Re: [PATCH 1/6] mm, oom: do not loop over all tasks if there are no external tasks sharing mm

[Tetsuo Handa]

Michal Hocko wrote:
> On Fri 27-05-16 00:25:23, Tetsuo Handa wrote:
> > I think that remembering whether this mm might be shared between
> > multiple thread groups at clone() time (i.e. whether
> > clone(CLONE_VM without CLONE_SIGHAND) was ever requested on this mm)
> > is safe (given that that thread already got SIGKILL or is exiting).
> 
> I was already playing with that idea but I didn't want to add anything
> to the fork path which is really hot. This patch is not really needed
> for the rest. It just felt like a nice optimization. I do not think it
> is worth deeper changes in the fast paths.

"[PATCH 6/6] mm, oom: fortify task_will_free_mem" depends on [PATCH 1/6].
You will need to update [PATCH 6/6].

It seems to me that [PATCH 6/6] resembles
http://lkml.kernel.org/r/201605250005.GHH26082.JOtQOSLMFFOFVH@xxxxxxxxxxxxxxxxxxx .
I think we will be happy if we can speed up mm_is_reapable() test using
"whether this mm might be shared between multiple thread groups" flag.
I don't think updating such flag at clone() is too heavy operation to add.