oom: deprecate oom_adj tunable

/proc/pid/oom_adj is now deprecated so that that it may eventually be
removed.  The target date for removal is August 2012.

A warning will be printed to the kernel log if a task attempts to use this
interface.  Future warning will be suppressed until the kernel is rebooted
to prevent spamming the kernel log.

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/feature-removal-schedule.txt

@@ -151,6 +151,31 @@ Who:	Eric Biederman <ebiederm@xmission.com>
 
 ---------------------------
 
+What:	/proc/<pid>/oom_adj
+When:	August 2012
+Why:	/proc/<pid>/oom_adj allows userspace to influence the oom killer's
+	badness heuristic used to determine which task to kill when the kernel
+	is out of memory.
+
+	The badness heuristic has since been rewritten since the introduction of
+	this tunable such that its meaning is deprecated.  The value was
+	implemented as a bitshift on a score generated by the badness()
+	function that did not have any precise units of measure.  With the
+	rewrite, the score is given as a proportion of available memory to the
+	task allocating pages, so using a bitshift which grows the score
+	exponentially is, thus, impossible to tune with fine granularity.
+
+	A much more powerful interface, /proc/<pid>/oom_score_adj, was
+	introduced with the oom killer rewrite that allows users to increase or
+	decrease the badness() score linearly.  This interface will replace
+	/proc/<pid>/oom_adj.
+
+	A warning will be emitted to the kernel log if an application uses this
+	deprecated interface.  After it is printed once, future warnings will be
+	suppressed until the kernel is rebooted.
+
+---------------------------
+
 What:	remove EXPORT_SYMBOL(kernel_thread)
 When:	August 2006
 Files:	arch/*/kernel/*_ksyms.c

Documentation/filesystems/proc.txt

@@ -1285,6 +1285,9 @@ scaled linearly with /proc/<pid>/oom_score_adj.
 Writing to /proc/<pid>/oom_score_adj or /proc/<pid>/oom_adj will change the
 other with its scaled value.
 
+NOTICE: /proc/<pid>/oom_adj is deprecated and will be removed, please see
+Documentation/feature-removal-schedule.txt.
+
 Caveat: when a parent task is selected, the oom killer will sacrifice any first
 generation children with seperate address spaces instead, if possible.  This
 avoids servers and important system daemons from being killed and loses the

fs/proc/base.c

@@ -1037,6 +1037,14 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
 		return -EACCES;
 	}
 
+	/*
+	 * Warn that /proc/pid/oom_adj is deprecated, see
+	 * Documentation/feature-removal-schedule.txt.
+	 */
+	printk_once(KERN_WARNING "%s (%d): /proc/%d/oom_adj is deprecated, "
+			"please use /proc/%d/oom_score_adj instead.\n",
+			current->comm, task_pid_nr(current),
+			task_pid_nr(task), task_pid_nr(task));
 	task->signal->oom_adj = oom_adjust;
 	/*
 	 * Scale /proc/pid/oom_score_adj appropriately ensuring that a maximum

include/linux/oom.h

@@ -2,6 +2,9 @@
 #define __INCLUDE_LINUX_OOM_H
 
 /*
+ * /proc/<pid>/oom_adj is deprecated, see
+ * Documentation/feature-removal-schedule.txt.
+ *
  * /proc/<pid>/oom_adj set to -17 protects from the oom-killer
  */
 #define OOM_DISABLE (-17)