Re: [PATCH 4/6] mm, oom: skip vforked tasks from being selected

On Thu 02-06-16 20:31:57, Tetsuo Handa wrote:

Michal Hocko wrote:

quoted

OK, but the memory is allocated on behalf of the parent already, right?

What does "the memory is allocated on behalf of the parent already" mean?

It means that vforked task cannot allocate a new memory directly. Sure
it can get a copy of what parent already has allocated during execve but
that is under control of the parent. If the parent is OOM_SCORE_ADJ_MIN
then it should better be careful how it spawns new tasks.

The memory used for argv[]/envp[] may not yet be visible from mm_struct when
the OOM killer is invoked.

quoted

And the patch doesn't prevent parent from being selected and the vfroked
child being killed along the way as sharing the mm with it. So what
exactly this patch changes for this test case? What am I missing?

If the parent is OOM_SCORE_ADJ_MIN and vfork()ed child doing execve()
with large argv[]/envp[] is not OOM_SCORE_ADJ_MIN, we should not hesitate
to OOM-kill vfork()ed child even if the parent is not OOM-killable.

	vfork()
	set_oom_adj()
	exec()

Well the whole point of this patch is to not select such a task because
it makes only very limitted sense. It cannot really free much memory -
well except when parent is doing something realy stupid which I am not
really sure we should care about.
-- 
Michal Hocko
SUSE Labs

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