The patch titled
Subject: oom_kill: oom_score_adj broken for processes with small memory usage
has been added to the -mm tree. Its filename is
oom_kill-oom_score_adj-broken-for-processes-with-small-memory-usage.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/oom_kill-oom_score_adj-broken-for-processes-with-small-memory-usage.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/oom_kill-oom_score_adj-broken-for-processes-with-small-memory-usage.patch
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------------------------------------------------------
From: Corey Minyard <cminyard@xxxxxxxxxx>
Subject: oom_kill: oom_score_adj broken for processes with small memory usage
If you have a process with less than 1000 totalpages, the calculation:
adj = (long)p->signal->oom_score_adj;
...
adj *= totalpages / 1000;
will always result in adj being zero no matter what oom_score_adj is,
which could result in the wrong process being picked for killing.
Fix by adding 1000 to totalpages before dividing.
I ran across this trying to diagnose another problem where I set up a
cgroup with a small amount of memory and couldn't get a test program to
work right.
I'm not sure this is quite right, to keep closer to the current behavior
you could do:
if (totalpages >= 1000) adj *= totalpages / 1000;
but that would map 0-1999 to the same value. But this at least shows the
issue. I can provide a test program the shows the issue, but I think it's
pretty obvious from the code.
Link: https://lkml.kernel.org/r/20210701125430.836308-1-minyard@xxxxxxx
Signed-off-by: Corey Minyard <cminyard@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/oom_kill.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
--- a/mm/oom_kill.c~oom_kill-oom_score_adj-broken-for-processes-with-small-memory-usage
+++ a/mm/oom_kill.c
@@ -233,8 +233,11 @@ long oom_badness(struct task_struct *p,
mm_pgtables_bytes(p->mm) / PAGE_SIZE;
task_unlock(p);
- /* Normalize to oom_score_adj units */
- adj *= totalpages / 1000;
+ /*
+ * Normalize to oom_score_adj units. You should never
+ * multiply by zero here, or oom_score_adj will not work.
+ */
+ adj *= (totalpages + 1000) / 1000;
points += adj;
return points;
_
Patches currently in -mm which might be from cminyard@xxxxxxxxxx are
oom_kill-oom_score_adj-broken-for-processes-with-small-memory-usage.patch
