From: Bart Van Assche <bvanassche@acm.org>
To: Alexander Duyck <alexander.duyck@gmail.com>
Cc: linux@rasmusvillemoes.dk,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
Vlastimil Babka <vbabka@suse.cz>,
Mel Gorman <mgorman@techsingularity.net>,
Christoph Lameter <cl@linux.com>,
guro@fb.com, Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
linux-mm <linux-mm@kvack.org>
Subject: Re: [PATCH] slab.h: Avoid using & for logical and of booleans
Date: Tue, 06 Nov 2018 09:48:41 -0800 [thread overview]
Message-ID: <1541526521.196084.184.camel@acm.org> (raw)
In-Reply-To: <CAKgT0UekDV4euPHs-wrZixGN1ryhZBq_42XdK6BapYke_xomJg@mail.gmail.com>
On Tue, 2018-11-06 at 09:20 -0800, Alexander Duyck wrote:
> On Mon, Nov 5, 2018 at 4:32 PM Bart Van Assche <bvanassche@acm.org> wrote:
> >
> > On Mon, 2018-11-05 at 16:11 -0800, Alexander Duyck wrote:
> > > If we really don't care then why even bother with the switch statement
> > > anyway? It seems like you could just do one ternary operator and be
> > > done with it. Basically all you need is:
> > > return (defined(CONFIG_ZONE_DMA) && (flags & __GFP_DMA)) ? KMALLOC_DMA :
> > > (flags & __GFP_RECLAIMABLE) ? KMALLOC_RECLAIM : 0;
> > >
> > > Why bother with all the extra complexity of the switch statement?
> >
> > I don't think that defined() can be used in a C expression. Hence the
> > IS_ENABLED() macro. If you fix that, leave out four superfluous parentheses,
> > test your patch, post that patch and cc me then I will add my Reviewed-by.
>
> Actually the defined macro is used multiple spots in if statements
> throughout the kernel.
The only 'if (defined(' matches I found in the kernel tree that are not
preprocessor statements occur in Perl code. Maybe I overlooked something?
> The reason for IS_ENABLED is to address the fact that we can be
> dealing with macros that indicate if they are built in or a module
> since those end up being two different defines depending on if you
> select 'y' or 'm'.
From Documentation/process/coding-style.rst:
Within code, where possible, use the IS_ENABLED macro to convert a Kconfig
symbol into a C boolean expression, and use it in a normal C conditional:
.. code-block:: c
if (IS_ENABLED(CONFIG_SOMETHING)) {
...
}
Bart.
next prev parent reply other threads:[~2018-11-06 17:48 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-05 20:40 [PATCH] slab.h: Avoid using & for logical and of booleans Bart Van Assche
2018-11-05 21:13 ` Andrew Morton
2018-11-05 21:48 ` Bart Van Assche
2018-11-05 22:14 ` Rasmus Villemoes
2018-11-05 22:40 ` Bart Van Assche
2018-11-05 22:48 ` Alexander Duyck
2018-11-06 0:01 ` Bart Van Assche
2018-11-06 0:11 ` Alexander Duyck
2018-11-06 0:32 ` Bart Van Assche
2018-11-06 17:20 ` Alexander Duyck
2018-11-06 17:48 ` Bart Van Assche [this message]
2018-11-06 18:17 ` Alexander Duyck
2018-11-06 9:45 ` William Kucharski
2018-11-06 8:40 ` Vlastimil Babka
2018-11-06 10:08 ` David Laight
2018-11-06 10:22 ` Vlastimil Babka
2018-11-06 11:07 ` David Laight
2018-11-06 12:51 ` Vlastimil Babka
2018-11-07 10:41 ` David Laight
2018-11-09 8:12 ` Vlastimil Babka
2018-11-09 19:00 ` Andrew Morton
2018-11-09 19:16 ` Vlastimil Babka
2018-11-09 19:47 ` Darryl T. Agostinelli
2018-11-09 21:31 ` Vlastimil Babka
2018-11-12 9:55 ` David Laight
2018-11-13 18:22 ` Vlastimil Babka
2018-11-21 13:22 ` Vlastimil Babka
2018-11-19 11:04 ` Pavel Machek
2018-11-19 12:51 ` Vlastimil Babka
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1541526521.196084.184.camel@acm.org \
--to=bvanassche@acm.org \
--cc=akpm@linux-foundation.org \
--cc=alexander.duyck@gmail.com \
--cc=cl@linux.com \
--cc=guro@fb.com \
--cc=iamjoonsoo.kim@lge.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux@rasmusvillemoes.dk \
--cc=mgorman@techsingularity.net \
--cc=penberg@kernel.org \
--cc=rientjes@google.com \
--cc=vbabka@suse.cz \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).