Messages in this thread | | | Date | Wed, 14 Jan 2009 16:58:41 -0800 (PST) | From | David Rientjes <> | Subject | Re: [take3] OOM documentation update [was: Linux killed Kenny, bastard!] |
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On Thu, 15 Jan 2009, Evgeniy Polyakov wrote:
> diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt > index d105eb4..eed2fbb 100644 > --- a/Documentation/filesystems/proc.txt > +++ b/Documentation/filesystems/proc.txt > @@ -2311,6 +2311,32 @@ 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 > +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 > + * the resulting score is multiplied by two to the power of oom_adj, i.e. > + points <<= oom_adj when it is positive and > + points >>= -(oom_adj) otherwise > + > +The task with the highest badness score is then killed. > +
Not quite, even after a task is selected for oom kill, the oom killer still prefers to kill one of its children first if any have a different mm. See oom_kill_process().
You also don't mention the exception of OOM_DISABLE (oom_adj score of -17) in your formula for how oom_adj impacts the points value. Although its already explained earlier, it should be mentioned here since a oom_adj is an int and a right shift of 17 does not guarantee `points' will be 0.
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