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 16:19:23 +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 úterý 31. srpna 2021 13:08:42 CEST Miaohe Lin wrote:
> 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.

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?

-- 
Oleksandr Natalenko (post-factum)