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Subject[patch] oom: document obsolete oom_adj tunable
/proc/pid/oom_adj was deprecated in August 2010 with the introduction of
the new oom killer heuristic.

This patch copies the Documentation/feature-removal-schedule.txt entry
for this tunable to the Documentation/ABI/obsolete directory so nobody
misses it.

Reported-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: David Rientjes <rientjes@google.com>
---
Documentation/ABI/obsolete/proc-pid-oom_adj | 22 ++++++++++++++++++++++
1 files changed, 22 insertions(+), 0 deletions(-)
create mode 100644 Documentation/ABI/obsolete/proc-pid-oom_adj

diff --git a/Documentation/ABI/obsolete/proc-pid-oom_adj b/Documentation/ABI/obsolete/proc-pid-oom_adj
new file mode 100644
--- /dev/null
+++ b/Documentation/ABI/obsolete/proc-pid-oom_adj
@@ -0,0 +1,22 @@
+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.

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