Commit 4d8b9135 authored by David Rientjes's avatar David Rientjes Committed by Linus Torvalds

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
...@@ -67,6 +67,10 @@ unsigned long badness(struct task_struct *p, unsigned long uptime) ...@@ -67,6 +67,10 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
return 0; return 0;
} }
oom_adj = mm->oom_adj; 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. * 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, ...@@ -253,15 +257,8 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
*ppoints = ULONG_MAX; *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); points = badness(p, uptime.tv_sec);
if (points > *ppoints || !chosen) { if (points > *ppoints) {
chosen = p; chosen = p;
*ppoints = points; *ppoints = points;
} }
...@@ -354,32 +351,13 @@ static int oom_kill_task(struct task_struct *p) ...@@ -354,32 +351,13 @@ static int oom_kill_task(struct task_struct *p)
struct mm_struct *mm; struct mm_struct *mm;
struct task_struct *g, *q; struct task_struct *g, *q;
task_lock(p);
mm = p->mm; mm = p->mm;
if (!mm || mm->oom_adj == OOM_DISABLE) {
/* WARNING: mm may not be dereferenced since we did not obtain its task_unlock(p);
* 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);
return 1; return 1;
} }
task_unlock(q); task_unlock(p);
} while_each_thread(g, q);
__oom_kill_task(p, 1); __oom_kill_task(p, 1);
/* /*
......
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