linux-kernel - Re: [PATCH v1] mm:Using div64_ul replaces do

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Date:   Fri, 16 Jun 2023 12:52:19 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Wang Ming <machel@...o.com>
Cc:     Mike Rapoport <rppt@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, opensource.kernel@...o.com
Subject: Re: [PATCH v1] mm:Using div64_ul replaces do_div() function

On Thu, 15 Jun 2023 15:51:14 +0800 Wang Ming <machel@...o.com> wrote:

> Fix the following coccicheck warning:
> 
> mm/mm_init.c:2492:2-8: WARNING: do_div() does a
> 64-by-32 division, please consider using div64_ul instead.

I guess coccicheck was fooled by the incorrect comment over do_div(). 
do_div() returns an unsigned long.

alloc_large_system_hash() should be using a u64 for `max'.  Nobody uses
unsigned long long any more.

> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -2508,7 +2508,7 @@ void *__init alloc_large_system_hash(const char *tablename,
>         /* limit allocation size to 1/16 total memory by default */
>         if (max == 0) {
>                 max = ((unsigned long long)nr_all_pages << PAGE_SHIFT) >> 4;
> -               do_div(max, bucketsize);
> +               div64_ul(max, bucketsize);
>         }
>         max = min(max, 0x80000000ULL);