path: root/Documentation
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authorEvgeniy Polyakov <zbr@ioremap.net>2009-01-29 14:25:09 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2009-01-29 18:04:43 -0800
commit9e9e3cbc62da43c66e894d5a61fa08b427e25202 (patch)
tree5dafdeb919c99a014e694745c2dfe4c46ca6f69e /Documentation
parentdc19835df6c47ff676ad6c98722d5e529db5d74c (diff)
mm: OOM documentation update
Signed-off-by: Evgeniy Polyakov <zbr@ioremap.net> Acked-by: David Rientjes <rientjes@google.com> Cc: Randy Dunlap <randy.dunlap@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
1 files changed, 28 insertions, 0 deletions
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index bbebc3a43ac..a87be42f821 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -2027,6 +2027,34 @@ increase the likelihood of this process being killed by the oom-killer. Valid
values are in the range -16 to +15, plus the special value -17, which disables
oom-killing altogether for this process.
+The process to be killed in an out-of-memory situation is selected among all others
+based on its badness score. This value equals the original memory size of the process
+and is then updated according to its CPU time (utime + stime) and the
+run time (uptime - start time). The longer it runs the smaller is the score.
+Badness score is divided by the square root of the CPU time and then by
+the double square root of the run time.
+Swapped out tasks are killed first. Half of each child's memory size is added to
+the parent's score if they do not share the same memory. Thus forking servers
+are the prime candidates to be killed. Having only one 'hungry' child will make
+parent less preferable than the child.
+/proc/<pid>/oom_score shows process' current badness score.
+The following heuristics are then applied:
+ * if the task was reniced, its score doubles
+ * superuser or direct hardware access tasks (CAP_SYS_ADMIN, CAP_SYS_RESOURCE
+ or CAP_SYS_RAWIO) have their score divided by 4
+ * if oom condition happened in one cpuset and checked task does not belong
+ to it, its score is divided by 8
+ * the resulting score is multiplied by two to the power of oom_adj, i.e.
+ points <<= oom_adj when it is positive and
+ points >>= -(oom_adj) otherwise
+The task with the highest badness score is then selected and its children
+are killed, process itself will be killed in an OOM situation when it does
+not have children or some of them disabled oom like described above.
2.13 /proc/<pid>/oom_score - Display current oom-killer score