mark.  This struct is filled as a parameter to getrusage syscall. 
->ru_maxrss value is set to KBs which is the way it is done in BSD
systems.  /usr/bin/time (gnu time) application converts ->ru_maxrss to KBs
which seems to be incorrect behavior.  Maintainer of this util was
notified by me with the patch which corrects it and cc'ed.

To make this happen we extend struct signal_struct by two fields.  The
first one is ->maxrss which we use to store rss hiwater of the task.  The
second one is ->cmaxrss which we use to store highest rss hiwater of all
task childs.  These values are used in k_getrusage() to actually fill
->ru_maxrss.  k_getrusage() uses current rss hiwater value directly if mm
struct exists.

Note:
exec() clear mm->hiwater_rss, but doesn't clear sig->maxrss.
it is intetionally behavior. *BSD getrusage have exec() inheriting.

Test progmam and test case
===========================

getrusage.c
====
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <signal.h>

static void consume(int mega)
{
	size_t sz = mega * 1024 * 1024;
	void *ptr;

	ptr = malloc(sz);
	memset(ptr, 0, sz);
	usleep(1);  /* BSD rusage statics need to sleep 1 tick */
}

static void show_rusage(char *prefix)
{
	int err, err2;
	struct rusage rusage_self;
	struct rusage rusage_children;

	printf("%s: ", prefix);
	err = getrusage(RUSAGE_SELF, &rusage_self);
	if (!err)
		printf("self %ld ", rusage_self.ru_maxrss);
	err2 = getrusage(RUSAGE_CHILDREN, &rusage_children);
	if (!err2)
		printf("children %ld ", rusage_children.ru_maxrss);

	printf("\n");
}

int main(int argc, char** argv)
{
	int status;
	int c;
	int need_sleep_before_wait = 0;
	int consume_large_memory_at_first = 0;
	int create_child_at_first = 0;
	int sigign = 0;
	int create_child_before_exec = 0;
	int after_fork_test = 0;

	while ((c = getopt(argc, argv, "ceflsz")) != -1) {
		switch (c) {
		case 'c':
			create_child_at_first = 1;
			break;
		case 'e':
			create_child_before_exec = 1;
			break;
		case 'f':
			after_fork_test = 1;
			break;
		case 'l':
			consume_large_memory_at_first = 1;
			break;
		case 's':
			sigign = 1;
			break;
		case 'z':
			need_sleep_before_wait = 1;
			break;
		default:
			break;
		}
	}

	if (consume_large_memory_at_first)
		consume(100);

	if (create_child_at_first)
		system("./child -q");

	if (sigign)
		signal(SIGCHLD, SIG_IGN);

	if (fork()) {
		usleep(1);
		if (need_sleep_before_wait)
			sleep(3); /* children become zombie */
		show_rusage("pre_wait");
		wait(&status);
		show_rusage("post_wait");
	} else {
		usleep(1);
		show_rusage("fork");

		if (after_fork_test) {
			consume(30);
			show_rusage("fork2");
		}
		if (create_child_before_exec) {
			system("./child -lq");
			usleep(1);
			show_rusage("fork3");
		}

		execl("./child", "child", 0);
		exit(0);
	}

	return 0;
}

child.c
====
#include <sys/types.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/resource.h>

static void consume(int mega)
{
	size_t sz = mega * 1024 * 1024;
	void *ptr;

	ptr = malloc(sz);
	memset(ptr, 0, sz);
	usleep(1);  /* BSD rusage statics need to sleep 1 tick */
}

static void show_rusage(char *prefix)
{
	int err, err2;
	struct rusage rusage_self;
	struct rusage rusage_children;

	printf("%s: ", prefix);
	err = getrusage(RUSAGE_SELF, &rusage_self);
	if (!err)
		printf("self %ld ", rusage_self.ru_maxrss);
	err2 = getrusage(RUSAGE_CHILDREN, &rusage_children);
	if (!err2)
		printf("children %ld ", rusage_children.ru_maxrss);

	printf("\n");

}

int main(int argc, char** argv)
{
	int status;
	int c;
	int silent = 0;
	int light_weight = 0;

	while ((c = getopt(argc, argv, "lq")) != -1) {
		switch (c) {
		case 'l':
			light_weight = 1;
			break;
		case 'q':
			silent = 1;
			break;
		default:
			break;
		}
	}

	if (!silent)
		show_rusage("exec");

	if (fork()) {
		if (light_weight)
			consume(400);
		else
			consume(700);
		wait(&status);
	} else {
		if (light_weight)
			consume(600);
		else
			consume(900);

		exit(0);
	}

	return 0;
}

testcase
========

1. inherit fork?

   test way:
   	% ./getrusage -lc

   bsd result:
   	fork line is "fork: self 0 children 0".

   	-> rusage sholdn't be inherit by fork.
	   (both RUSAGE_SELF and RUSAGE_CHILDREN)

2. inherit exec?

   test way:
   	% ./getrusage -lce

   bsd result:
   	fork3: self 103204 children 60000
	exec: self 103204 children 60000

   	fork3 and exec line are the same.

   	-> rusage shold be inherit by exec.
	   (both RUSAGE_SELF and RUSAGE_CHILDREN)

3. getrusage(RUSAGE_CHILDREN) collect grandchild statics?

   test way:
   	% ./getrusage

   bsd result:
   	post_wait line is about "post_wait: self 0 children 90000".

	-> RUSAGE_CHILDREN can collect grandchild.

4. zombie, but not waited children collect or not?

   test way:
   	% ./getrusage -z

   bsd result:
   	pre_wait line is "pre_wait: self 0 children 0".

	-> zombie child process (not waited-for child process)
	   isn't accounted.

5. SIG_IGN collect or not

   test way:
   	% ./getrusage -s

   bsd result:
   	post_wait line is "post_wait: self 0 children 0".

	-> if SIGCHLD is ignored, children isn't accounted.

6. fork and malloc
   test way:
   	% ./getrusage -lcf

   bsd result:
   	fork line is "fork: self 0 children 0".
   	fork2 line is about "fork: self 130000 children 0".

   	-> rusage sholdn't be inherit by fork.
	   (both RUSAGE_SELF and RUSAGE_CHILDREN)
	   but additional memory cunsumption cause right
	   maxrss calculation.
Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>