linux-kernel - Re: [PATCH] ext4: use swap macro in mext_page_double

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Message-ID: <20180722221911.GC3358@thunk.org>
Date:   Sun, 22 Jul 2018 18:19:11 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ext4: use swap macro in mext_page_double_lock

On Mon, Jul 09, 2018 at 08:16:00AM -0500, Gustavo A. R. Silva wrote:
> Make use of the swap macro and remove unnecessary variable *tmp*.
> This makes the code easier to read and maintain. Also, reduces the
> stack usage.
> 
> This code was detected with the help of Coccinelle.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>

It doesn't actually reduce stack usage.  Look at the definition of
swap() in include/linux/kernel.h:

#define swap(a, b) \
	do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)

It removes the variable "tmp", and replace it with "__tmp".

It slightly reduces the number of lines of code, so it slightly makes
the code easier to maintainer.  But I think you are really
over-promising how much this commit helps.

Regards,

					- Ted