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Subject: Re: [PATCH v5] mm: cma: support sysfs
To:     Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        gregkh@linuxfoundation.org, surenb@google.com, joaodias@google.com,
        jhubbard@nvidia.com, willy@infradead.org
References: <20210323195050.2577017-1-minchan@kernel.org>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <bff2b424-91f7-5748-fa27-54cc75667548@gmail.com>
Date:   Wed, 24 Mar 2021 00:19:02 +0300
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23.03.2021 22:50, Minchan Kim пишет:
> Since CMA is getting used more widely, it's more important to
> keep monitoring CMA statistics for system health since it's
> directly related to user experience.
> 
> This patch introduces sysfs statistics for CMA, in order to provide
> some basic monitoring of the CMA allocator.
> 
>  * the number of CMA page successful allocations
>  * the number of CMA page allocation failures
> 
> These two values allow the user to calcuate the allocation

typo: calculate

>  struct cma {
>  	unsigned long   base_pfn;
> @@ -16,6 +22,14 @@ struct cma {
>  	struct debugfs_u32_array dfs_bitmap;
>  #endif
>  	char name[CMA_MAX_NAME];
> +#ifdef CONFIG_CMA_SYSFS
> +	/* the number of CMA page successful allocations */
> +	atomic64_t nr_pages_succeeded;
> +	/* the number of CMA page allocation failures */
> +	atomic64_t nr_pages_failed;
> +	/* kobject requires dynamic objecjt */

typo: object
...
> +static void cma_kobj_release(struct kobject *kobj)
> +{
> +	struct cma_kobject *cma_kobj =
> +		container_of(kobj, struct cma_kobject, kobj);

I'd add a to_cma_kobject() helper to improve readability.

> +	struct cma *cma = cma_kobj->cma;
> +
> +	kfree(cma_kobj);
> +	cma->kobj = NULL;
> +}
> +
> +static struct attribute *cma_attrs[] = {
> +	&alloc_pages_success_attr.attr,
> +	&alloc_pages_fail_attr.attr,
> +	NULL,
> +};
> +ATTRIBUTE_GROUPS(cma);
> +
> +static struct kobject *cma_kobj_root;
> +
> +static struct kobj_type cma_ktype = {
> +	.release = cma_kobj_release,
> +	.sysfs_ops = &kobj_sysfs_ops,
> +	.default_groups = cma_groups
> +};
> +
> +static int __init cma_sysfs_init(void)
> +{
> +	int i = 0;

unsigned int, for consistency

There is no need to initialize this variable.

> +	struct cma *cma;
> +
> +	cma_kobj_root = kobject_create_and_add("cma", mm_kobj);
> +	if (!cma_kobj_root)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < cma_area_count; i++) {
> +		struct cma_kobject *kobj;
> +
> +		cma = &cma_areas[i];
> +		kobj = kzalloc(sizeof(struct cma_kobject), GFP_KERNEL);

Checkpatch should warn that kzalloc(*kobj, ..) is a better variant.

I'd also rename kobj to cma_kobj everywhere, for clarity.

> +		if (!kobj)
> +			goto out;
> +
> +		kobj->cma = cma;
> +		cma->kobj = kobj;
> +		if (kobject_init_and_add(&cma->kobj->kobj, &cma_ktype,
> +					 cma_kobj_root, "%s", cma->name)) {
> +			kobject_put(&cma->kobj->kobj);
> +			goto out;
> +		}
> +	}
> +
> +	return 0;
> +out:
> +	kobject_put(cma_kobj_root);
> +
> +	return -ENOMEM;

kobject_init_and_add returns a error code, it could be different from
ENOMEM. Won't hurt to propagate the proper error code.