Message-ID: <439F2F39.3090800@cosmosbay.com>
Date: Tue, 13 Dec 2005 21:29:45 +0100
From: Eric Dumazet <dada1@cosmosbay.com>
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To: Paul Jackson <pj@sgi.com>
Cc: akpm@osdl.org, linux-kernel@vger.kernel.org, nickpiggin@yahoo.com.au,
       Simon.Derr@bull.net, ak@suse.de, clameter@sgi.com
Subject: Re: [PATCH] Cpuset: rcu optimization of page alloc hook
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Paul Jackson a ?crit :
> Detail question ...
> 
> Eric wrote:
> 
>>Say you move to read mostly most of struct kmem_cache *
> 
> 
> Does the following:
> 
> 	struct kmem_cache *cpuset_cache __read_mostly;
> 
> mark just the one word pointer 'cpuset_cache' as __read_mostly,
> or does it mark the whole dang cpuset cache?
> 
> I presume it just marks the one pointer word.  Am I wrong?

Only the pointer is placed onto read mostly section.

In fact the pointer is written once at boot time, then it is only read.

kmem_cache implementation is SMP/NUMA friendly, keeping care of false sharing 
issues, and node aware memory.

But the initial pointer *should* be in a cache line shared by all cpus to get 
best performance. It's easy to achive this since the pointer is only read. 
(well... mostly... )

> 
> I ask because the subtle phrasing of your comment reads to
> my ear as if you knew it marked the entire cache.  I can't
> tell if that is due to my ears having a different language
> accent than yours, or if it is due to my getting this wrong.
> 

Sorry...

Eric
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