Re: [PATCH v5] mm: cma: support sysfs

[Minchan Kim <minchan@kernel.org>]

On Wed, Mar 24, 2021 at 03:02:24AM +0000, Matthew Wilcox wrote:
> On Tue, Mar 23, 2021 at 12:50:50PM -0700, Minchan Kim wrote:
> > +	/* the number of CMA page successful allocations */
> > +	atomic64_t nr_pages_succeeded;
> 
> > +void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count)
> > +{
> > +	atomic64_add(count, &cma->nr_pages_succeeded);
> > +}
> 
> I don't understand.  A size_t is a byte count.  But the variable is called
> 'nr_pages'.  So which is it, a byte count or a page count?

It's page count. I followed the cma_alloc interface since it has
size_t count variable for nr_pages.

Let's go with unsigned long nr_pages:
void cma_sysfs_alloc_pages_count(struct cma *cma, unsigned long
nr_pages)

> 
> > +static ssize_t alloc_pages_success_show(struct kobject *kobj,
> > +					struct kobj_attribute *attr, char *buf)
> > +{
> > +	struct cma_kobject *cma_kobj = container_of(kobj,
> > +						    struct cma_kobject, kobj);
> > +	struct cma *cma = cma_kobj->cma;
> > +
> > +	return sysfs_emit(buf, "%llu\n",
> > +			  atomic64_read(&cma->nr_pages_succeeded));
> 
> ... if it's in bytes, it should probably be reported in kilobytes
> and be suffixed with a 'K' like many other stats.
>