[PATCH] support for panic at OOM

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

This patch adds a feature to panic at OOM, oom_die.

When sysctl vm.oom_die = 1, the kernel panics intead of killing
rogue processes. And if vm.oom_die is 0 the kernel will do
oom_kill() in the same way as it does today. Of course, the 
default value is 0 and only root can modifies it.

In general, oom_killer works well and kill rogue processes. So 
the whole system can survive. But there are environments where
panic is preferable rather than kill some processes.

For example, a failover system can replace a broken system with
back-up system immediately at panic, so it doesn't need oom_kill.

Considering a failover cluster system, a failover service puts
all nodes under its observation. When a node panics, the failover
system  can replace it with new one immediately. But if oom_kill runs
and kills some processes, the system will go to partial broken
state. This partial broken state is sometimes difficult to be
detected. The worst case is that a failover daemon is killed 
(possibility is not 0%), the whole system will be unstable.

Another case is crash-dump supported system. If the system panics
at OOM, crash dump can preserve *all* information about system.
Because SIGKILL cannot cause process coredump, oom killer cannot
preserve any hints except for the message log.

thanks,
-Kame
==

This patch adds oom_die sysctl under sys.vm.

When oom_die==1, system panic at out_of_memory istead of kill some
process. In some situation, I think panic is more useful than kill.
This patch is against 2.6.17-rc1-mm2.

Signed-Off-By: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Index: linux-2.6.17-rc1-mm2/kernel/sysctl.c
===================================================================
--- linux-2.6.17-rc1-mm2.orig/kernel/sysctl.c
+++ linux-2.6.17-rc1-mm2/kernel/sysctl.c
@@ -60,6 +60,7 @@ extern int proc_nr_files(ctl_table *tabl
 extern int C_A_D;
 extern int sysctl_overcommit_memory;
 extern int sysctl_overcommit_ratio;
+extern int sysctl_oom_die;
 extern int max_threads;
 extern int sysrq_enabled;
 extern int core_uses_pid;
@@ -718,6 +719,14 @@ static ctl_table vm_table[] = {
 		.proc_handler	= &proc_dointvec,
 	},
 	{
+		.ctl_name	= VM_OOM_DIE,
+		.procname	= "oom_die",
+		.data		= &sysctl_oom_die,
+		.maxlen		= sizeof(sysctl_oom_die),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec,
+	},
+	{
 		.ctl_name	= VM_OVERCOMMIT_RATIO,
 		.procname	= "overcommit_ratio",
 		.data		= &sysctl_overcommit_ratio,
Index: linux-2.6.17-rc1-mm2/mm/oom_kill.c
===================================================================
--- linux-2.6.17-rc1-mm2.orig/mm/oom_kill.c
+++ linux-2.6.17-rc1-mm2/mm/oom_kill.c
@@ -23,7 +23,7 @@
 #include <linux/cpuset.h>
 
 /* #define DEBUG */
-
+int sysctl_oom_die = 0;
 /**
  * oom_badness - calculate a numeric value for how bad this task has been
  * @p: task struct of which task we should calculate
@@ -290,6 +290,12 @@ static struct mm_struct *oom_kill_proces
 	return oom_kill_task(p, message);
 }
 
+
+static void oom_die(void)
+{
+	panic("Panic: out of memory: oom_die is selected.");
+}
+
 /**
  * oom_kill - kill the "best" process when we run out of memory
  *
@@ -331,6 +337,8 @@ void out_of_memory(struct zonelist *zone
 
 	case CONSTRAINT_NONE:
 retry:
+		if (sysctl_oom_die)
+			oom_die();
 		/*
 		 * Rambo mode: Shoot down a process and hope it solves whatever
 		 * issues we may have.

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