linux-kernel - Re: [PATCH] f2fs: add unlikely() macro for compiler more aggressively

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Message-ID: <87siu5vnvk.fsf@tassilo.jf.intel.com>
Date:	Fri, 06 Dec 2013 10:24:31 -0800
From:	Andi Kleen <andi@...stfloor.org>
To:	Jaegeuk Kim <jaegeuk.kim@...sung.com>
Cc:	unlisted-recipients:; (no To-header on input)
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net,
	Chao Yu <chao2.yu@...sung.com>
Subject: Re: [PATCH] f2fs: add unlikely() macro for compiler more aggressively

Jaegeuk Kim <jaegeuk.kim@...sung.com> writes:
>  	struct page *page;
>  repeat:
>  	page = grab_cache_page(mapping, index);
> -	if (!page) {
> +	if (unlikely(!page)) {

This is completely pointless, gcc already considers any test for NULL
unlikely.

In general i would advise against splattering unlikely all over your
code, the benefits are very minimal and programers often get it wrong.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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