Re: [PATCH] OOM killer API (was: [PATCH] VM fix for 2.4.0-test9 & OOM handler)

[Ingo Oeser <ingo.oeser@informatik.tu-chemnitz.de>]

On Tue, Oct 10, 2000 at 12:32:50PM -0300, Rik van Riel wrote:
> > So now you can stop arguing about the one and only OOM killer,
> > implement it, provide it as module and get back to the important
> > stuff ;-)
> 
> This is definately a cool toy for people who have doubts
> that my OOM killer will do the wrong thing in their
> workloads.

Thanks ;-)

But I forgot to include my changes to the mm/Makefile (to export
the API for modules).

Here is a _working_ one:

--- linux-2.4.0-test10-pre1/mm/oom_kill.c	Tue Oct 10 16:31:08 2000
+++ linux-2.4.0-test10-pre1-ioe/mm/oom_kill.c	Tue Oct 10 16:59:27 2000
@@ -13,6 +13,8 @@
  *  machine) this file will double as a 'coding guide' and a signpost
  *  for newbie kernel hackers. It features several pointers to major
  *  kernel subsystems and hints as to where to find out what things do.
+ *
+ *  Added oom_killer API for special needs - Ingo Oeser
  */
 
 #include <linux/mm.h>
@@ -136,7 +138,7 @@
 }
 
 /**
- * oom_kill - kill the "best" process when we run out of memory
+ * oom_kill_rik - 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)
@@ -147,7 +149,9 @@
  * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
  * we select a process with CAP_SYS_RAW_IO set).
  */
-void oom_kill(void)
+
+
+static void oom_kill_rik(void)
 {
 
 	struct task_struct *p = select_bad_process();
@@ -207,4 +211,63 @@
 
 	/* Else... */
 	return 1;
+}
+
+/* Protects oom_killer against resetting during its execution */
+static rwlock_t oom_kill_lock = RW_LOCK_UNLOCKED;
+
+static oom_killer_t oom_killer = oom_kill_rik;
+
+/** 
+ * oom_kill - the oom_kill wrapper for installable OOM killers
+ *
+ * Wraper around the OOM killers, that can be installed via
+ * install_oom_killer and reset_default_oom_killer.
+ *
+ * This gets called from kswapd() in linux/mm/vmscan.c when we 
+ * really run out of memory.
+ */
+void oom_kill(void) {
+	read_lock(&oom_kill_lock);
+	oom_killer();
+	read_unlock(&oom_kill_lock);
+}
+
+/**
+ * install_oom_killer - install alternate OOM killer
+ * @new_oom_kill: the alternate OOM killer provided by the caller
+ *
+ * Since the default OOM killer (oom_kill_rik) is not suitable 
+ * for everyone, we provide an interface to install custom OOM killers.
+ * 
+ * You can take the most appropriate action for your application if the
+ * kernel goes OOM.
+ *
+ * Providing an NULL argument just returns the current OOM killer.
+ *
+ * Returns: The OOM killer, which has been installed so far.
+ * 
+ * NOTE: We don't do refcounting on OOM killers, so be careful with 
+ * 	modules
+ */
+oom_killer_t install_oom_killer(oom_killer_t new_oom_kill) {
+	oom_killer_t tmp;
+	write_lock(&oom_kill_lock);
+	tmp=oom_killer;
+	if (new_oom_kill) 
+		oom_killer=new_oom_kill;
+	write_unlock(&oom_kill_lock);
+	return tmp;
+}
+
+/**
+ * reset_default_oom_killer - reset back to default OOM killer
+ *
+ * If you are going to unload the module which provided 
+ * your OOM killer, you can install the default one by this.
+ *
+ * Returns: The OOM killer, which has been installed so far.
+ */
+oom_killer_t reset_default_oom_killer(void) {
+	return install_oom_killer(&oom_kill_rik);
 }
--- linux-2.4.0-test10-pre1/include/linux/swap.h	Tue Oct 10 16:31:08 2000
+++ linux-2.4.0-test10-pre1-ioe/include/linux/swap.h	Tue Oct 10 16:44:22 2000
@@ -127,8 +127,14 @@
 #define read_swap_cache(entry) read_swap_cache_async(entry, 1);
 
 /* linux/mm/oom_kill.c */
+typedef void (*oom_killer_t)(void);
+
 extern int out_of_memory(void);
 extern void oom_kill(void);
+
+oom_killer_t install_oom_killer(oom_killer_t new_oom_kill);
+oom_killer_t reset_default_oom_killer(void);
+
 
 /*
  * Make these inline later once they are working properly.
--- linux-2.4.0-test10-pre1/mm/Makefile	Tue Oct 10 16:31:08 2000
+++ linux-2.4.0-test10-pre1-ioe/mm/Makefile	Tue Oct 10 16:34:06 2000
@@ -10,7 +10,8 @@
 O_TARGET := mm.o
 O_OBJS	 := memory.o mmap.o filemap.o mprotect.o mlock.o mremap.o \
 	    vmalloc.o slab.o bootmem.o swap.o vmscan.o page_io.o \
-	    page_alloc.o swap_state.o swapfile.o numa.o oom_kill.o
+	    page_alloc.o swap_state.o swapfile.o numa.o
+OX_OBJS  := oom_kill.o
 
 ifeq ($(CONFIG_HIGHMEM),y)
 O_OBJS += highmem.o

Regards

Ingo Oeser
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