linux-kernel - Re: [PATCH v1 1/6] mm: Section numbers use the type "unsigned long"

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Date:   Sat, 15 Jun 2019 10:06:54 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Michal Hocko <mhocko@...e.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Baoquan He <bhe@...hat.com>, linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, Wei Yang <richard.weiyang@...il.com>,
        linux-acpi@...r.kernel.org,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Arun KS <arunks@...eaurora.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        linuxppc-dev@...ts.ozlabs.org, Vlastimil Babka <vbabka@...e.cz>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v1 1/6] mm: Section numbers use the type "unsigned long"



Le 14/06/2019 à 21:00, Andrew Morton a écrit :
> On Fri, 14 Jun 2019 12:01:09 +0200 David Hildenbrand <david@...hat.com> wrote:
> 
>> We are using a mixture of "int" and "unsigned long". Let's make this
>> consistent by using "unsigned long" everywhere. We'll do the same with
>> memory block ids next.
>>
>> ...
>>
>> -	int i, ret, section_count = 0;
>> +	unsigned long i;
>>
>> ...
>>
>> -	unsigned int i;
>> +	unsigned long i;
> 
> Maybe I did too much fortran back in the day, but I think the
> expectation is that a variable called "i" has type "int".
> 
> This?
> 
> 
> 
> s/unsigned long i/unsigned long section_nr/

 From my point of view you degrade readability by doing that.

section_nr_to_pfn(mem->start_section_nr + section_nr);

Three times the word 'section_nr' in one line, is that worth it ? Gives 
me headache.

Codying style says the following, which makes full sense in my opinion:

LOCAL variable names should be short, and to the point.  If you have
some random integer loop counter, it should probably be called ``i``.
Calling it ``loop_counter`` is non-productive, if there is no chance of it
being mis-understood.

What about just naming it 'nr' if we want to use something else than 'i' ?

Christophe


> 
> --- a/drivers/base/memory.c~mm-section-numbers-use-the-type-unsigned-long-fix
> +++ a/drivers/base/memory.c
> @@ -131,17 +131,17 @@ static ssize_t phys_index_show(struct de
>   static ssize_t removable_show(struct device *dev, struct device_attribute *attr,
>   			      char *buf)
>   {
> -	unsigned long i, pfn;
> +	unsigned long section_nr, pfn;
>   	int ret = 1;
>   	struct memory_block *mem = to_memory_block(dev);
>   
>   	if (mem->state != MEM_ONLINE)
>   		goto out;
>   
> -	for (i = 0; i < sections_per_block; i++) {
> -		if (!present_section_nr(mem->start_section_nr + i))
> +	for (section_nr = 0; section_nr < sections_per_block; section_nr++) {
> +		if (!present_section_nr(mem->start_section_nr + section_nr))
>   			continue;
> -		pfn = section_nr_to_pfn(mem->start_section_nr + i);
> +		pfn = section_nr_to_pfn(mem->start_section_nr + section_nr);
>   		ret &= is_mem_section_removable(pfn, PAGES_PER_SECTION);
>   	}
>   
> @@ -695,12 +695,12 @@ static int add_memory_block(unsigned lon
>   {
>   	int ret, section_count = 0;
>   	struct memory_block *mem;
> -	unsigned long i;
> +	unsigned long section_nr;
>   
> -	for (i = base_section_nr;
> -	     i < base_section_nr + sections_per_block;
> -	     i++)
> -		if (present_section_nr(i))
> +	for (section_nr = base_section_nr;
> +	     section_nr < base_section_nr + sections_per_block;
> +	     section_nr++)
> +		if (present_section_nr(section_nr))
>   			section_count++;
>   
>   	if (section_count == 0)
> @@ -823,7 +823,7 @@ static const struct attribute_group *mem
>    */
>   int __init memory_dev_init(void)
>   {
> -	unsigned long i;
> +	unsigned long section_nr;
>   	int ret;
>   	int err;
>   	unsigned long block_sz;
> @@ -840,9 +840,9 @@ int __init memory_dev_init(void)
>   	 * during boot and have been initialized
>   	 */
>   	mutex_lock(&mem_sysfs_mutex);
> -	for (i = 0; i <= __highest_present_section_nr;
> -		i += sections_per_block) {
> -		err = add_memory_block(i);
> +	for (section_nr = 0; section_nr <= __highest_present_section_nr;
> +		section_nr += sections_per_block) {
> +		err = add_memory_block(section_nr);
>   		if (!ret)
>   			ret = err;
>   	}
> _
>