Re: [PATCH] mm,oom: use per signal_struct flag rather than clear TIF_MEMDIE

[Michal Hocko <mhocko@kernel.org>]

On Wed 29-06-16 22:14:09, Oleg Nesterov wrote:
> On 06/28, Michal Hocko wrote:
> >
> > On Mon 27-06-16 19:55:55, Oleg Nesterov wrote:
> > > On 06/27, Michal Hocko wrote:
> > > >
> > > > On Mon 27-06-16 17:51:20, Oleg Nesterov wrote:
> > > > >
> > > > > Yes I agree, it would be nice to remove find_lock_task_mm(). And in
> > > > > fact it would be nice to kill task_struct->mm (but this needs a lot
> > > > > of cleanups). We probably want signal_struct->mm, but this is a bit
> > > > > complicated (locking).
> > > >
> > > > Is there any hard requirement to reset task_struct::mm in the first
> > > > place?
> > >
> > > Well, at least the scheduler needs this.
> >
> > Could you point me to where it depends on that? I mean if we are past
> > exit_mm then we have unmapped the address space most probably but why
> > should we care about that in the scheduler? There shouldn't be any
> > further access to the address space by that point. I can see that
> > context_switch() checks task->mm but it should just work when it sees it
> > non NULL, right?
> 
> But who will do the final mmdrop() then? I am not saying this is impossible
> to change, say we do this in finish_task_switch(TASK_DEAD) or even in
> free_task(), but we do not want this?

I thought it could be done somewhere in release_task after we unhash
the process but then we would need something for the exlusion (possibly
task_lock) to handle races when the oom killer sees a task while it is
being unhashed. I guess it should be doable...
-- 
Michal Hocko
SUSE Labs

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