linux-kernel - Re: [PATCH] mm: change "char *bdi_unknown_name" to "char bdi_unknown

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Message-Id: <20220512130051.94a0c53e5d1498292473975d@linux-foundation.org>
Date:   Thu, 12 May 2022 13:00:51 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     liqiong <liqiong@...china.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: change "char *bdi_unknown_name" to
 "char bdi_unknown_name[]"

On Thu, 12 May 2022 16:26:37 +0800 liqiong <liqiong@...china.com> wrote:

> "char bdi_unknown_nam[]" string form declares a single variable.
> It is better then "char *bdi_unknown_name" which creates two
> variables.
> 
> ...
>
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -20,7 +20,7 @@ struct backing_dev_info noop_backing_dev_info;
>  EXPORT_SYMBOL_GPL(noop_backing_dev_info);
>  
>  static struct class *bdi_class;
> -static const char *bdi_unknown_name = "(unknown)";
> +static const char bdi_unknown_name[] = "(unknown)";
>  

heh, fun patch.  We actually do this quite a lot.  

	grep -r "^[a-z].*char \*[a-z].*= \"" .

is a pathetic pattern which catches a lot of them.


However.  I expected your patch to shrink the kernel a bit, but it has
the opposite effect:

hp2:/usr/src/25> size mm/backing-dev.o
   text	   data	    bss	    dec	    hex	filename
  21288	   9396	   3808	  34492	   86bc	mm/backing-dev.o-before
  21300	   9428	   3808	  34536	   86e8	mm/backing-dev.o-after

Even .data became larger.  I didn't investigate why.