+ oom_kill-oom_score_adj-broken-for-processes-with-small-memory-usage.patch added to -mm tree

+ oom_kill-oom_score_adj-broken-for-processes-with-small-memory-usage.patch added to -mm tree

[akpm]

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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Corey Minyard <cminyard@mvista.com>
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@acm.org
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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@mvista.com are

oom_kill-oom_score_adj-broken-for-processes-with-small-memory-usage.patch