linux-kernel - Re: [PATCH v6] mm: cma: support sysfs

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Date:   Tue, 23 Mar 2021 20:27:23 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     John Hubbard <jhubbard@...dia.com>
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, willy@...radead.org,
        digetx@...il.com
Subject: Re: [PATCH v6] mm: cma: support sysfs

On Tue, Mar 23, 2021 at 07:34:12PM -0700, John Hubbard wrote:
> On 3/23/21 6:05 PM, Minchan Kim wrote:
> ...> diff --git a/mm/cma_sysfs.c b/mm/cma_sysfs.c
> > new file mode 100644
> > index 000000000000..c3791a032dc5
> > --- /dev/null
> > +++ b/mm/cma_sysfs.c
> > @@ -0,0 +1,107 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * CMA SysFS Interface
> > + *
> > + * Copyright (c) 2021 Minchan Kim <minchan@...nel.org>
> > + */
> > +
> > +#include <linux/cma.h>
> > +#include <linux/kernel.h>
> > +#include <linux/slab.h>
> > +
> > +#include "cma.h"
> > +
> > +void cma_sysfs_account_success_pages(struct cma *cma, size_t count)
> > +{
> > +	atomic64_add(count, &cma->nr_pages_succeeded);
> > +}
> > +
> > +void cma_sysfs_account_fail_pages(struct cma *cma, size_t count)
> > +{
> > +	atomic64_add(count, &cma->nr_pages_failed);
> > +}
> > +
> > +#define CMA_ATTR_RO(_name) \
> > +	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
> > +
> > +#define to_cma_kobject(x) container_of(x, struct cma_kobject, kobj)
> 
> I really don't think that helps. container_of() is so widely used and
> understood that it is not a good move make people read one more wrapper
> for it. Instead, see below...
> 
> > +
> > +static ssize_t alloc_pages_success_show(struct kobject *kobj,
> > +					struct kobj_attribute *attr, char *buf)
> > +{
> > +	struct cma_kobject *cma_kobj = to_cma_kobject(kobj);
> > +	struct cma *cma = cma_kobj->cma;
> 
> ...if you're looking to get rid of the real code duplication, then you
> could put *both* of those lines into a wrapper function, instead, like this:
> 
> static inline struct cma* cma_from_kobj(struct kobject *kobj)
> {
> 	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject,
> 						    kobj);
> 	struct cma *cma = cma_kobj->cma;
> 
> 	return cma;
> }
> 
> static ssize_t alloc_pages_success_show(struct kobject *kobj,
> 					struct kobj_attribute *attr, char *buf)
> {
> 	struct cma *cma = cma_from_kobj(kobj);
> 
> 	return sysfs_emit(buf, "%llu\n",
> 			  atomic64_read(&cma->nr_pages_succeeded));
> }
> CMA_ATTR_RO(alloc_pages_success);
> 
> static ssize_t alloc_pages_fail_show(struct kobject *kobj,
> 				     struct kobj_attribute *attr, char *buf)
> {
> 	struct cma *cma = cma_from_kobj(kobj);
> 
> 	return sysfs_emit(buf, "%llu\n", atomic64_read(&cma->nr_pages_failed));
> }
> CMA_ATTR_RO(alloc_pages_fail);
> 
> static void cma_kobj_release(struct kobject *kobj)
> {
> 	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject,
> 						    kobj);
> 	struct cma *cma = cma_kobj->cma;
> 
> 	kfree(cma_kobj);
> 	cma->kobj = NULL;
> }
> 
> ...isn't that nicer? Saves a little code, gets rid of a macro.

Yub.

> 
> > +
> > +	return sysfs_emit(buf, "%llu\n",
> > +			  atomic64_read(&cma->nr_pages_succeeded));
> > +}
> > +CMA_ATTR_RO(alloc_pages_success);
> > +
> > +static ssize_t alloc_pages_fail_show(struct kobject *kobj,
> > +				     struct kobj_attribute *attr, char *buf)
> > +{
> > +	struct cma_kobject *cma_kobj = to_cma_kobject(kobj);
> > +	struct cma *cma = cma_kobj->cma;
> > +
> > +	return sysfs_emit(buf, "%llu\n", atomic64_read(&cma->nr_pages_failed));
> > +}
> > +CMA_ATTR_RO(alloc_pages_fail);
> > +
> > +static void cma_kobj_release(struct kobject *kobj)
> > +{
> > +	struct cma_kobject *cma_kobj = to_cma_kobject(kobj);
> > +	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)
> > +{
> > +	unsigned int i;
> > +
> > +	cma_kobj_root = kobject_create_and_add("cma", mm_kobj);
> > +	if (!cma_kobj_root)
> > +		return -ENOMEM;
> > +
> > +	for (i = 0; i < cma_area_count; i++) {
> > +		int err;
> > +		struct cma *cma;
> > +		struct cma_kobject *cma_kobj;
> > +
> > +		cma_kobj = kzalloc(sizeof(*cma_kobj), GFP_KERNEL);
> > +		if (!cma_kobj) {
> > +			kobject_put(cma_kobj_root);
> > +			return -ENOMEM;
> 
> This leaks little cma_kobj's all over the floor. :)

I thought kobject_put(cma_kobj_root) should deal with it. No?

> 
> What you might want here is a separate routine to clean up, because
> it has to loop through and free whatever was allocated on previous
> iterations of this loop here.
> 
> > +		}
> > +
> > +		cma = &cma_areas[i];
> > +		cma->kobj = cma_kobj;
> > +		cma_kobj->cma = cma;
> > +		err = kobject_init_and_add(&cma_kobj->kobj, &cma_ktype,
> > +					   cma_kobj_root, "%s", cma->name);
> > +		if (err) {
> > +			kobject_put(&cma_kobj->kobj);
> > +			kobject_put(cma_kobj_root);
> > +			return err;
> 
> Hopefully this little bit of logic could also go into the cleanup
> routine.
> 
> > +		}
> > +	}
> > +
> > +	return 0;
> > +}
> > +subsys_initcall(cma_sysfs_init);
> > 
> 
> thanks,
> -- 
> John Hubbard
> NVIDIA