1CHOOM(1) User Commands CHOOM(1)
2
6 choom - display and adjust OOM-killer score.
7
9 choom -p pid
10 choom -p pid -n number
12 choom -n number command [argument...]
14
17 The choom command displays and adjusts Out-Of-Memory killer score set‐
18 ting.
19
22 -p, --pid pid
23 Specifies process ID.
24 -n, --adjust value
26 Specify the adjust score value.
27 -h, --help
29 Display help text and exit.
30 -V, --version
32 Display version information and exit.
33
35 Linux kernel uses the badness heuristic to select which process gets
36 killed in out of memory conditions.
37 The badness heuristic assigns a value to each candidate task ranging
39 from 0 (never kill) to 1000 (always kill) to determine which process is
40 targeted. The units are roughly a proportion along that range of
41 allowed memory the process may allocate from based on an estimation of
42 its current memory and swap use. For example, if a task is using all
43 allowed memory, its badness score will be 1000. If it is using half of
44 its allowed memory, its score will be 500.
45 There is an additional factor included in the badness score: the cur‐
47 rent memory and swap usage is discounted by 3% for root processes.
48 The amount of "allowed" memory depends on the context in which the oom
50 killer was called. If it is due to the memory assigned to the allocat‐
51 ing task's cpuset being exhausted, the allowed memory represents the
52 set of mems assigned to that cpuset. If it is due to a mempolicy's
53 node(s) being exhausted, the allowed memory represents the set of mem‐
54 policy nodes. If it is due to a memory limit (or swap limit) being
55 reached, the allowed memory is that configured limit. Finally, if it
56 is due to the entire system being out of memory, the allowed memory
57 represents all allocatable resources.
58 The adjust score value is added to the badness score before it is used
60 to determine which task to kill. Acceptable values range from -1000 to
61 +1000. This allows userspace to polarize the preference for oom
62 killing either by always preferring a certain task or completely dis‐
63 abling it. The lowest possible value, -1000, is equivalent to dis‐
64 abling oom killing entirely for that task since it will always report a
65 badness score of 0.
66 Setting an adjust score value of +500, for example, is roughly equiva‐
68 lent to allowing the remainder of tasks sharing the same system,
69 cpuset, mempolicy, or memory controller resources to use at least 50%
70 more memory. A value of -500, on the other hand, would be roughly
71 equivalent to discounting 50% of the task's allowed memory from being
72 considered as scoring against the task.
73
76 Karel Zak <kzak@redhat.com>
77
79 proc(5)
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82 The choom command is part of the util-linux package and is available
83 from Linux Kernel Archive ⟨https://www.kernel.org/pub/linux/utils/util-
84 linux/⟩.
85util-linux April 2018 CHOOM(1)