Re: [PATCH 10/10] mm, oom: hide mm which is shared with kthread or global init

[Andrew Morton]

On Tue, 19 Jul 2016 14:05:39 +0200 Michal Hocko <mhocko@xxxxxxxxxx> wrote:

> > After this patch we should guarantee a forward progress for the OOM
> > killer even when the selected victim is sharing memory with a kernel
> > thread or global init.
> 
> Could you replace the last two paragraphs with the following. Tetsuo
> didn't like the guarantee mentioned there because that is a too strong
> statement as find_lock_task_mm might not find any mm and so we still
> could end up looping on the oom victim if it gets stuck somewhere in
> __mmput. This particular patch didn't aim at closing that case. Plugging
> that hole is planned later after the next upcoming merge window closes.
> 
> "
> In order to help a forward progress for the OOM killer, make sure
> that this really rare cases will not get into the way and hide
> the mm from the oom killer by setting MMF_OOM_REAPED flag for it.
> oom_scan_process_thread will ignore any TIF_MEMDIE task if it has
> MMF_OOM_REAPED flag set to catch these oom victims.
> 		        
> After this patch we should guarantee a forward progress for the OOM
> killer even when the selected victim is sharing memory with a kernel
> thread or global init as long as the victims mm is still alive.
> "

I tweaked it a bit:

: In order to help forward progress for the OOM killer, make sure that
: this really rare case will not get in the way - we do this by hiding
: the mm from the oom killer by setting MMF_OOM_REAPED flag for it. 
: oom_scan_process_thread will ignore any TIF_MEMDIE task if it has
: MMF_OOM_REAPED flag set to catch these oom victims.
: 
: After this patch we should guarantee forward progress for the OOM
: killer even when the selected victim is sharing memory with a kernel
: thread or global init as long as the victims mm is still alive.