add option for OOM score adjustment

This commit adds a new --oom-score-adj option to start-stop-daemon and
supervise-daemon, as well as an equivalent SSD_OOM_SCORE_ADJ environment
variable. If either of these are specified (with the command-line
option taking precedence), then the specified adjustment value is
written to /proc/self/oom_score_adj after forking but prior to exec'ing
the daemon (at the time when nice and ionice are applied).

Additionally, per a suggestion by Mike Frysinger, the suggested values
for the SSD_NICELEVEL, SSD_IONICELEVEL, and SSD_OOM_SCORE_ADJ variables
in the example config file are now given as zeros, which are the
kernel's default values of these process knobs for the init process at
boot. Note that uncommenting any of these zero-valued suggestions will
cause SSD/SD to set the corresponding process knob affirmatively to
zero, whereas leaving the variable unset (and the equivalent command-
line option unspecified) means SSD/SD will not change the corresponding
process knob from its inherited value.

See: https://github.com/OpenRC/openrc/pull/435#discussion_r688310672
This fixes #435.

etc/rc.conf

@@ -116,10 +116,12 @@
 
 # Some daemons are started and stopped via start-stop-daemon.
 # We can set some things on a per service basis, like the nicelevel.
-#SSD_NICELEVEL="-19"
+#SSD_NICELEVEL="0"
 # Or the ionice level. The format is class[:data] , just like the
 # --ionice start-stop-daemon parameter.
-#SSD_IONICELEVEL="2:2"
+#SSD_IONICELEVEL="0:0"
+# Or the OOM score adjustment.
+#SSD_OOM_SCORE_ADJ="0"
 
 # Pass ulimit parameters
 # If you are using bash in POSIX mode for your shell, note that the

man/start-stop-daemon.8

@@ -128,6 +128,8 @@ Class can be 0 for none, 1 for real time, 2 for best effort and 3 for idle.
 Data can be from 0 to 7 inclusive.
 .It Fl N , -nicelevel Ar level
 Modifies the scheduling priority of the daemon.
+.It Fl -oom-score-adj Ar adj
+Modifies the OOM score adjustment of the daemon.
 .It Fl 1 , -stdout Ar logfile
 Redirect the standard output of the process to logfile when started with
 .Fl background .
@@ -187,6 +189,10 @@ option takes precedence.
 can also set the scheduling priority of the daemon, but the command line
 option takes precedence.
 .Pp
+.Va SSD_OOM_SCORE_ADJ
+can also set the OOM score adjustment of the daemon, but the command line
+option takes precedence.
+.Pp
 .Va SSD_STARTWAIT
 As the
 .Fl w , -wait option above.

man/supervise-daemon.8

@@ -37,6 +37,8 @@ servicename
 .Ar count
 .Fl N , -nicelevel
 .Ar level
+.Fl -oom-score-adj
+.Ar adj
 .Fl p , -pidfile
 .Ar supervisorpidfile
 .Fl P , -respawn-period
@@ -129,6 +131,8 @@ Sets a path for the supervisor's pid file. Note that this is not the pid
 file of the process that is being supervised.
 .It Fl N , -nicelevel Ar level
 Modifies the scheduling priority of the daemon.
+.It Fl -oom-score-adj Ar adj
+Modifies the OOM score adjustment of the daemon.
 .It Fl P , -respawn-period Ar seconds
 Sets the length of a respawn period. See the
 description of --respawn-max for more information.
@@ -163,6 +167,10 @@ option takes precedence.
 .Va SSD_NICELEVEL
 can also set the scheduling priority of the daemon, but the command line
 option takes precedence.
+.Pp
+.Va SSD_OOM_SCORE_ADJ
+can also set the OOM score adjustment of the daemon, but the command line
+option takes precedence.
 .Sh NOTE
 .Nm
 uses

src/rc/start-stop-daemon.c

@@ -72,6 +72,7 @@ const struct option longopts[] = {
 	{ "ionice",       1, NULL, 'I'},
 	{ "stop",         0, NULL, 'K'},
 	{ "nicelevel",    1, NULL, 'N'},
+	{ "oom-score-adj",1, NULL,0x80},
 	{ "retry",        1, NULL, 'R'},
 	{ "start",        0, NULL, 'S'},
 	{ "startas",      1, NULL, 'a'},
@@ -103,6 +104,7 @@ const char * const longopts_help[] = {
 	"Set an ionice class:data when starting",
 	"Stop daemon",
 	"Set a nicelevel when starting",
+	"Set OOM score adjustment when starting",
 	"Retry schedule to use when stopping",
 	"Start daemon",
 	"deprecated, use --exec or --name",
@@ -270,7 +272,8 @@ int main(int argc, char **argv)
 	char *pidfile = NULL;
 	char *retry = NULL;
 	int sig = -1;
-	int nicelevel = 0, ionicec = -1, ioniced = 0;
+	int nicelevel = INT_MIN, ionicec = -1, ioniced = 0;
+	int oom_score_adj = INT_MIN;
 	bool background = false;
 	bool makepidfile = false;
 	bool interpreted = false;
@@ -327,6 +330,10 @@ int main(int argc, char **argv)
 			ioniced = 7;
 		ionicec <<= 13; /* class shift */
 	}
+	if ((tmp = getenv("SSD_OOM_SCORE_ADJ")))
+		if (sscanf(tmp, "%d", &oom_score_adj) != 1)
+			eerror("%s: invalid oom_score_adj `%s' (SSD_OOM_SCORE_ADJ)",
+			    applet, tmp);
 
 	/* Get our user name and initial dir */
 	p = getenv("USER");
@@ -367,6 +374,12 @@ int main(int argc, char **argv)
 				    applet, optarg);
 			break;
 
+		case 0x80: /* --oom-score-adj */
+			if (sscanf(optarg, "%d", &oom_score_adj) != 1)
+				eerrorx("%s: invalid oom-score-adj `%s'",
+				    applet, optarg);
+			break;
+
 		case 'P':  /* --progress */
 			progress = true;
 			break;
@@ -778,7 +791,7 @@ int main(int argc, char **argv)
 
 		devnull_fd = open("/dev/null", O_RDWR);
 
-		if (nicelevel) {
+		if (nicelevel != INT_MIN) {
 			if (setpriority(PRIO_PROCESS, mypid, nicelevel) == -1)
 				eerrorx("%s: setpriority %d: %s",
 				    applet, nicelevel,
@@ -790,6 +803,15 @@ int main(int argc, char **argv)
 			eerrorx("%s: ioprio_set %d %d: %s", applet,
 			    ionicec, ioniced, strerror(errno));
 
+		if (oom_score_adj != INT_MIN) {
+			fp = fopen("/proc/self/oom_score_adj", "w");
+			if (!fp)
+				eerrorx("%s: oom_score_adj %d: %s", applet,
+				    oom_score_adj, strerror(errno));
+			fprintf(fp, "%d\n", oom_score_adj);
+			fclose(fp);
+		}
+
 		if (ch_root && chroot(ch_root) < 0)
 			eerrorx("%s: chroot `%s': %s",
 			    applet, ch_root, strerror(errno));
@@ -867,7 +889,8 @@ int main(int argc, char **argv)
 				strncmp(env->value, "RC_SERVICE=", 11) != 0 &&
 				strncmp(env->value, "RC_SVCNAME=", 11) != 0) ||
 				strncmp(env->value, "SSD_NICELEVEL=", 14) == 0 ||
-				strncmp(env->value, "SSD_IONICELEVEL=", 16) == 0)
+				strncmp(env->value, "SSD_IONICELEVEL=", 16) == 0 ||
+				strncmp(env->value, "SSD_OOM_SCORE_ADJ=", 18) == 0)
 			{
 				p = strchr(env->value, '=');
 				*p = '\0';

src/rc/supervise-daemon.c

@@ -82,6 +82,7 @@ const struct option longopts[] = {
 	{ "umask",        1, NULL, 'k'},
 	{ "respawn-max",    1, NULL, 'm'},
 	{ "nicelevel",    1, NULL, 'N'},
+	{ "oom-score-adj",1, NULL,0x80},
 	{ "pidfile",      1, NULL, 'p'},
 	{ "respawn-period",        1, NULL, 'P'},
 	{ "retry",       1, NULL, 'R'},
@@ -106,6 +107,7 @@ const char * const longopts_help[] = {
 	"Set the umask for the daemon",
 	"set maximum number of respawn attempts",
 	"Set a nicelevel when starting",
+	"Set OOM score adjustment when starting",
 	"Match pid found in this file",
 	"Set respawn time period",
 	"Retry schedule to use when stopping",
@@ -124,9 +126,10 @@ static int healthcheckdelay = 0;
 static int healthchecktimer = 0;
 static volatile sig_atomic_t do_healthcheck = 0;
 static volatile sig_atomic_t exiting = 0;
-static int nicelevel = 0;
+static int nicelevel = INT_MIN;
 static int ionicec = -1;
 static int ioniced = 0;
+static int oom_score_adj = INT_MIN;
 static char *changeuser, *ch_root, *ch_dir;
 static uid_t uid = 0;
 static gid_t gid = 0;
@@ -332,6 +335,7 @@ static void child_process(char *exec, char **argv)
 	time_t start_time;
 	char start_count_string[20];
 	char start_time_string[20];
+	FILE *fp;
 
 #ifdef HAVE_PAM
 	pam_handle_t *pamh = NULL;
@@ -351,7 +355,7 @@ static void child_process(char *exec, char **argv)
 		rc_service_value_set(svcname, "child_pid", start_count_string);
 	}
 
-	if (nicelevel) {
+	if (nicelevel != INT_MIN) {
 		if (setpriority(PRIO_PROCESS, getpid(), nicelevel) == -1)
 			eerrorx("%s: setpriority %d: %s", applet, nicelevel,
 					strerror(errno));
@@ -361,6 +365,15 @@ static void child_process(char *exec, char **argv)
 		eerrorx("%s: ioprio_set %d %d: %s", applet, ionicec, ioniced,
 				strerror(errno));
 
+	if (oom_score_adj != INT_MIN) {
+		fp = fopen("/proc/self/oom_score_adj", "w");
+		if (!fp)
+			eerrorx("%s: oom_score_adj %d: %s", applet,
+			    oom_score_adj, strerror(errno));
+		fprintf(fp, "%d\n", oom_score_adj);
+		fclose(fp);
+	}
+
 	if (ch_root && chroot(ch_root) < 0)
 		eerrorx("%s: chroot `%s': %s", applet, ch_root, strerror(errno));
 
@@ -424,7 +437,8 @@ static void child_process(char *exec, char **argv)
 			strncmp(env->value, "RC_SERVICE=", 11) != 0 &&
 			strncmp(env->value, "RC_SVCNAME=", 11) != 0) ||
 		    strncmp(env->value, "SSD_NICELEVEL=", 14) == 0 ||
-		    strncmp(env->value, "SSD_IONICELEVEL=", 16) == 0)
+		    strncmp(env->value, "SSD_IONICELEVEL=", 16) == 0 ||
+		    strncmp(env->value, "SSD_OOM_SCORE_ADJ=", 18) == 0)
 		{
 			p = strchr(env->value, '=');
 			*p = '\0';
@@ -745,6 +759,10 @@ int main(int argc, char **argv)
 			ioniced = 7;
 		ionicec <<= 13; /* class shift */
 	}
+	if ((tmp = getenv("SSD_OOM_SCORE_ADJ")))
+		if (sscanf(tmp, "%d", &oom_score_adj) != 1)
+			eerror("%s: invalid oom_score_adj `%s' (SSD_OOM_SCORE_ADJ)",
+			    applet, tmp);
 
 	/* Get our user name and initial dir */
 	p = getenv("USER");
@@ -806,6 +824,12 @@ int main(int argc, char **argv)
 				    applet, optarg);
 			break;
 
+		case 0x80: /* --oom-score-adj */
+			if (sscanf(optarg, "%d", &oom_score_adj) != 1)
+				eerrorx("%s: invalid oom-score-adj `%s'",
+				    applet, optarg);
+			break;
+
 		case 'P':  /* --respawn-period time */
 			n = sscanf(optarg, "%d", &respawn_period);
 			if (n	!= 1 || respawn_period < 1)