Re: [External] Re: [PATCH 0/3] mm: replace atomic_t with percpu_ref in mempolicy.

[Zhongkun He]

> On Mon 05-12-22 00:14:29, Zhongkun He wrote:
> [...]
> > +/* Obtain a reference on the specified mpol */
> >   static inline void mpol_get(struct mempolicy *pol)
> >   {
> >   	if (pol)
>
> Shouldn't this be mpol_needs_cond_ref?
>
> > -		atomic_inc(&pol->refcnt);
> > +		percpu_ref_get(&pol->refcnt);
> > +}
> > +
> > +static inline bool mpol_tryget(struct mempolicy *pol)
> > +{
> > +	return pol && percpu_ref_tryget(&pol->refcnt);
> >   }
> >   
> > +/*
> > + * This function initiates destruction of mempolicy.
>
> This is not a useful comment. It would be much more helpful to say when
> this should be called.
>
> > + */
> > +static inline void mpol_kill(struct mempolicy *pol)
> > +{
> > +        if (pol)
> > +                percpu_ref_kill(&pol->refcnt);
> > +}
> > +
> > +
> >   extern bool __mpol_equal(struct mempolicy *a, struct mempolicy *b);
> >   static inline bool mpol_equal(struct mempolicy *a, struct mempolicy *b)
> >   {
> > @@ -197,11 +210,15 @@ static inline void mpol_put(struct mempolicy *p)
> >   {
> >   }
> >   
> > -static inline void mpol_cond_put(struct mempolicy *pol)
> > +static inline void mpol_get(struct mempolicy *pol)
> >   {
> >   }
> >   
> > -static inline void mpol_get(struct mempolicy *pol)
> > +static inline bool mpol_tryget(struct mempolicy *pol)
> > +{
> > +}
>
> This should return false, right?
>
> [...]
> > +/* Obtain a reference on the specified task mempolicy */
>
> Again, this is pretty much clear from the name. It would be more useful
> to explain how the pointer can be used - e.g. needs to call mpol_put
> or mpol_kill depending on the calling context.
>
> > +static mempolicy *get_task_mpol(struct task_struct *p)
> > +{
> > +	struct mempolicy *pol;
> > +
> > +	rcu_read_lock();
> > +	pol = rcu_dereference(p->mempolicy);
> > +
> > +	if (!pol || mpol_tryget(pol))
>
> Shouldn't be !mpol_tryget?
>
> > +		pol = NULL;
> > +	rcu_read_unlock();
> > +
> > +	return pol;
> > +}
> > +
>
> I do not see any rcu_assign_pointer for the newly created policy so this
> seems incomplete. Ditto no mpol_kill calls. I am unlikely to get into
> follow up patches now. Please split up the work so that it is reviewable
> more easily and then I can have a further look.
>
> Thanks!

Thanks for your review, some changes may be in other patch,i will
reorganize the patches according to the suggestions to make
things clear.

Thanks.