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

[Krzysztof Kozlowski]

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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