Re: [PATCH v1 02/25] mm/swap: Don't abuse the seqcount latching API

Peter Zijlstra
2020-05-25T15:45:31Z

On Mon, May 25, 2020 at 05:24:01PM +0200, Ahmed S. Darwish wrote:
> Peter Zijlstra <peterz@infradead.org> wrote:
> > On Tue, May 19, 2020 at 11:45:24PM +0200, Ahmed S. Darwish wrote:

> > > + WRITE_ONCE(lru_drain_gen, lru_drain_gen + 1);
> > > + smp_wmb();
> >
> > You can leave this smp_wmb() out and rely on the smp_mb() implied by
> > queue_work_on()'s test_and_set_bit().
> >
>
> Won't this be too implicit?
>
> Isn't it possible that, over the years, queue_work_on() impementation
> changes and the test_and_set_bit()/smp_mb() gets removed?
>
> If that happens, this commit will get *silently* broken and the local
> CPU pages won't be drained.

Add a comment to queue_work_on() that points here? That way people are
aware.