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What: /proc/<pid>/oom_adj
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When: August 2012
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Why: /proc/<pid>/oom_adj allows userspace to influence the oom killer's
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badness heuristic used to determine which task to kill when the kernel
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is out of memory.
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The badness heuristic has since been rewritten since the introduction of
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this tunable such that its meaning is deprecated. The value was
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implemented as a bitshift on a score generated by the badness()
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function that did not have any precise units of measure. With the
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rewrite, the score is given as a proportion of available memory to the
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task allocating pages, so using a bitshift which grows the score
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exponentially is, thus, impossible to tune with fine granularity.
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A much more powerful interface, /proc/<pid>/oom_score_adj, was
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introduced with the oom killer rewrite that allows users to increase or
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decrease the badness score linearly. This interface will replace
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/proc/<pid>/oom_adj.
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A warning will be emitted to the kernel log if an application uses this
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deprecated interface. After it is printed once, future warnings will be
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suppressed until the kernel is rebooted.
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