Re: [PATCH v2] mm: cma: support sysfs

[John Hubbard]

On 2/8/21 10:13 PM, Greg KH wrote:
> On Mon, Feb 08, 2021 at 05:57:17PM -0800, John Hubbard wrote:
> > On 2/8/21 3:36 PM, Minchan Kim wrote:
> > ...
> > > > >     	char name[CMA_MAX_NAME];
> > > > > +#ifdef CONFIG_CMA_SYSFS
> > > > > +	struct cma_stat	*stat;
> > > >
> > > > This should not be a pointer. By making it a pointer, you've added a bunch of pointless
> > > > extra code to the implementation.
> > >
> > > Originally, I went with the object lifetime with struct cma as you
> > > suggested to make code simple. However, Greg KH wanted to have
> > > release for kobj_type since it is consistent with other kboject
> > > handling.
> >
> > Are you talking about the kobj in your new struct cma_stat? That seems
> > like circular logic if so. I'm guessing Greg just wanted kobj methods
> > to be used *if* you are dealing with kobjects. That's a narrower point.
> >
> > I can't imagine that he would have insisted on having additional
> > allocations just so that kobj freeing methods could be used. :)
>
> Um, yes, I was :)
>
> You can not add a kobject to a structure and then somehow think you can
> just ignore the reference counting issues involved.  If a kobject is
> part of a structure then the kobject is responsible for controling the
> lifespan of the memory, nothing else can be.
>
> So by making the kobject dynamic, you properly handle that memory
> lifespan of the object, instead of having to worry about the lifespan of
> the larger object (which the original patch was not doing.)
>
> Does that make sense?
That part makes sense, yes, thanks. The part that I'm trying to straighten
out is, why was kobject even added to the struct cma_stat in the first
place? Why not just leave .stat as a static member variable, without
a kobject in it, and done?

thanks,
--
John Hubbard
NVIDIA