proc_pid_oom_adj(5)

NAME#

/proc/pid/oom_score_adj - OOM-killer score adjustment

DESCRIPTION#

/proc/pid/oom_score_adj (since Linux 2.6.36)

This 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 (see cpuset(7)). 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 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 user space to control the preference for OOM-killing, ranging from always preferring a certain task or completely disabling it from OOM-killing. 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 user space to define the amount of memory to consider for each task. Setting an 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 backward compatibility with previous kernels, /proc/pid/oom_adj can still be used to tune the badness score. Its value is scaled linearly with oom_score_adj.

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

The choom(1) program provides a command-line interface for adjusting the oom_score_adj value of a running process or a newly executed command.

HISTORY#

/proc/pid/oom_adj (since Linux 2.6.11)

This file can be used to adjust the score used to select which process should be killed in an out-of-memory (OOM) situation. The kernel uses this value for a bit-shift operation of the process's oom_score value: valid values are in the range -16 to +15, plus the special value -17, which disables OOM-killing altogether for this process. A positive score increases the likelihood of this process being killed by the OOM-killer; a negative score decreases the likelihood.

The default value for this file is 0; a new process inherits its parent's oom_adj setting. A process must be privileged (CAP_SYS_RESOURCE) to update this file, although a process can always increase its own oom_adj setting (since Linux 2.6.20).

Since Linux 2.6.36, use of this file is deprecated in favor of /proc/pid/oom_score_adj, and finally removed in Linux 3.7.

SEE ALSO#

proc(5), proc_pid_oom_score(5)