linux-kernel - Re: [PATCH] mm/page_alloc: fix documentation error and remove magic numbers

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Date:   Wed, 24 Jun 2020 10:26:26 -0400
From:   Rafael Aquini <aquini@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Joel Savitz <jsavitz@...hat.com>, linux-kernel@...r.kernel.org,
        Vlastimil Babka <vbabka@...e.cz>,
        John Hubbard <jhubbard@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Subject: Re: [PATCH] mm/page_alloc: fix documentation error and remove magic
 numbers

On Wed, Jun 24, 2020 at 03:09:58PM +0100, Matthew Wilcox wrote:
> On Wed, Jun 24, 2020 at 10:07:27AM -0400, Rafael Aquini wrote:
> > On Wed, Jun 24, 2020 at 12:12:55PM +0100, Matthew Wilcox wrote:
> > > On Tue, Jun 23, 2020 at 11:27:12PM -0400, Joel Savitz wrote:
> > > > In addition, this patch replaces the magic number bounds with symbolic
> > > > constants to clarify the logic.
> > > 
> > > Why do people think this kind of thing makes the code easier to read?
> > > It actually makes it harder.  Unless the constants are used in more
> > > than one place, just leave the numbers where they are.
> > > 
> > > > @@ -7852,6 +7852,9 @@ void setup_per_zone_wmarks(void)
> > > >   * 8192MB:	11584k
> > > >   * 16384MB:	16384k
> > > >   */
> > > > +static const int MIN_FREE_KBYTES_LOWER_BOUND = 1 << 7;
> > > > +static const int MIN_FREE_KBYTES_UPPER_BOUND = 1 << 18;
> > > > +
> > 
> > I think these constants would look better if declared as an enum.
> 
> Why does having to look in two different places make the code clearer?
>

It might not make it clearer in this particular case, because it was
easy to take the meaning from the code, but it also doesn't make it
harder to read, so I don't have any strong opinion on this case. 

Joel's approach, however, makes sense if you consider it's generally a 
good practice to get rid of the unnamed magic numbers anti-pattern.

Cheers,
-- Rafael