Re: [PATCH V6 1/2] percpu_ref: reduce memory footprint of percpu_ref in fast path

From: Ming Lei
Date: Thu Oct 01 2020 - 11:38:31 EST


On Wed, Sep 30, 2020 at 12:00:15PM -0400, Tejun Heo wrote:
> On Wed, Sep 30, 2020 at 04:26:56PM +0800, Ming Lei wrote:
> > diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
> > index 87d8a38bdea1..1d6ed9ca23dd 100644
> > --- a/include/linux/percpu-refcount.h
> > +++ b/include/linux/percpu-refcount.h
> > @@ -92,18 +92,23 @@ enum {
> > PERCPU_REF_ALLOW_REINIT = 1 << 2,
> > };
> >
> > -struct percpu_ref {
> > +struct percpu_ref_data {
> > atomic_long_t count;
> > - /*
> > - * The low bit of the pointer indicates whether the ref is in percpu
> > - * mode; if set, then get/put will manipulate the atomic_t.
> > - */
> > - unsigned long percpu_count_ptr;
> > percpu_ref_func_t *release;
> > percpu_ref_func_t *confirm_switch;
> > bool force_atomic:1;
> > bool allow_reinit:1;
> > struct rcu_head rcu;
> > + struct percpu_ref *ref;
> > +};
> > +
> > +struct percpu_ref {
> > + /*
> > + * The low bit of the pointer indicates whether the ref is in percpu
> > + * mode; if set, then get/put will manipulate the atomic_t.
> > + */
> > + unsigned long percpu_count_ptr;
> > + struct percpu_ref_data *data;
> > };
>
> Can you please add a comment explaining why the two structs are split?

Sure, will do that in next version.

Thanks,
Ming