linux-kernel - Re: [PATCH v6 19/29] memcg: infrastructure to match an allocation to the right cache

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Message-ID: <20121106080354.GA21167@dhcp22.suse.cz>
Date:	Tue, 6 Nov 2012 09:03:54 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Glauber Costa <glommer@...allels.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, kamezawa.hiroyu@...fujitsu.com,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Suleiman Souhlal <suleiman@...gle.com>,
	JoonSoo Kim <js1304@...il.com>, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v6 19/29] memcg: infrastructure to match an allocation to
 the right cache

On Mon 05-11-12 16:28:37, Andrew Morton wrote:
> On Thu,  1 Nov 2012 16:07:35 +0400
> Glauber Costa <glommer@...allels.com> wrote:
> 
> > +static __always_inline struct kmem_cache *
> > +memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp)
> 
> I still don't understand why this code uses __always_inline so much.

AFAIU, __always_inline (resp. __attribute__((always_inline))) is the
same thing as inline if optimizations are enabled
(http://ohse.de/uwe/articles/gcc-attributes.html#func-always_inline).
Which is the case for the kernel. I was always wondering why we have
this __always_inline thingy.
It has been introduced back in 2004 by Andi but the commit log doesn't
say much:
"
[PATCH] gcc-3.5 fixes
    
Trivial gcc-3.5 build fixes.
"
Andi what was the original motivation for this attribute?
 
> I don't recall seeing the compiler producing out-of-line versions of
> "static inline" functions

and if it decides then __always_inline will not help, right?

-- 
Michal Hocko
SUSE Labs
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