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>

1 files changed, 25 insertions, 0 deletions

diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index 71f0fea1058f..56cee4727b1a 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/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