From 4d8b9135c30ccbe46e621fefd862969819003fd6 Mon Sep 17 00:00:00 2001 From: David Rientjes Date: Tue, 16 Jun 2009 15:32:57 -0700 Subject: [PATCH] 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 Cc: Rik van Riel Cc: Mel Gorman Signed-off-by: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/oom_kill.c | 42 ++++++++++-------------------------------- 1 file changed, 10 insertions(+), 32 deletions(-) diff --git a/mm/oom_kill.c b/mm/oom_kill.c index b60913520ef3..cdcf89cb9ff2 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -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) + 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); /*