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 set-
       ting.

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 al-
       lowed 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 cur-
       rent 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 allocat-
       ing 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  mem-
       policy  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 dis-
       abling it.  The lowest possible value, -1000,  is  equivalent  to  dis-
       abling 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  equiva-
       lent  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)