Re: [RFC PATCH] PM: Optionally block user fork during freeze to improve performance

[Michal Hocko]

On Mon 16-06-25 09:45:59, David Hildenbrand wrote:
> 
> > > [...]
> > In our test scenario, although new processes can indeed be created
> > during the usleep_range() intervals between freeze iterations, it’s
> > actually difficult to make the freezer fail outright. This is because
> > user processes are forcibly frozen: when they return to user space and
> > check for pending signals, they enter try_to_freeze() and transition
> > into the refrigerator.
> > 
> > However, since the scheduler is fair by design, it gives both newly
> > forked tasks and yet-to-be-frozen tasks a chance to run. This
> > competition for CPU time can slightly delay the overall freeze process.
> > While this typically doesn’t lead to failure, it does cause more retries
> > than necessary, especially under CPU pressure.
> 
> I think that goes back to my original comment: why are we even allowing fork
> children to run at all when we are currently freezing all tasks?

The same should be the case for cgroup freezer as well.
-- 
Michal Hocko
SUSE Labs