mm: OOM documentation update
Signed-off-by: Evgeniy Polyakov <zbr@ioremap.net> Acked-by: David Rientjes <rientjes@google.com> Cc: Randy Dunlap <randy.dunlap@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -2027,6 +2027,34 @@ increase the likelihood of this process being killed by the oom-killer. Valid
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values are in the range -16 to +15, plus the special value -17, which disables
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oom-killing altogether for this process.
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The process to be killed in an out-of-memory situation is selected among all others
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based on its badness score. This value equals the original memory size of the process
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and is then updated according to its CPU time (utime + stime) and the
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run time (uptime - start time). The longer it runs the smaller is the score.
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Badness score is divided by the square root of the CPU time and then by
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the double square root of the run time.
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Swapped out tasks are killed first. Half of each child's memory size is added to
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the parent's score if they do not share the same memory. Thus forking servers
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are the prime candidates to be killed. Having only one 'hungry' child will make
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parent less preferable than the child.
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/proc/<pid>/oom_score shows process' current badness score.
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The following heuristics are then applied:
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* if the task was reniced, its score doubles
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* superuser or direct hardware access tasks (CAP_SYS_ADMIN, CAP_SYS_RESOURCE
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or CAP_SYS_RAWIO) have their score divided by 4
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* if oom condition happened in one cpuset and checked task does not belong
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to it, its score is divided by 8
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* the resulting score is multiplied by two to the power of oom_adj, i.e.
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points <<= oom_adj when it is positive and
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points >>= -(oom_adj) otherwise
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The task with the highest badness score is then selected and its children
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are killed, process itself will be killed in an OOM situation when it does
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not have children or some of them disabled oom like described above.
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2.13 /proc/<pid>/oom_score - Display current oom-killer score
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-------------------------------------------------------------
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