linux-kernel - Re: [PATCH 2/6] mm/page_alloc.c: simplify the code by using macro K()

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Date:   Tue, 31 Aug 2021 19:08:42 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Oleksandr Natalenko <oleksandr@...alenko.name>
CC:     <vbabka@...e.cz>, <sfr@...b.auug.org.au>, <peterz@...radead.org>,
        <mgorman@...hsingularity.net>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/6] mm/page_alloc.c: simplify the code by using macro K()

On 2021/8/31 16:54, Oleksandr Natalenko wrote:
> Hello.
> 
> On pondělí 30. srpna 2021 16:10:47 CEST Miaohe Lin wrote:
>> Use helper macro K() to convert the pages to the corresponding size.
>> Minor readability improvement.
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>> ---
>>  mm/page_alloc.c | 12 +++++-------
>>  1 file changed, 5 insertions(+), 7 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index dbb3338d9287..d3983244f56f 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -8134,8 +8134,7 @@ unsigned long free_reserved_area(void *start, void
>> *end, int poison, const char }
>>
>>  	if (pages && s)
>> -		pr_info("Freeing %s memory: %ldK\n",
>> -			s, pages << (PAGE_SHIFT - 10));
>> +		pr_info("Freeing %s memory: %ldK\n", s, K(pages));
>>
>>  	return pages;
>>  }
>> @@ -8180,14 +8179,13 @@ void __init mem_init_print_info(void)
>>  		", %luK highmem"
>>  #endif
>>  		")\n",
>> -		nr_free_pages() << (PAGE_SHIFT - 10),
>> -		physpages << (PAGE_SHIFT - 10),
>> +		K(nr_free_pages()), K(physpages),
>>  		codesize >> 10, datasize >> 10, rosize >> 10,
>>  		(init_data_size + init_code_size) >> 10, bss_size >> 10,
>> -		(physpages - totalram_pages() - totalcma_pages) << (PAGE_SHIFT 
> - 10),
>> -		totalcma_pages << (PAGE_SHIFT - 10)
>> +		K(physpages - totalram_pages() - totalcma_pages),
>> +		K(totalcma_pages)
>>  #ifdef	CONFIG_HIGHMEM
>> -		, totalhigh_pages() << (PAGE_SHIFT - 10)
>> +		, K(totalhigh_pages())
>>  #endif
>>  		);
>>  }
> 
> (my concern is not quite within the scope of this submission, but I'll ask 
> anyway)
> 
> Given we have this:
> 
> ```
> git grep '#define K(x)' v5.14
> v5.14:drivers/base/node.c:#define K(x) ((x) << (PAGE_SHIFT - 10))
> v5.14:drivers/net/hamradio/scc.c:#define K(x) kiss->x
> v5.14:kernel/debug/kdb/kdb_main.c:#define K(x) ((x) << (PAGE_SHIFT - 10))
> v5.14:mm/backing-dev.c:#define K(x) ((x) << (PAGE_SHIFT - 10))
> v5.14:mm/memcontrol.c:#define K(x) ((x) << (PAGE_SHIFT-10))
> v5.14:mm/oom_kill.c:#define K(x) ((x) << (PAGE_SHIFT-10))
> v5.14:mm/page_alloc.c:#define K(x) ((x) << (PAGE_SHIFT-10))
> ```
> 
> Shouldn't this macro go to some header file instead to get rid of define 
> repetitions?

Many thanks for figuring this out. I think we should get rid of these repetitions too.
But I'am not sure where this definition should be. Any suggestion? Thanks.

> 
> Thanks.
>