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

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Date:   Wed, 01 Sep 2021 09:46:17 +0200
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     Miaohe Lin <linmiaohe@...wei.com>
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()

Hello.

On středa 1. září 2021 9:37:49 CEST Miaohe Lin wrote:
> On 2021/8/31 22:19, Oleksandr Natalenko wrote:
> > On úterý 31. srpna 2021 13:08:42 CEST Miaohe Lin wrote:
> >> On 2021/8/31 16:54, Oleksandr Natalenko wrote:
> >>> 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.
> > 
> > I'm not sure what place suits best. At first I thought maybe linux/mm.h or
> > linux/mm_inline.h, but since PAGE_SHIFT is declared in asm-generic/page.h,
> > probably K(x) can also go there as well?
> 
> K(x) is relevant with PAGE_SHIFT. So I think K(x) can also go
> asm-generic/page.h too.

Actually, the comment in this file says:

```
4 /*
5  * Generic page.h implementation, for NOMMU architectures.
6  * This provides the dummy definitions for the memory management.
7  */
```

so it seems I was wrong about this being an appropriate place.

> Am I supposed to do this when free or will you
> kindly do this?

Let me just try to cram this into mm.h and send it out, and then we'll see 
what comments people suggest.

Thanks.

-- 
Oleksandr Natalenko (post-factum)