linux-kernel - Re: [PATCH v5] mm: cma: support sysfs

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Date:   Wed, 24 Mar 2021 03:02:24 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, gregkh@...uxfoundation.org,
        surenb@...gle.com, joaodias@...gle.com, jhubbard@...dia.com,
        digetx@...il.com
Subject: Re: [PATCH v5] mm: cma: support sysfs

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?

> +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.