oom: avoid unnecessary mm locking and scanning for OOM_DISABLE
This moves the check for OOM_DISABLE to the badness heuristic so it is
only necessary to hold task_lock() once. If the mm is OOM_DISABLE, the
score is 0, which is also correctly exported via /proc/pid/oom_score.
This requires that tasks with badness scores of 0 are prohibited from
being oom killed, which makes sense since they would not allow for future
memory freeing anyway.
Since the oom_adj value is a characteristic of an mm and not a task, it is
no longer necessary to check the oom_adj value for threads sharing the
same memory (except when simply issuing SIGKILLs for threads in other
thread groups).
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/mm/oom_kill.c b/mm/oom_kill.c
index b609135..cdcf89c 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -67,6 +67,10 @@
return 0;
}
oom_adj = mm->oom_adj;
+ if (oom_adj == OOM_DISABLE) {
+ task_unlock(p);
+ return 0;
+ }
/*
* The memory size of the process is the basis for the badness.
@@ -253,15 +257,8 @@
*ppoints = ULONG_MAX;
}
- task_lock(p);
- if (p->mm && p->mm->oom_adj == OOM_DISABLE) {
- task_unlock(p);
- continue;
- }
- task_unlock(p);
-
points = badness(p, uptime.tv_sec);
- if (points > *ppoints || !chosen) {
+ if (points > *ppoints) {
chosen = p;
*ppoints = points;
}
@@ -354,32 +351,13 @@
struct mm_struct *mm;
struct task_struct *g, *q;
+ task_lock(p);
mm = p->mm;
-
- /* WARNING: mm may not be dereferenced since we did not obtain its
- * value from get_task_mm(p). This is OK since all we need to do is
- * compare mm to q->mm below.
- *
- * Furthermore, even if mm contains a non-NULL value, p->mm may
- * change to NULL at any time since we do not hold task_lock(p).
- * However, this is of no concern to us.
- */
-
- if (mm == NULL)
+ if (!mm || mm->oom_adj == OOM_DISABLE) {
+ task_unlock(p);
return 1;
-
- /*
- * Don't kill the process if any threads are set to OOM_DISABLE
- */
- do_each_thread(g, q) {
- task_lock(q);
- if (q->mm == mm && q->mm && q->mm->oom_adj == OOM_DISABLE) {
- task_unlock(q);
- return 1;
- }
- task_unlock(q);
- } while_each_thread(g, q);
-
+ }
+ task_unlock(p);
__oom_kill_task(p, 1);
/*