats. some of these things run out of memory, so understanding
the trend over time will be useful.

fwiw, netbsd also uses the current values to populate these fields, but
didnt update their doco.

ok?

Index: lib/libc/sys/getrusage.2
===================================================================
RCS file: /cvs/src/lib/libc/sys/getrusage.2,v
diff -u -p -r1.18 getrusage.2
--- lib/libc/sys/getrusage.2	17 Jul 2024 13:29:05 -0000	1.18
+++ lib/libc/sys/getrusage.2	6 Dec 2024 05:21:51 -0000
@@ -64,10 +64,10 @@ the following structure:
 struct rusage {
         struct timeval ru_utime; /* user time used */
         struct timeval ru_stime; /* system time used */
-        long ru_maxrss;          /* max resident set size */
-        long ru_ixrss;           /* integral shared text memory size */
-        long ru_idrss;           /* integral unshared data size */
-        long ru_isrss;           /* integral unshared stack size */
+        long ru_maxrss;          /* resident set size */
+        long ru_ixrss;           /* shared text memory size */
+        long ru_idrss;           /* unshared data size */
+        long ru_isrss;           /* unshared stack size */
         long ru_minflt;          /* page reclaims */
         long ru_majflt;          /* page faults */
         long ru_nswap;           /* swaps */
@@ -89,22 +89,18 @@ the total amount of time spent executing
 the total amount of time spent in the system executing on behalf
 of the process(es).
 .It Fa ru_maxrss
-the maximum resident set size utilized (in kilobytes).
+the resident set size utilized (in kilobytes).
 .It Fa ru_ixrss
-an
-.Dq integral
-value indicating the amount of memory used
+a value indicating the amount of memory used
 by the text segment
 that was also shared among other processes.
-This value is expressed in units of kilobytes * ticks-of-execution.
+This value is expressed in units of kilobytes.
 .It Fa ru_idrss
-an integral value of the amount of unshared memory residing in the
-data segment of a process (expressed in units of
-kilobytes * ticks-of-execution).
+a value of the amount of unshared memory residing in the
+data segment of a process (expressed in units of kilobytes).
 .It Fa ru_isrss
-an integral value of the amount of unshared memory residing in the
-stack segment of a process (expressed in units of
-kilobytes * ticks-of-execution).
+a value of the amount of unshared memory residing in the
+stack segment of a process (expressed in units of kilobytes).
 .It Fa ru_minflt
 the number of page faults serviced without any I/O activity; here
 I/O activity is avoided by
Index: sys/sys/resource.h
===================================================================
RCS file: /cvs/src/sys/sys/resource.h,v
diff -u -p -r1.14 resource.h
--- sys/sys/resource.h	25 Oct 2013 04:42:48 -0000	1.14
+++ sys/sys/resource.h	6 Dec 2024 05:21:51 -0000
@@ -58,11 +58,11 @@
 struct	rusage {
 	struct timeval ru_utime;	/* user time used */
 	struct timeval ru_stime;	/* system time used */
-	long	ru_maxrss;		/* max resident set size */
+	long	ru_maxrss;		/* resident set size */
 #define	ru_first	ru_ixrss
-	long	ru_ixrss;		/* integral shared text memory size */
-	long	ru_idrss;		/* integral unshared data " */
-	long	ru_isrss;		/* integral unshared stack " */
+	long	ru_ixrss;		/* shared text memory size */
+	long	ru_idrss;		/* unshared data " */
+	long	ru_isrss;		/* unshared stack " */
 	long	ru_minflt;		/* page reclaims */
 	long	ru_majflt;		/* page faults */
 	long	ru_nswap;		/* swaps */
Index: sys/kern/kern_resource.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_resource.c,v
diff -u -p -r1.93 kern_resource.c
--- sys/kern/kern_resource.c	10 Nov 2024 06:45:36 -0000	1.93
+++ sys/kern/kern_resource.c	6 Dec 2024 05:21:51 -0000
@@ -542,6 +542,18 @@ sys_getrusage(struct proc *p, void *v, r
 	return (error);
 }
 
+static void
+ruspace(struct rusage *rup, struct proc *p)
+{
+	struct vmspace *vm = p->p_vmspace;
+
+	/* XXX these are all current values, not max or integrals */
+	rup->ru_maxrss = vm_resident_count(vm) << (PAGE_SHIFT - 10);
+	rup->ru_ixrss = vm->vm_tsize << (PAGE_SHIFT - 10);
+	rup->ru_idrss = vm->vm_dused << (PAGE_SHIFT - 10); /* vm_dsize too? */
+	rup->ru_isrss = vm->vm_ssize << (PAGE_SHIFT - 10);
+}
+
 int
 dogetrusage(struct proc *p, int who, struct rusage *rup)
 {
@@ -567,6 +579,7 @@ dogetrusage(struct proc *p, int who, str
 		}
 
 		calcru(&tu, &rup->ru_utime, &rup->ru_stime, NULL);
+		ruspace(rup, p);
 		break;
 
 	case RUSAGE_THREAD: