Re: [RFC] Enabling other oom schemes

From: Rusty Lynch
Date: Fri Sep 12 2003 - 21:25:38 EST

On Fri, 2003-09-12 at 01:58, Tvrtko A. UrÅulin wrote:
>
> > * Added a very simple (in fact I'm sure too simple) mm/om_panic.c that
> > will panic on any oom condition
> >
> > The patch works (although by looking over oom_kill.c, I'm sure oom_panic.c
> > will panic too soon), but it is really only a quick hack to see how people
> > feel about such an approach.
>
> I like it, but who am I to say... No so long ago I made a patch for 2.4.20
> (attached) which extended OOM Killer functionality in a following way: If a
> process of the same parent gets killed more than X times during Y seconds,
> parent gets killed.
>
> Maybe this kind of module for your patch would be interesting for someone?
>
> Regards,
> Tvrtko


I went ahead and added a new oom handler that is a combination of
the original oom_kill.c combined with the changes from Tvrtko's patch
(originally written for 2.4.20) that kills off parents that keep producing
bad children. It sounds a little right wing, but it works :->

Just walking around cube-ville I'm hearing lots of cool ideas for little oom
handlers. I know in past project where I was attempting to cram mozilla
into a resource deprived TV set-top box, I would have loved to have an oom
handler that always blamed mozilla (since it leaked like a sieve and was
constantly a pain in my ass) and nothing else.

--rustyl

# This is a BitKeeper generated patch for the following project:
# Project Name: Linux kernel tree
# This patch format is intended for GNU patch command version 2.5 or higher.
# This patch includes the following deltas:
# ChangeSet 1.1283.1.32 -> 1.1287
# kernel/sysctl.c 1.53 -> 1.54
# mm/oom_kill.c 1.24 -> 1.25
# include/linux/sysctl.h 1.51 -> 1.52
# mm/Makefile 1.24 -> 1.26
# init/Kconfig 1.28 -> 1.30
# (new) -> 1.1 mm/oom_panic.c
# (new) -> 1.1 mm/oom_notifier.c
# (new) -> 1.1 mm/oom_kill_parent.c
#
# The following is the BitKeeper ChangeSet Log
# --------------------------------------------
# 03/09/12 rusty@xxxxxxxxxxxxxxxxxxxx 1.1286
# Merge http://linux.bkbits.net:8080/linux-2.5
# into penguin.co.intel.com:/src/linux/linus
# --------------------------------------------
# 03/09/12 rusty@xxxxxxxxxxxxxxxxxxxx 1.1287
# Adding OOM handler that kills parents that produce bad children
# --------------------------------------------
#
diff -Nru a/include/linux/notifier.h b/include/linux/notifier.h
--- a/include/linux/notifier.h Fri Sep 12 18:59:35 2003
+++ b/include/linux/notifier.h Fri Sep 12 18:59:35 2003
@@ -66,5 +66,7 @@
#define CPU_OFFLINE 0x0005 /* CPU (unsigned)v offline (still scheduling) */
#define CPU_DEAD 0x0006 /* CPU (unsigned)v dead */

+#define OUT_OF_MEMORY 0x00007 /* Notify of critical memory shortage */
+
#endif /* __KERNEL__ */
#endif /* _LINUX_NOTIFIER_H */
diff -Nru a/include/linux/oom_notifier.h b/include/linux/oom_notifier.h
--- /dev/null Wed Dec 31 16:00:00 1969
+++ b/include/linux/oom_notifier.h Fri Sep 12 18:59:35 2003
@@ -0,0 +1,7 @@
+#ifndef _LINUX_OOM_NOTIFIER_H
+#define _LINUX_OOM_NOTIFIER_H
+
+int register_oom_notifier(struct notifier_block * nb);
+int unregister_oom_notifier(struct notifier_block * nb);
+
+#endif /* _LINUX_OOM_NOTIFIER_H */
diff -Nru a/include/linux/sysctl.h b/include/linux/sysctl.h
--- a/include/linux/sysctl.h Fri Sep 12 18:59:35 2003
+++ b/include/linux/sysctl.h Fri Sep 12 18:59:35 2003
@@ -154,6 +154,8 @@
VM_SWAPPINESS=19, /* Tendency to steal mapped memory */
VM_LOWER_ZONE_PROTECTION=20,/* Amount of protection of lower zones */
VM_MIN_FREE_KBYTES=21, /* Minimum free kilobytes to maintain */
+ VM_OOM_PARENT_MAX=22,
+ VM_OOM_PARENT_EXPIRE=23,
};


diff -Nru a/init/Kconfig b/init/Kconfig
--- a/init/Kconfig Fri Sep 12 18:59:35 2003
+++ b/init/Kconfig Fri Sep 12 18:59:35 2003
@@ -162,6 +162,33 @@
This option enables access to kernel configuration file and build
information through /proc/config.gz.

+config OOM_KILL
+ bool "Kill process on out-of-memory conditions"
+ ---help---
+ This option enables the traditional oom_kill.c mechanism for
+ killing processes in an attempt to recover from an out-of-memory
+ condition.
+
+config OOM_PANIC
+ tristate "Panic on out-of-memory conditions"
+ ---help---
+ This option enables panic() to be called when a system is out of
+ memory. This feature along with /proc/sys/kernel/panic allows a
+ different behavior on out-of-memory conditions when the standard
+ behavior (killing processes in an attempt to recover) does not
+ make sense.
+
+config OOM_KPPID
+ bool "Kill bad parents along with their children when out-of-memory"
+ ---help---
+ This option enables an out-of-memory handler that not only attempts
+ to kill bad processes to free up memory, but also kills parents
+ that repeatedly produce bad children.
+
+ Two tunables, oom_parent_max and oom_parent_expire, will be added
+ and to /proc/sys/vm/ to control how many children a parent is
+ allowed to have terminated, and how long between terminated children
+ before a parent is forgiven.

menuconfig EMBEDDED
bool "Remove kernel features (for embedded systems)"
diff -Nru a/kernel/sysctl.c b/kernel/sysctl.c
--- a/kernel/sysctl.c Fri Sep 12 18:59:35 2003
+++ b/kernel/sysctl.c Fri Sep 12 18:59:35 2003
@@ -59,6 +59,8 @@
extern int pid_max;
extern int sysctl_lower_zone_protection;
extern int min_free_kbytes;
+extern unsigned int oom_parent_max;
+extern unsigned int oom_parent_expire;

/* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
static int maxolduid = 65535;
@@ -672,6 +674,24 @@
.extra1 = &zero,
.extra2 = &one_hundred,
},
+#ifdef CONFIG_OOM_KPPID
+ {
+ .ctl_name = VM_OOM_PARENT_MAX,
+ .procname = "oom_parent_max",
+ .data = &oom_parent_max,
+ .maxlen = sizeof(oom_parent_max),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
+ {
+ .ctl_name = VM_OOM_PARENT_EXPIRE,
+ .procname = "oom_parent_expire",
+ .data = &oom_parent_expire,
+ .maxlen = sizeof(oom_parent_expire),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
+#endif
#ifdef CONFIG_HUGETLB_PAGE
{
.ctl_name = VM_HUGETLB_PAGES,
diff -Nru a/mm/Makefile b/mm/Makefile
--- a/mm/Makefile Fri Sep 12 18:59:35 2003
+++ b/mm/Makefile Fri Sep 12 18:59:35 2003
@@ -7,8 +7,12 @@
mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \
shmem.o vmalloc.o

-obj-y := bootmem.o filemap.o mempool.o oom_kill.o fadvise.o \
+obj-y := bootmem.o filemap.o mempool.o fadvise.o \
page_alloc.o page-writeback.o pdflush.o readahead.o \
- slab.o swap.o truncate.o vmscan.o $(mmu-y)
+ slab.o swap.o truncate.o vmscan.o oom_notifier.o \
+ $(mmu-y)

obj-$(CONFIG_SWAP) += page_io.o swap_state.o swapfile.o
+obj-$(CONFIG_OOM_PANIC) += oom_panic.o
+obj-$(CONFIG_OOM_KILL) += oom_kill.o
+obj-$(CONFIG_OOM_KPPID) += oom_kill_parent.o
diff -Nru a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c Fri Sep 12 18:59:35 2003
+++ b/mm/oom_kill.c Fri Sep 12 18:59:35 2003
@@ -20,6 +20,10 @@
#include <linux/swap.h>
#include <linux/timex.h>
#include <linux/jiffies.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/notifier.h>
+#include <linux/oom_notifier.h>

/* #define DEBUG */

@@ -230,7 +234,7 @@
/**
* out_of_memory - is the system out of memory?
*/
-void out_of_memory(void)
+static void out_of_memory_killer(void)
{
/*
* oom_lock protects out_of_memory()'s static variables.
@@ -305,3 +309,20 @@
out_unlock:
spin_unlock(&oom_lock);
}
+
+static int oom_notify(struct notifier_block * s, unsigned long v, void * d)
+{
+ out_of_memory_killer();
+ return 0;
+}
+
+static struct notifier_block oom_nb = {
+ .notifier_call = oom_notify,
+};
+
+static int __init init_oom_kill(void)
+{
+ printk("Registering oom_kill handler\n");
+ return register_oom_notifier(&oom_nb);
+}
+module_init(init_oom_kill);
diff -Nru a/mm/oom_kill_parent.c b/mm/oom_kill_parent.c
--- /dev/null Wed Dec 31 16:00:00 1969
+++ b/mm/oom_kill_parent.c Fri Sep 12 18:59:35 2003
@@ -0,0 +1,435 @@
+/*
+ * linux/mm/oom_kill_parent.c
+ *
+ * Copyright (C) 1998,2000 Rik van Riel
+ * Copyright (C) 2003 Tvrtko A. Ursulin (tvrtko.ursulin@xxxxxxxxxxx)
+ *
+ * Based on the original linux/mm/oom_kill.c combined with a patch
+ * submitted to LKML by Tvrtko A. Ursulin that would kill parents
+ * that continue to produce bad children.
+ * --rustyl <rusty@xxxxxxxxxxxxxxx>
+ */
+
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/swap.h>
+#include <linux/timex.h>
+#include <linux/jiffies.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/notifier.h>
+#include <linux/oom_notifier.h>
+
+#define OOM_BLACK_LIST_SIZE 32
+#define OOM_DEFAULT_VALUE (10)
+#define OOM_DEFAULT_EXPIRE (5*60)
+
+struct parent_record
+{
+ pid_t pid;
+ struct task_struct *task;
+ unsigned long last_kill;
+ unsigned long value;
+};
+
+unsigned int oom_parent_max = OOM_DEFAULT_VALUE;
+unsigned int oom_parent_expire = OOM_DEFAULT_EXPIRE;
+
+static struct parent_record black_list[OOM_BLACK_LIST_SIZE];
+
+#define DEBUG 1
+
+#ifdef DEBUG
+#define dbg(format, arg...) \
+ do { \
+ printk (KERN_DEBUG "OOM: " format "\n", \
+ ## arg); \
+ } while(0)
+#else
+#define dbg(format, arg...)
+#endif
+#define warn(format, arg...) \
+ do { \
+ printk (KERN_WARNING "OOM: " format "\n", \
+ ## arg); \
+ } while(0)
+#define error(format, arg...) \
+ do { \
+ printk (KERN_ERR "Out-of-Memory: " format "\n", \
+ ## arg); \
+ } while(0)
+
+static struct parent_record *find_in_black_list(struct task_struct *task)
+{
+ struct parent_record *p = NULL;
+ unsigned int i;
+
+ if ( !task )
+ return NULL;
+
+ for ( i = 0; i < OOM_BLACK_LIST_SIZE; i++ ) {
+ p = &black_list[i];
+ if ( p->pid )
+ if ( (task->pid == p->pid) && (task == p->task) )
+ return p;
+ }
+
+ return NULL;
+}
+
+static void black_list_parent(struct task_struct *task)
+{
+ struct parent_record *p;
+ int i;
+
+ if ( !task && !task->parent )
+ return;
+
+ for ( i = 0; i < OOM_BLACK_LIST_SIZE; i++ ) {
+ p = &black_list[i];
+ if ( !p->pid )
+ break;
+ }
+ if (p->pid) {
+ dbg("black list is full... %d is getting off easy",
+ task->parent->pid);
+ return;
+ }
+ p->pid= task->parent->pid;
+ p->task = task->parent;
+ p->last_kill = jiffies;
+ p->value = 0;
+
+ return;
+}
+
+/**
+ * int_sqrt - oom_kill.c internal function, rough approximation to sqrt
+ * @x: integer of which to calculate the sqrt
+ *
+ * A very rough approximation to the sqrt() function.
+ */
+static unsigned int int_sqrt(unsigned int x)
+{
+ unsigned int out = x;
+ while (x & ~(unsigned int)1) x >>=2, out >>=1;
+ if (x) out -= out >> 2;
+ return (out ? out : 1);
+}
+
+/**
+ * oom_badness - calculate a numeric value for how bad this task has been
+ * @p: task struct of which task we should calculate
+ *
+ * The formula used is relatively simple and documented inline in the
+ * function. The main rationale is that we want to select a good task
+ * to kill when we run out of memory.
+ *
+ * Good in this context means that:
+ * 1) we lose the minimum amount of work done
+ * 2) we recover a large amount of memory
+ * 3) we don't kill anything innocent of eating tons of memory
+ * 4) we want to kill the minimum amount of processes (one)
+ * 5) we try to kill the process the user expects us to kill, this
+ * algorithm has been meticulously tuned to meet the principle
+ * of least surprise ... (be careful when you change it)
+ */
+
+static int badness(struct task_struct *p)
+{
+ int points, cpu_time, run_time;
+
+ if (!p->mm)
+ return 0;
+
+ if (p->flags & PF_MEMDIE)
+ return 0;
+ /*
+ * The memory size of the process is the basis for the badness.
+ */
+ points = p->mm->total_vm;
+
+ /*
+ * CPU time is in seconds and run time is in minutes. There is no
+ * particular reason for this other than that it turned out to work
+ * very well in practice.
+ */
+ cpu_time = (p->utime + p->stime) >> (SHIFT_HZ + 3);
+ run_time = (get_jiffies_64() - p->start_time) >> (SHIFT_HZ + 10);
+
+ points /= int_sqrt(cpu_time);
+ points /= int_sqrt(int_sqrt(run_time));
+
+ /*
+ * Niced processes are most likely less important, so double
+ * their badness points.
+ */
+ if (task_nice(p) > 0)
+ points *= 2;
+
+ /*
+ * Superuser processes are usually more important, so we make it
+ * less likely that we kill those.
+ */
+ if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||
+ p->uid == 0 || p->euid == 0)
+ points /= 4;
+
+ /*
+ * We don't want to kill a process with direct hardware access.
+ * Not only could that mess up the hardware, but usually users
+ * tend to only have this flag set on applications they think
+ * of as important.
+ */
+ if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
+ points /= 4;
+
+ dbg("task %d (%s) got %d points", p->pid, p->comm, points);
+ return points;
+}
+
+/*
+ * Simple selection loop. We chose the process with the highest
+ * number of 'points'. We expect the caller will lock the tasklist.
+ *
+ * (not docbooked, we don't want this one cluttering up the manual)
+ */
+static struct task_struct * select_bad_process(void)
+{
+ int maxpoints = 0;
+ struct task_struct *g, *p;
+ struct task_struct *chosen = NULL;
+
+ do_each_thread(g, p)
+ if (p->pid) {
+ int points = badness(p);
+ if (points > maxpoints) {
+ chosen = p;
+ maxpoints = points;
+ }
+ if (p->flags & PF_SWAPOFF)
+ return p;
+ }
+ while_each_thread(g, p);
+ return chosen;
+}
+
+/**
+ * We must be careful though to never send SIGKILL a process with
+ * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
+ * we select a process with CAP_SYS_RAW_IO set).
+ */
+static void __oom_kill_task(task_t *p)
+{
+ task_lock(p);
+ if (!p->mm || p->mm == &init_mm) {
+ WARN_ON(1);
+ warn("tried to kill an mm-less task!");
+ task_unlock(p);
+ return;
+ }
+ task_unlock(p);
+ error("Killed process %d (%s)", p->pid, p->comm);
+
+ /*
+ * We give our sacrificial lamb high priority and access to
+ * all the memory it needs. That way it should be able to
+ * exit() and clear out its resources quickly...
+ */
+ p->time_slice = HZ;
+ p->flags |= PF_MEMALLOC | PF_MEMDIE;
+
+ /* This process has hardware access, be more careful. */
+ if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO)) {
+ force_sig(SIGTERM, p);
+ } else {
+ force_sig(SIGKILL, p);
+ }
+}
+
+static struct mm_struct *oom_kill_task(task_t *p)
+{
+ struct parent_record *r;
+ struct mm_struct *mm = get_task_mm(p);
+ if (!mm || mm == &init_mm)
+ return NULL;
+
+ /*
+ * Hold parents accountable for their punk children :->
+ */
+ if (p->parent && p->parent->pid != 1) {
+ r = find_in_black_list(p->parent);
+ if (!r) {
+ dbg("Adding parent (%d) to black list because of %d",
+ p->parent->pid, p->pid);
+ black_list_parent(p);
+ } else {
+ if ( abs(jiffies - r->last_kill) >=
+ (oom_parent_expire*HZ) ) {
+ dbg("Removing parent (%d) from black list: "
+ "expired",
+ r->pid);
+ r->pid = 0;
+ } else if ( r->value >= oom_parent_max ) {
+ dbg("Marking parent (%d) for termination",
+ r->pid);
+ r->pid = 0;
+ p = r->task;
+ } else {
+ r->value++;
+ r->last_kill = jiffies;
+ dbg("Parent (%d) black list value increased "
+ "to %ld",
+ r->pid, r->value);
+ }
+ }
+ }
+
+ __oom_kill_task(p);
+ return mm;
+}
+
+
+/**
+ * oom_kill - kill the "best" process when we run out of memory
+ *
+ * If we run out of memory, we have the choice between either
+ * killing a random task (bad), letting the system crash (worse)
+ * OR try to be smart about which process to kill. Note that we
+ * don't have to be perfect here, we just have to be good.
+ */
+static void oom_kill(void)
+{
+ struct mm_struct *mm;
+ struct task_struct *g, *p, *q;
+
+ read_lock(&tasklist_lock);
+retry:
+ p = select_bad_process();
+
+ /* Found nothing?!?! Either we hang forever, or we panic. */
+ if (!p) {
+ show_free_areas();
+ panic("Out of memory and no killable processes...\n");
+ }
+
+ mm = oom_kill_task(p);
+ if (!mm)
+ goto retry;
+ /*
+ * kill all processes that share the ->mm (i.e. all threads),
+ * but are in a different thread group
+ */
+ do_each_thread(g, q)
+ if (q->mm == mm && q->tgid != p->tgid)
+ __oom_kill_task(q);
+ while_each_thread(g, q);
+ if (!p->mm)
+ printk(KERN_INFO "Fixed up OOM kill of mm-less task\n");
+ read_unlock(&tasklist_lock);
+ mmput(mm);
+
+ /*
+ * Make kswapd go out of the way, so "p" has a good chance of
+ * killing itself before someone else gets the chance to ask
+ * for more memory.
+ */
+ yield();
+ return;
+}
+
+/**
+ * out_of_memory - is the system out of memory?
+ */
+static void out_of_memory_killer(void)
+{
+ /*
+ * oom_lock protects out_of_memory()'s static variables.
+ * It's a global lock; this is not performance-critical.
+ */
+ static spinlock_t oom_lock = SPIN_LOCK_UNLOCKED;
+ static unsigned long first, last, count, lastkill;
+ unsigned long now, since;
+
+ /*
+ * Enough swap space left? Not OOM.
+ */
+ if (nr_swap_pages > 0)
+ return;
+
+ spin_lock(&oom_lock);
+ now = jiffies;
+ since = now - last;
+ last = now;
+
+ /*
+ * If it's been a long time since last failure,
+ * we're not oom.
+ */
+ last = now;
+ if (since > 5*HZ)
+ goto reset;
+
+ /*
+ * If we haven't tried for at least one second,
+ * we're not really oom.
+ */
+ since = now - first;
+ if (since < HZ)
+ goto out_unlock;
+
+ /*
+ * If we have gotten only a few failures,
+ * we're not really oom.
+ */
+ if (++count < 10)
+ goto out_unlock;
+
+ /*
+ * If we just killed a process, wait a while
+ * to give that task a chance to exit. This
+ * avoids killing multiple processes needlessly.
+ */
+ since = now - lastkill;
+ if (since < HZ*5)
+ goto out_unlock;
+
+ /*
+ * Ok, really out of memory. Kill something.
+ */
+ lastkill = now;
+
+ /* oom_kill() sleeps */
+ spin_unlock(&oom_lock);
+ oom_kill();
+ spin_lock(&oom_lock);
+
+reset:
+ /*
+ * We dropped the lock above, so check to be sure the variable
+ * first only ever increases to prevent false OOM's.
+ */
+ if (time_after(now, first))
+ first = now;
+ count = 0;
+
+out_unlock:
+ spin_unlock(&oom_lock);
+}
+
+static int oom_notify(struct notifier_block * s, unsigned long v, void * d)
+{
+ out_of_memory_killer();
+ return 0;
+}
+
+static struct notifier_block oom_nb = {
+ .notifier_call = oom_notify,
+};
+
+static int __init init_oom_kill(void)
+{
+ dbg("Registering oom_kill_parent handler");
+ return register_oom_notifier(&oom_nb);
+}
+module_init(init_oom_kill);
diff -Nru a/mm/oom_notifier.c b/mm/oom_notifier.c
--- /dev/null Wed Dec 31 16:00:00 1969
+++ b/mm/oom_notifier.c Fri Sep 12 18:59:35 2003
@@ -0,0 +1,38 @@
+/*
+ * linux/mm/oom_notifier.c
+ *
+ */
+
+#include <linux/init.h>
+#include <linux/vermagic.h>
+#include <linux/notifier.h>
+
+static DECLARE_MUTEX(notify_mutex);
+static struct notifier_block * oom_notify_list = 0;
+
+int register_oom_notifier(struct notifier_block * nb)
+{
+ int err;
+ down(&notify_mutex);
+ err = notifier_chain_register(&oom_notify_list, nb);
+ up(&notify_mutex);
+ return err;
+}
+EXPORT_SYMBOL(register_oom_notifier);
+
+int unregister_oom_notifier(struct notifier_block * nb)
+{
+ int err;
+ down(&notify_mutex);
+ err = notifier_chain_unregister(&oom_notify_list, nb);
+ up(&notify_mutex);
+ return err;
+}
+EXPORT_SYMBOL(unregister_oom_notifier);
+
+void out_of_memory(void)
+{
+ down(&notify_mutex);
+ notifier_call_chain(&oom_notify_list, OUT_OF_MEMORY, 0);
+ up(&notify_mutex);
+}
diff -Nru a/mm/oom_panic.c b/mm/oom_panic.c
--- /dev/null Wed Dec 31 16:00:00 1969
+++ b/mm/oom_panic.c Fri Sep 12 18:59:35 2003
@@ -0,0 +1,42 @@
+/*
+ * linux/mm/oom_panic.c
+ *
+ * This is a very simple component that will cause the kernel to
+ * panic on out-of-memory conditions. The behavior of panic can be
+ * further controlled with /proc/sys/kernel/panic.
+ *
+ * --rustyl <rusty@xxxxxxxxxxxxxxx>
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/notifier.h>
+#include <linux/oom_notifier.h>
+
+static int oom_notify(struct notifier_block * s, unsigned long v, void * d)
+{
+ panic("Out-Of-Memory");
+ return 0;
+}
+
+static struct notifier_block oom_nb = {
+ .notifier_call = oom_notify,
+};
+
+static int __init init_oom_panic(void)
+{
+ int err;
+ printk(KERN_INFO "Installing oom_panic handler\n");
+ err = register_oom_notifier(&oom_nb);
+ if (err) printk(KERN_ERR "Error installing oom_panic handler\n");
+ return err;
+}
+
+static void __exit exit_oom_panic(void)
+{
+ unregister_oom_notifier(&oom_nb);
+}
+
+module_init(init_oom_panic);
+module_exit(exit_oom_panic);
+MODULE_LICENSE("GPL");

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