linux-kernel - Re: [PATCH 1/5] linux/minmax.h: add non-atomic version of xchg

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Message-ID: <Y5OE3AX7DS/DfClX@smile.fi.intel.com>
Date:   Fri, 9 Dec 2022 20:56:28 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Andrzej Hajda <andrzej.hajda@...el.com>
Cc:     linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Andi Shyti <andi.shyti@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 1/5] linux/minmax.h: add non-atomic version of xchg

On Fri, Dec 09, 2022 at 04:48:39PM +0100, Andrzej Hajda wrote:
> The pattern of setting variable with new value and returning old
> one is very common in kernel. Usually atomicity of the operation
> is not required, so xchg seems to be suboptimal and confusing in
> such cases. Since name xchg is already in use and __xchg is used
> in architecture code, proposition is to name the macro exchange.
> 
> Signed-off-by: Andrzej Hajda <andrzej.hajda@...el.com>
> ---
> Hi,
> 
> I hope there will be place for such tiny helper in kernel.
> Quick cocci analyze shows there is probably few thousands places
> where it could be used, of course I do not intend to do it :).
> 
> I was not sure where to put this macro, I hope near swap definition
> is the most suitable place.

Ah, swap() in this context is not the same. minmax.h hosts it because
it's often related to the swap function in the sort-type algorithms.

> Moreover sorry if to/cc is not correct - get_maintainers.pl was
> more confused than me, to who address this patch.

...

>  include/linux/minmax.h | 14 ++++++++++++++

Does it really suit this header? I would expect something else.
Maybe include/linux/non-atomic/xchg.h, dunno.

Btw, have you looked if Ingo's gigantic series have done anything to cmpxchg.h
and related headers? Maybe some ideas can be taken from there?

-- 
With Best Regards,
Andy Shevchenko