linux-kernel - Re: [PATCH] slab: Ignore internal flags in cache creation

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Date:	Fri, 28 Sep 2012 11:46:49 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	Christoph Lameter <cl@...ux.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, Michal Hocko <mhocko@...e.cz>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH] slab: Ignore internal flags in cache creation

On 09/28/2012 02:56 AM, David Rientjes wrote:
> On Thu, 27 Sep 2012, Glauber Costa wrote:
> 
>> But I still don't see the big reason for your objection. If other
>> allocator start using those bits, they would not be passed to
>> kmem_cache_alloc anyway, right? So what would be the big problem in
>> masking them out before it?
>>
> 
> A slab allocator implementation may allow for additional bits that are 
> currently not used or used for internal purposes by the current set of 
> slab allocators to be passed in the unsigned long to kmem_cache_create() 
> that would be a no-op on other allocators.  It's implementation defined, 
> so this masking should be done in the implementation, i.e. 
> __kmem_cache_create().
> 
> For context, as many people who attended the kernel summit and LinuxCon 
> are aware, a new slab allocator is going to be proposed soon that actually 
> uses additional bits that aren't defined for all slab allocators.  My 
> opinion is that leaving unused bits and reserved bits to the 
> implementation is the best software engineering practice.
> 

I am happy as long as we don't BUG and can mask out that feature.
If Christoph is happy with me masking it in the SLAB only, I'm also fine.
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