Message-id: <1375946794.25843.1.camel@AMDC1943>
Subject: Re: [RFC PATCH 3/4] mm: add zbud flag to page flags
From: Krzysztof Kozlowski <k.kozlowski@samsung.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Seth Jennings <sjenning@linux.vnet.ibm.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Kyungmin Park <kyungmin.park@samsung.com>
Date: Thu, 08 Aug 2013 09:26:34 +0200
In-reply-to: <52012B35.90801@intel.com>
References: <1375771361-8388-1-git-send-email-k.kozlowski@samsung.com>
 <1375771361-8388-4-git-send-email-k.kozlowski@samsung.com>
 <52012B35.90801@intel.com>
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Hi,

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.

How about using page->_mapcount with negative value (-129)? Just like
PageBuddy()?


Best regards,
Krzysztof

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