choom

CHOOM(1)                         User Commands                        CHOOM(1)



NAME
       choom - display and adjust OOM-killer score.

SYNOPSIS
       choom -p pid

       choom -p pid -n number

       choom -n number command [argument...]


DESCRIPTION
       The choom command displays and adjusts Out-Of-Memory killer score
       setting.


OPTIONS
       -p, --pid pid
              Specifies process ID.

       -n, --adjust value
              Specify the adjust score value.

       -h, --help
              Display help text and exit.

       -V, --version
              Display version information and exit.

NOTES
       Linux kernel uses the badness heuristic 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: the
       current memory and swap usage is discounted by 3% for root processes.

       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 adjust score value is added to the badness score before it is used
       to determine which task to kill.  Acceptable values range from -1000 to
       +1000.  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.

       Setting an adjust score 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.


AUTHORS
       Karel Zak <kzak@redhat.com>

SEE ALSO
       proc(5)

AVAILABILITY
       The choom command is part of the util-linux package and is available
       from Linux Kernel Archive ⟨https://www.kernel.org/pub/linux/utils/util-
       linux/⟩.



util-linux                        April 2018                          CHOOM(1)