linux-kernel - RE: [PATCH v2 1/8] minmax: Put all the clamp() definitions together

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Message-ID: <b47fad1d0cf8449886ad148f8c013dae@AcuMS.aculab.com>
Date: Sun, 28 Jul 2024 18:11:18 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Linus Torvalds' <torvalds@...uxfoundation.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Jens Axboe
	<axboe@...nel.dk>, "Matthew Wilcox (Oracle)" <willy@...radead.org>,
	"Christoph Hellwig" <hch@...radead.org>, Andrew Morton
	<akpm@...ux-foundation.org>, "Andy Shevchenko"
	<andriy.shevchenko@...ux.intel.com>, Dan Carpenter
	<dan.carpenter@...aro.org>, Arnd Bergmann <arnd@...nel.org>,
	"Jason@...c4.com" <Jason@...c4.com>, "pedro.falcato@...il.com"
	<pedro.falcato@...il.com>, Mateusz Guzik <mjguzik@...il.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, Lorenzo Stoakes
	<lorenzo.stoakes@...cle.com>
Subject: RE: [PATCH v2 1/8] minmax: Put all the clamp() definitions together

From: Linus Torvalds
> Sent: 28 July 2024 18:25
> 
> On Sun, 28 Jul 2024 at 07:18, David Laight <David.Laight@...lab.com> wrote:
> >
> > +#define min_t(type, x, y)      __careful_cmp(min, (type)(x), (type)(y))
> > +#define max_t(type, x, y)      __careful_cmp(max, (type)(x), (type)(y))
> 
> This is unrelated to your patch, but since it moves things around and
> touches these, I reacted to it..
> 
> We should *not* use __careful_cmp() here.
> 
> Why? Because part of __careful_cmp() is the "only use arguments once".
> 
> But *another* part of __careful_cmp() is "be careful about the types"
> in __cmp_once().
> 
> And being careful about the types is what causes horrendous expansion,
> and is pointless when we just forced things to be the same type.
> 
> So we should split __careful_cmp() into one that does just the "do
> once" and one that then also does the type checking.
...

Yes I've seen that and left well alone :-)
Or rather, left it until after MIN() and MAX() are used for constants.

Although min_t(type,x,y) should just be
	type __x = x;
	type __y = y;
	__x < __y ? __x : __y;
Absolutely no point doing anything else.

	David

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