linux-kernel - Re: [PATCH 14/15] mm: Drop unlikely before IS_ERR(_OR

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Message-ID: <1438365622.19675.97.camel@perches.com>
Date:	Fri, 31 Jul 2015 11:00:22 -0700
From:	Joe Perches <joe@...ches.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	yalin wang <yalin.wang2010@...il.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linaro-kernel@...ts.linaro.org,
	open list <linux-kernel@...r.kernel.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	David Rientjes <rientjes@...gle.com>,
	Ebru Akagunduz <ebru.akagunduz@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	"open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
	Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 14/15] mm: Drop unlikely before IS_ERR(_OR_NULL)

On Fri, 2015-07-31 at 16:36 +0530, Viresh Kumar wrote:
> On 31-07-15, 03:28, Joe Perches wrote:
> > If it's all fixed, then it's unlikely to be needed in checkpatch.
> 
> I thought checkpatch is more about not committing new mistakes, rather than
> finding them in old code.

True, but checkpatch is more about style than substance.

There are a lot of things that _could_ be added to the script
but don't have to be because of relative rarity.

The unanswered fundamental though is whether the unlikely use
in #define IS_ERR_VALUE is useful.

include/linux/err.h:21:#define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO)

How often does using unlikely here make the code smaller/faster
with more recent compilers than gcc 3.4?  Or even using gcc 3.4.


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