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

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Message-ID: <alpine.DEB.2.00.1209261810180.7072@chino.kir.corp.google.com>
Date:	Wed, 26 Sep 2012 18:12:30 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Christoph Lameter <cl@...ux.com>
cc:	Glauber Costa <glommer@...allels.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 Wed, 26 Sep 2012, Christoph Lameter wrote:

> > Nack, this is already handled by CREATE_MASK in the mm/slab.c allocator;
> 
> CREATE_MASK defines legal flags that can be specified. Other flags cause
> and error. This is about flags that are internal that should be ignored
> when specified.
> 

That should be ignored for the mm/slab.c allocator, yes.

> I think it makes sense to reserve some top flags for internal purposes.
> 

It depends on the implementation: if another slab allocator were to use 
additional bits that would be a no-op with mm/slab.c, then this patch 
would be too restrictive.  There's also no requirement that any "internal 
flags" reserved by a slab allocator implementation must be shared in the 
same kmem_cache field as the flags passed to kmem_cache_create() -- it's 
actually better if they aren't since they seldom need to be accessed in 
the same cacheline.
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