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Sender: Minchan Kim <minchan.kim@gmail.com>
Date:   Tue, 23 Mar 2021 20:31:31 -0700
From:   Minchan Kim <minchan@kernel.org>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        linux-mm <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>, gregkh@linuxfoundation.org,
        surenb@google.com, joaodias@google.com, jhubbard@nvidia.com,
        digetx@gmail.com
Subject: Re: [PATCH v5] mm: cma: support sysfs
Message-ID: <YFqyk0/yXs2kMP76@google.com>
References: <20210323195050.2577017-1-minchan@kernel.org>
 <20210324030224.GO1719932@casper.infradead.org>
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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.
>