Re: [PATCH 19/24] rcu/tree: Support reclaim for head-less object

Paul E. McKenney
2020-05-04T17:08:35Z

On Mon, May 04, 2020 at 06:56:29PM +0200, Uladzislau Rezki wrote:
> > >
> > > For single argument we can drop the lock before the entry to the page
> > > allocator. Because it follows might_sleep() anotation we avoid of having
> > > a situation when spinlock(rt mutex) is taken from any atomic context.
> > >
> > > Since the lock is dropped the current context can be interrupted by
> > > an IRQ which in its turn can also call kvfree_rcu() on current CPU.
> > > In that case it must be double argument(single is not allowed) kvfree_rcu()
> > > call. For PREEMPT_RT if no cache everything is reverted to rcu_head usage,
> > > i.e. the entry to page allocator is bypassed.
> > >
> > > It can be addressed as a separate patch and send out later on if we
> > > are on the same page.
> > >
> > > Paul, Joel what are your opinions?
> >
> > I strongly prefer that it be removed from the series. I do understand
> > that this is a bit more hassle right now, but this does help avoid
> > confusion in the future, plus perhaps also avoiding issues with future
> > bisections.
> >
> We have already decided to get rid of it, i mean small allocations(dynamic
> rcu_head attaching). I will exclude it from next patch-set version.

Very good, and thank you!!!

Thanx, Paul