Re: [PATCH v4] mm: cma: support sysfs

[Greg Kroah-Hartman]

On Fri, Mar 19, 2021 at 10:24:03PM +0300, Dmitry Osipenko wrote:
> 19.03.2021 22:03, Minchan Kim пишет:
> > On Fri, Mar 19, 2021 at 09:48:11PM +0300, Dmitry Osipenko wrote:
> >> 19.03.2021 21:21, Minchan Kim пишет:
> >>> On Fri, Mar 19, 2021 at 08:56:06PM +0300, Dmitry Osipenko wrote:
> >>>> 19.03.2021 19:30, Minchan Kim пишет:
> >>>>> +static void cma_kobj_release(struct kobject *kobj)
> >>>>> +{
> >>>>> +	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject, kobj);
> >>>>> +
> >>>>> +	kfree(cma_kobj);
> >>>>> +}
> >>>>
> >>>> Oh, wait.. I think this kfree wrong since cma_kobj belongs to the array.
> >>>
> >>> Oh, good spot. Let me use kzalloc.
> >>>
> >>
> >> Thinking a bit more about this.. it looks like actually it should be
> >> better to get back to the older variant of cma_stat, but allocate at the
> >> time of CMA initialization, rather than at the time of sysfs
> >> initialization. Then the cma_stat will be decoupled from the cma struct
> > 
> > IIRC, the problem was slab was not initiaized at CMA init point.
> > That's why I liked your suggestion.
> 
> Alright, if CMA init time is a problem, then the recent variant should
> be okay.
> 
> >> and cma_stat will be a self-contained object.
> > 
> > Yeah, self-contained is better but it's already weird to
> > have differnt lifetime for one object since CMA object
> > never die, technically.
> > 
> 
> Indeed.
> 
> I found the Greg's original argument and not sure that it's really
> worthwhile to worry about the copycats since this is not a driver's code..
> 
> Maybe we could just add a clarifying comment for the kobj, telling why
> it's okay for CMA. Greg, doesn't it sound like a good compromise to you?

Please no.