Re: [PATCH v2 2/5] huge_memory: add huge_zero_page_shrinker_(init|exit) function

["Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>]

On Tue, Jul 15, 2025 at 03:29:08PM +0100, Lorenzo Stoakes wrote:
> Nit on subject, function -> functions.
> 
> On Mon, Jul 07, 2025 at 04:23:16PM +0200, Pankaj Raghav (Samsung) wrote:
> > From: Pankaj Raghav <p.raghav@samsung.com>
> >
> > Add huge_zero_page_shrinker_init() and huge_zero_page_shrinker_exit().
> > As shrinker will not be needed when static PMD zero page is enabled,
> > these two functions can be a no-op.
> >
> > This is a preparation patch for static PMD zero page. No functional
> > changes.
> 
> This is nitty stuff, but I think this is a little unclear, maybe something
> like:
> 
> 	We will soon be determining whether to use a shrinker depending on
> 	whether a static PMD zero page is available, therefore abstract out
> 	shrink initialisation and teardown such that we can more easily
> 	handle both the shrinker and static PMD zero page cases.
> 
This looks good. I will use add this to the commit message.

> >
> > Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> 
> Other than nits, this LGTM, so with those addressed:
> 
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

Thanks.

> >  #ifdef CONFIG_SYSFS
> >  static ssize_t enabled_show(struct kobject *kobj,
> > @@ -850,33 +868,31 @@ static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
> >
> >  static int __init thp_shrinker_init(void)
> >  {
> > -	huge_zero_page_shrinker = shrinker_alloc(0, "thp-zero");
> > -	if (!huge_zero_page_shrinker)
> > -		return -ENOMEM;
> > +	int ret = 0;
> 
> Kinda no point in initialising to zero, unless...
> 
> >
> >  	deferred_split_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE |
> >  						 SHRINKER_MEMCG_AWARE |
> >  						 SHRINKER_NONSLAB,
> >  						 "thp-deferred_split");
> > -	if (!deferred_split_shrinker) {
> > -		shrinker_free(huge_zero_page_shrinker);
> > +	if (!deferred_split_shrinker)
> >  		return -ENOMEM;
> > -	}
> > -
> > -	huge_zero_page_shrinker->count_objects = shrink_huge_zero_page_count;
> > -	huge_zero_page_shrinker->scan_objects = shrink_huge_zero_page_scan;
> > -	shrinker_register(huge_zero_page_shrinker);
> >
> >  	deferred_split_shrinker->count_objects = deferred_split_count;
> >  	deferred_split_shrinker->scan_objects = deferred_split_scan;
> >  	shrinker_register(deferred_split_shrinker);
> >
> > +	ret = huge_zero_page_shrinker_init();
> > +	if (ret) {
> > +		shrinker_free(deferred_split_shrinker);
> > +		return ret;
> > +	}
> 
> ... you change this to:
> 
> 	if (ret)
> 		shrinker_free(deferred_split_shrinker);
> 
> 	return ret;
> 
> But it's not a big deal. Maybe I'd rename ret -> err if you keep things as
> they are (but don't init to 0).

Sounds good.

--
Pankaj