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On Mon, 1 Feb 2010, KAMEZAWA Hiroyuki wrote:

> > > 109 /*
> > > 110 * Processes which fork a lot of child processes are likely
> > > 111 * a good choice. We add half the vmsize of the children if they
> > > 112 * have an own mm. This prevents forking servers to flood the
> > > 113 * machine with an endless amount of children. In case a single
> > > 114 * child is eating the vast majority of memory, adding only half
> > > 115 * to the parents will make the child our kill candidate of
> > > choice.
> > > 116 */
> > > 117 list_for_each_entry(child, &p->children, sibling) {
> > > 118 task_lock(child);
> > > 119 if (child->mm != mm && child->mm)
> > > 120 points += child->mm->total_vm/2 + 1;
> > > 121 task_unlock(child);
> > > 122 }
> > > 123
> > > ==
> > > This makes task launcher(the fist child of some daemon.) first victim.
> >
> > That "victim", p, is passed to oom_kill_process() which does this:
> >
> > /* Try to kill a child first */
> > list_for_each_entry(c, &p->children, sibling) {
> > if (c->mm == p->mm)
> > continue;
> > if (!oom_kill_task(c))
> > return 0;
> > }
> > return oom_kill_task(p);
> >
>
> Then, finally, per-process oom_adj(!=OOM_DISABLE) control is ignored ?
> Seems broken.
>

No, oom_kill_task() returns 1 if the child has OOM_DISABLE set, meaning it
never gets killed and we continue iterating through the child list. If
there are no children with seperate memory to kill, the selected task gets
killed. This prevents things from like sshd or bash from getting killed
unless they are actually the memory leaker themselves.

It would naturally be better to select the child with the highest
badness() score, but it only depends on the ordering of p->children at the
moment. That's because we only want to iterate through this potentially
long list once, but improvements in this area (as well as sane tweaks to
the heuristic) would certainly be welcome.


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