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Commit 4d8b9135 authored by David Rientjes's avatar David Rientjes Committed by Linus Torvalds
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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: default avatarDavid Rientjes <rientjes@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2ff05b2b

mm/oom_kill.c

+10 −32
Original line number Diff line number Diff line
@@ -67,6 +67,10 @@ unsigned long badness(struct task_struct *p, unsigned long uptime) 
		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 @@ static struct task_struct *select_bad_process(unsigned long *ppoints, 
			*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 @@ static int oom_kill_task(struct task_struct *p) 
	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)

		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);

	if (!mm || mm->oom_adj == OOM_DISABLE) {

		task_unlock(p);

		return 1;

	}

		task_unlock(q);

	} while_each_thread(g, q);



	task_unlock(p);

	__oom_kill_task(p, 1);



	/*