linux-kernel - [patch] oom: document obsolete oom

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Message-ID: <alpine.DEB.2.00.1011091555210.30112@chino.kir.corp.google.com>
Date:	Tue, 9 Nov 2010 15:55:53 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
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@...rguk.ukuu.org.uk>
Signed-off-by: David Rientjes <rientjes@...gle.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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