mm: revert "oom: move oom_adj value"
The commit 2ff05b2b (oom: move oom_adj value) moveed the oom_adj value to
the mm_struct. It was a very good first step for sanitize OOM.
However Paul Menage reported the commit makes regression to his job
scheduler. Current OOM logic can kill OOM_DISABLED process.
Why? His program has the code of similar to the following.
...
set_oom_adj(OOM_DISABLE); /* The job scheduler never killed by oom */
...
if (vfork() == 0) {
set_oom_adj(0); /* Invoked child can be killed */
execve("foo-bar-cmd");
}
....
vfork() parent and child are shared the same mm_struct. then above
set_oom_adj(0) doesn't only change oom_adj for vfork() child, it's also
change oom_adj for vfork() parent. Then, vfork() parent (job scheduler)
lost OOM immune and it was killed.
Actually, fork-setting-exec idiom is very frequently used in userland program.
We must not break this assumption.
Then, this patch revert commit 2ff05b2b and related commit.
Reverted commit list
---------------------
- commit 2ff05b2b4e (oom: move oom_adj value from task_struct to mm_struct)
- commit 4d8b9135c3 (oom: avoid unnecessary mm locking and scanning for OOM_DISABLE)
- commit 8123681022 (oom: only oom kill exiting tasks with attached memory)
- commit 933b787b57 (mm: copy over oom_adj value at fork time)
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index fad18f9..ffead13 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -1167,13 +1167,11 @@
3.1 /proc/<pid>/oom_adj - Adjust the oom-killer score
------------------------------------------------------
-This file can be used to adjust the score used to select which processes should
-be killed in an out-of-memory situation. The oom_adj value is a characteristic
-of the task's mm, so all threads that share an mm with pid will have the same
-oom_adj value. A high value will increase the likelihood of this process being
-killed by the oom-killer. Valid values are in the range -16 to +15 as
-explained below and a special value of -17, which disables oom-killing
-altogether for threads sharing pid's mm.
+This file can be used to adjust the score used to select which processes
+should be killed in an out-of-memory situation. Giving it a high score will
+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
@@ -1187,9 +1185,6 @@
are the prime candidates to be killed. Having only one 'hungry' child will make
parent less preferable than the child.
-/proc/<pid>/oom_adj cannot be changed for kthreads since they are immune from
-oom-killing already.
-
/proc/<pid>/oom_score shows process' current badness score.
The following heuristics are then applied: