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

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Message-id: <1375859042.17079.1.camel@AMDC1943>
Date:	Wed, 07 Aug 2013 09:04:02 +0200
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Dave Hansen <dave.hansen@...el.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 wto, 2013-08-06 at 09:58 -0700, Dave Hansen wrote:
> 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.

Thanks for idea, I will try that.

Best regards,
Krzysztof


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