linux-kernel - Re: [PATCH] mm: Define KB, MB, GB, TB in core VM

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Date:   Mon, 29 May 2017 13:07:10 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Christoph Hellwig <hch@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: Define KB, MB, GB, TB in core VM

Hi Anshuman,

On Wed, May 24, 2017 at 8:40 AM, Anshuman Khandual
<khandual@...ux.vnet.ibm.com> wrote:
> On 05/23/2017 04:49 PM, Anshuman Khandual wrote:
>> On 05/23/2017 02:08 PM, Vlastimil Babka wrote:
>>> On 05/23/2017 09:02 AM, Christoph Hellwig wrote:
>>>> On Mon, May 22, 2017 at 02:11:49PM -0700, Andrew Morton wrote:
>>>>> On Mon, 22 May 2017 16:47:42 +0530 Anshuman Khandual <khandual@...ux.vnet.ibm.com> wrote:
>>>>>> There are many places where we define size either left shifting integers
>>>>>> or multiplying 1024s without any generic definition to fall back on. But
>>>>>> there are couples of (powerpc and lz4) attempts to define these standard
>>>>>> memory sizes. Lets move these definitions to core VM to make sure that
>>>>>> all new usage come from these definitions eventually standardizing it
>>>>>> across all places.
>>>>> Grep further - there are many more definitions and some may now
>>>>> generate warnings.
>>>>>
>>>>> Newly including mm.h for these things seems a bit heavyweight.  I can't
>>>>> immediately think of a more appropriate place.  Maybe printk.h or
>>>>> kernel.h.
>>>> IFF we do these kernel.h is the right place.  And please also add the
>>>> MiB & co variants for the binary versions right next to the decimal
>>>> ones.
>>> Those defined in the patch are binary, not decimal. Do we even need
>>> decimal ones?
>>
>> I can define KiB, MiB, .... with the same values as binary.
>> Did not get about the decimal ones, we need different names
>> for them holding values which are multiple of 1024 ?
>
> Now it seems little bit complicated than I initially thought.
> There are three different kind of definitions scattered across
> the tree.
>
> (1) Constant defines like these which can be unified across
>     with little effort.
>
> +#define KB (1UL << 10)
> +#define MB (1UL << 20)
> +#define GB (1UL << 30)
> +#define TB (1UL << 40)

Please don't add more/generalize (ab)users of decimal prefixes where
binary prefixes are needed/intended.

https://en.wikipedia.org/wiki/Binary_prefix

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds