oom: move oom_adj value from task_struct to mm_struct
The per-task oom_adj value is a characteristic of its mm more than the
task itself since it's not possible to oom kill any thread that shares the
mm. If a task were to be killed while attached to an mm that could not be
freed because another thread were set to OOM_DISABLE, it would have
needlessly been terminated since there is no potential for future memory
freeing.
This patch moves oomkilladj (now more appropriately named oom_adj) from
struct task_struct to struct mm_struct. This requires task_lock() on a
task to check its oom_adj value to protect against exec, but it's already
necessary to take the lock when dereferencing the mm to find the total VM
size for the badness heuristic.
This fixes a livelock if the oom killer chooses a task and another thread
sharing the same memory has an oom_adj value of OOM_DISABLE. This occurs
because oom_kill_task() repeatedly returns 1 and refuses to kill the
chosen task while select_bad_process() will repeatedly choose the same
task during the next retry.
Taking task_lock() in select_bad_process() to check for OOM_DISABLE and in
oom_kill_task() to check for threads sharing the same memory will be
removed in the next patch in this series where it will no longer be
necessary.
Writing to /proc/pid/oom_adj for a kthread will now return -EINVAL since
these threads are immune from oom killing already. They simply report an
oom_adj value of OOM_DISABLE.
Cc: Nick Piggin <npiggin@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: David Rientjes <rientjes@google.com>
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 cd8717a..ebff3c1 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -1003,11 +1003,13 @@
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. 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.
+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.
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
@@ -1021,6 +1023,9 @@
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: