/proc/<pid>/oom_score displays the current oom-killer score. This file can be used to check the current score used by the oom-killer is for any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which process should be killed in an out-of-memory situation.

/proc/<pid>/oom_adj and /proc/<pid>/oom_score_adj adjust the oom-killer score.

These file can be used to adjust the badness heuristic used to select which process gets killed in out of memory conditions.

The badness heuristic assigns a value to each candidate task ranging from 0 (never kill) to 1000 (always kill) to determine which process is targeted. The units are roughly a proportion along that range of allowed memory the process may allocate from based on an estimation of its current memory and swap use. For example, if a task is using all allowed memory, its badness score will be 1000. If it is using half of its allowed memory, its score will be 500.

There is an additional factor included in the badness score: root processes are given 3% extra memory over other tasks.

The amount of “allowed” memory depends on the context in which the oom killer was called. If it is due to the memory assigned to the allocating task's cpuset being exhausted, the allowed memory represents the set of mems assigned to that cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed memory represents the set of mempolicy nodes. If it is due to a memory limit (or swap limit) being reached, the allowed memory is that configured limit. Finally, if it is due to the entire system being out of memory, the allowed memory represents all allocatable resources.

The value of /proc/<pid>/oom_score_adj is added to the badness score before it is used to determine which task to kill. Acceptable values range from -1000 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to polarize the preference for oom killing either by always preferring a certain task or completely disabling it. The lowest possible value, -1000, is equivalent to disabling oom killing entirely for that task since it will always report a badness score of 0.

Consequently, it is very simple for userspace to define the amount of memory to consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for example, is roughly equivalent to allowing the remainder of tasks sharing the same system, cpuset, mempolicy, or memory controller resources to use at least 50% more memory. A value of -500, on the other hand, would be roughly equivalent to discounting 50% of the task's allowed memory from being considered as scoring against the task.

For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also be used to tune the badness score. Its acceptable values range from -16 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17 (OOM_DISABLE) to disable oom killing entirely for that task. Its value is scaled linearly with /proc/<pid>/oom_score_adj.

Writing to /proc/<pid>/oom_score_adj or /proc/<pid>/oom_adj will change the other with its scaled value.