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Subject[take2] OOM documentation update [was: Linux killed Kenny, bastard!]
Updated version fixes some errors and extends description by adding
swapping and children relation explaintaion.


diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index d105eb4..4aa1918 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -2311,6 +2311,33 @@ increase the likelihood of this process being killed by the oom-killer. Valid
values are in the range -16 to +15, plus the special value -17, which disables
oom-killing altogether for this process.

+The process to be killed in an out-of-memory situation is selected among all others
+based on its badness score. This value equals the original memory size of the process
+originally and is then updated according to its CPU time (utime + stime) and the
+run time (uptime - start time). The longer it runs the smaller is the score.
+Badness score is divided by the square root of the cpu time and then by
+the double square root of the run time.
+Swapped out tasks are killed first. Half of each child's memory size is added to
+the parent's score if they do not share the same memory. Thus forking servers
+are the prime candidates to be killed. Having only one 'hungry' child will make
+parent less preferable than the child.
+/proc/<pid>/oom_score shows process' current badness score.
+The following heuristics are then applied:
+ * if the task was reniced, its score doubles
+ * superuser or direct hardware access tasks (CAP_SYS_ADMIN, CAP_SYS_RESOURCE
+ or CAP_SYS_RAWIO) have their score divided by 4
+ * if oom condition happened in one cpuset and checked task does not belong
+ to it, its score is divided by 8
+ * resulted score is multiplied by the two in the power of oom_adj when it is
+ positive, and divided otherwise, i.e.
+ points <<= oom_adj when it is positive and
+ points >>= oom_adj otherwise
+The task with the highest badness score is then killed.
2.13 /proc/<pid>/oom_score - Display current oom-killer score

Evgeniy Polyakov

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