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Date: Mon, 12 Dec 2005 10:06:58 +0100
From: Eric Dumazet <dada1@cosmosbay.com>
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To: Nick Piggin <nickpiggin@yahoo.com.au>
CC: Paul Jackson <pj@sgi.com>, akpm@osdl.org, linux-kernel@vger.kernel.org,
       Simon Derr <Simon.Derr@bull.net>, Andi Kleen <ak@suse.de>,
       Christoph Lameter <clameter@sgi.com>
Subject: Re: [PATCH] Cpuset: rcu optimization of page alloc hook
References: <20051211233130.18000.2748.sendpatchset@jackhammer.engr.sgi.com> <439D39A8.1020806@cosmosbay.com> <439D3AD5.3080403@yahoo.com.au>
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Nick Piggin a écrit :
> Eric Dumazet wrote:
> 
>> Paul Jackson a écrit :
>>
>>> +
>>> +static kmem_cache_t *cpuset_cache;
>>> +
>>
>>
>>
>> Hi Paul
>>
>> Please do use __read_mostly for new kmem_cache :
>>
>> static kmem_cache_t *cpuset_cache __read_mostly;
>>
>> If not, the pointer can sit in the midle of a highly modified cache 
>> line, and multiple CPUS will have memory cache misses to access the 
>> cpuset_cache, while slab code/data layout itself is very NUMA/SMP 
>> friendly.
>>
> 
> Is it a good idea for all kmem_cache_t? If so, can we move
> __read_mostly to the type definition?
> 
> 

Well this question was already asked.

You cannot move __read_mostly to the type itself as some kmem_cache_t are 
included in some data structures.

struct {
  ...
  kmem_cache_t *slab;
  ...
};

And in this case you cannot automatically add __read_mostly

Eric