linux-kernel - Re: [PATCH v3 03/16] slab: Ignore the cflgs bit in cache creation

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Date:	Tue, 18 Sep 2012 15:20:11 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Glauber Costa <glommer@...allels.com>
cc:	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	kamezawa.hiroyu@...fujitsu.com, devel@...nvz.org,
	Tejun Heo <tj@...nel.org>, linux-mm@...ck.org,
	Suleiman Souhlal <suleiman@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH v3 03/16] slab: Ignore the cflgs bit in cache creation

On Tue, 18 Sep 2012, Glauber Costa wrote:

> No cache should ever pass that as a creation flag, since this bit is
> used to mark an internal decision of the slab about object placement. We
> can just ignore this bit if it happens to be passed (such as when
> duplicating a cache in the kmem memcg patches)

If we do this then I would like to see a general masking of internal
allocator bits in kmem_cache_create. We could declare the highest byte to
be the internal slab flags. SLUB uses two flags in that area. SLAB uses
one.

F.e. add

#define SLAB_INTERNAL 0xFF00000000UL

to slab.h.

Then the flags can then be masked in mm/slab_common.c

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