[RFC] Enabling other oom schemes

From: Rusty Lynch
Date: Thu Sep 11 2003 - 21:21:13 EST

Over the years I have encountered various usage needs where the standard
oom_kill.c version of memory recovery was not the most ideal approach.
For example, some times it is better to just restart the system and
let a front end load balancer hand off the server load to another system.
Sometimes it might be worth the effort to write a very solution specific
oom handler.

Every now and then I hear rumblings of changing the way oom is handled by
using modules, or something. Since I was not able to uncover any actual
proposals, here is my quick attempt.

The patch below uses a notifier list for other components to register
to be called when an out of memory condition occurs. Basically:

* Added include/linux/oom_notifier.h and mm/oom_notifier.c
which add (un)registration functions and also provide the
out_of_memory() entry function that use to be held in mm/oom_kill.c

* Tweaked mm/oom_kill.c so that it can be enabled at build time.
(I wasn't able to make it build as a module because it is using
a few non-exported symbols in linux/mm/*)

* 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.

--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 1.1284 -> 1.1285
# include/linux/notifier.h 1.4 -> 1.5
# mm/oom_kill.c 1.24 -> 1.25
# mm/Makefile 1.24 -> 1.25
# init/Kconfig 1.28 -> 1.29
# (new) -> 1.1 mm/oom_panic.c
# (new) -> 1.1 include/linux/oom_notifier.h
# (new) -> 1.1 mm/oom_notifier.c
#
# The following is the BitKeeper ChangeSet Log
# --------------------------------------------
# 03/09/11 rusty@xxxxxxxxxxxxxxxxxxxx 1.1285
# Initial attempt at an oom notifier
# --------------------------------------------
#
diff -Nru a/include/linux/notifier.h b/include/linux/notifier.h
--- a/include/linux/notifier.h Thu Sep 11 18:34:47 2003
+++ b/include/linux/notifier.h Thu Sep 11 18:34:47 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 Thu Sep 11 18:34:47 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/init/Kconfig b/init/Kconfig
--- a/init/Kconfig Thu Sep 11 18:34:47 2003
+++ b/init/Kconfig Thu Sep 11 18:34:47 2003
@@ -162,6 +162,21 @@
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.

menuconfig EMBEDDED
bool "Remove kernel features (for embedded systems)"
diff -Nru a/mm/Makefile b/mm/Makefile
--- a/mm/Makefile Thu Sep 11 18:34:47 2003
+++ b/mm/Makefile Thu Sep 11 18:34:47 2003
@@ -7,8 +7,11 @@
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
diff -Nru a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c Thu Sep 11 18:34:47 2003
+++ b/mm/oom_kill.c Thu Sep 11 18:34:47 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_notifier.c b/mm/oom_notifier.c
--- /dev/null Wed Dec 31 16:00:00 1969
+++ b/mm/oom_notifier.c Thu Sep 11 18:34:47 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 Thu Sep 11 18:34:47 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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