linux-kernel - Re: [RFC PATCH 3/4] mm: add zbud flag to page flags

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Message-ID: <52012B35.90801@intel.com>
Date:	Tue, 06 Aug 2013 09:58:29 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
CC:	Seth Jennings <sjenning@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>
Subject: Re: [RFC PATCH 3/4] mm: add zbud flag to page flags

On 08/05/2013 11:42 PM, Krzysztof Kozlowski wrote:
> +#ifdef CONFIG_ZBUD
> +	/* Allocated by zbud. Flag is necessary to find zbud pages to unuse
> +	 * during migration/compaction.
> +	 */
> +	PG_zbud,
> +#endif

Do you _really_ need an absolutely new, unshared page flag?
The zbud code doesn't really look like it uses any of the space in
'struct page'.

I think you could pretty easily alias PG_zbud=PG_slab, then use the
page->{private,slab_cache} (or some other unused field) in 'struct page'
to store a cookie to differentiate slab and zbud pages.
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