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

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Date:	Wed, 26 Sep 2012 14:57:21 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	David Rientjes <rientjes@...gle.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 Tue, 25 Sep 2012, David Rientjes 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.

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

> the flag extensions beyond those defined in the generic slab.h header are
> implementation defined.  It may be true that SLAB uses a bit only
> internally (and already protects it with a BUG_ON() in
> __kmem_cache_create()) but that doesn't mean other implementations can't
> use such a flag that would be a no-op on another allocator.

Other implementations such as SLUB also use the bits in that high range.

Simply ignoring the internal bits on cache creation if they are set is
IMHO not a bit issue and simplifies Glaubers task.

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