linux-kernel - Re: [PATCH v7] mm: cma: support sysfs

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Date:   Wed, 24 Mar 2021 14:55:14 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Dmitry Osipenko <digetx@...il.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, jhubbard@...dia.com,
        willy@...radead.org, Colin Ian King <colin.king@...onical.com>
Subject: Re: [PATCH v7] mm: cma: support sysfs

On Thu, Mar 25, 2021 at 12:31:51AM +0300, Dmitry Osipenko wrote:
> 24.03.2021 23:55, 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
> > failure rate for each CMA area.
> > 
> > e.g.)
> >   /sys/kernel/mm/cma/WIFI/alloc_pages_[success|fail]
> >   /sys/kernel/mm/cma/SENSOR/alloc_pages_[success|fail]
> >   /sys/kernel/mm/cma/BLUETOOTH/alloc_pages_[success|fail]
> > 
> > The cma_stat was intentionally allocated by dynamic allocation
> > to harmonize with kobject lifetime management.
> > https://lore.kernel.org/linux-mm/YCOAmXqt6dZkCQYs@kroah.com/
> > 
> > Reported-by: Dmitry Osipenko <digetx@...il.com>
> > Tested-by: Dmitry Osipenko <digetx@...il.com>
> > Suggested-by: Dmitry Osipenko <digetx@...il.com>
> 
> The tags are incorrect, I haven't suggested this change.

During the development, you have suggested many things
to make it clean. That suggested-by couldn't represent
all the detail but wanted to give credit for you, too
since you spent the time to make it better.

Okay, since you didn't like it, I will remove it.

> 
> > Suggested-by: John Hubbard <jhubbard@...dia.com>
> > Suggested-by: Matthew Wilcox <willy@...radead.org>
> > Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Reviewed-by: John Hubbard <jhubbard@...dia.com>
> 
> > Addresses-Coverity: ("Dereference after null check")
> 
> There are no dereferences fixed by this patch.

Let me add this:
https://lore.kernel.org/linux-mm/20210316100433.17665-1-colin.king@canonical.com/

> 
> > Signed-off-by: Colin Ian King <colin.king@...onical.com>
> > Signed-off-by: Minchan Kim <minchan@...nel.org>
> > ---
> ...
> 
> >  #include <linux/debugfs.h>
> > +#include <linux/kobject.h>
> > +
> > +struct cma_kobject {
> > +	struct cma *cma;
> > +	struct kobject kobj;
> 
> If you'll place the kobj as the first member of the struct, then
> container_of will be a no-op.

Cool.

> 
> ...
> > +#include <linux/cma.h>
> > +#include <linux/kernel.h>
> > +#include <linux/slab.h>
> > +
> > +#include "cma.h"
> > +
> > +void cma_sysfs_account_success_pages(struct cma *cma, unsigned long nr_pages)
> > +{
> > +	atomic64_add(nr_pages, &cma->nr_pages_succeeded);
> > +}
> > +
> > +void cma_sysfs_account_fail_pages(struct cma *cma, unsigned long nr_pages)
> > +{
> > +	atomic64_add(nr_pages, &cma->nr_pages_failed);
> > +}
> > +
> > +#define CMA_ATTR_RO(_name) \
> > +	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
> 
> nit: #defines and inlined helpers typically are placed at the top of the
> code, after includes.

No problem since I should resend anyway.

> 
> > +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;
> 
> nit: you can write this as:
> 
> return container_of(kobj, struct cma_kobject, kobj)->cma;

Better.

> 
> > +}
> > +
> > +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));
> 
> nit: Algnment isn't right, should be better to write it as single line, IMO.

Let me make it align rather than single line since I know someone
who keep asking us to not overflow 80 columns unless it's special.

> 
> ...
> > +static int __init cma_sysfs_init(void)
> > +{
> > +	struct kobject *cma_kobj_root;
> > +	struct cma_kobject *cma_kobj;
> > +	struct cma *cma;
> > +	int i, err;
> > +
> > +	cma_kobj_root = kobject_create_and_add("cma", mm_kobj);
> > +	if (!cma_kobj_root)
> > +		return -ENOMEM;
> > +
> > +	for (i = 0; i < cma_area_count; i++) {
> > +		cma_kobj = kzalloc(sizeof(*cma_kobj), GFP_KERNEL);
> > +		if (!cma_kobj) {
> > +			err = -ENOMEM;
> > +			goto out;
> > +		}
> > +
> > +		cma = &cma_areas[i];
> > +		cma->cma_kobj = cma_kobj;
> > +		cma_kobj->cma = cma;
> > +		err = kobject_init_and_add(&cma_kobj->kobj, &cma_ktype,
> > +				cma_kobj_root, "%s", cma->name);
> 
> nit: Previousy algnment of the code was better here.

Yub.

> 
> Otherwise this is okay to me:
> 
> Reviewed-by: Dmitry Osipenko <digetx@...il.com>
> Tested-by: Dmitry Osipenko <digetx@...il.com>

Thanks!