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

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Message-ID: <20210205025526.GG308988@casper.infradead.org>
Date:   Fri, 5 Feb 2021 02:55:26 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        gregkh@...uxfoundation.org, surenb@...gle.com, joaodias@...gle.com,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] mm: cma: support sysfs

On Wed, Feb 03, 2021 at 07:50:01AM -0800, Minchan Kim wrote:
> +++ b/mm/Makefile
> @@ -106,6 +106,7 @@ obj-$(CONFIG_ZSMALLOC)	+= zsmalloc.o
>  obj-$(CONFIG_Z3FOLD)	+= z3fold.o
>  obj-$(CONFIG_GENERIC_EARLY_IOREMAP) += early_ioremap.o
>  obj-$(CONFIG_CMA)	+= cma.o
> +obj-$(CONFIG_SYSFS)     += cma_sysfs.o

ehh ... if we have a kernel build with CMA=n, SYSFS=y, we'll get
cma_sysfs built in with no cma to report on.

> +static ssize_t cma_alloc_attempt_show(struct kobject *kobj,
> +			struct kobj_attribute *attr, char *buf)
> +{
> +	unsigned long val;
> +	struct cma_stat *stat = container_of(kobj, struct cma_stat, kobj);
> +
> +	val = stat->alloc_attempt;
> +
> +	return sysfs_emit(buf, "%lu\n", val);

Why not more simply:

{
	struct cma_stat *stat = container_of(kobj, struct cma_stat, kobj);
	return sysfs_emit(buf, "%lu\n", stat->alloc_attempt);
}

> +	for (i = 0; i < cma_area_count; i++) {
> +		cma = &cma_areas[i];
> +		stat = kzalloc(sizeof(*stat), GFP_KERNEL);
> +		if (!stat)
> +			goto out;

How many cma areas are there going to be?  do we really want to allocate
their stat individually?