Re: [PATCH] Get rid of zone_table V2

[Andrew Morton <akpm@osdl.org>]

On Sat, 30 Sep 2006 11:47:48 -0700 (PDT)
Christoph Lameter <clameter@sgi.com> wrote:

> There is still a problem after Andy's patch in connection with Optional 
> ZONE DMA that I pointed out earlier. If we only have a single zone then 
> ZONEID_PGSHIFT == 0. This is fine for the non NUMA case in which we have 
> only a single zone and ZONEID_MASK == 0 too. page_zone_id() will always be 
> 0.
> 
> In the NUMA case we still have one zone per node. Thus we need to have a 
> correct ZONEID_PGSHIFT in order to isolate the node number from page 
> flags. Right now we take NODES_SHIFT bits starting from 0!
> 
> I am not exactly sure how to fix that the right way given the complex
> nested macros. Andy may know.
> 
> The following patch checks for that condition. We can only allow 
> ZONEID_PGSHIFT to be zero if the ZONEID_MASK is also zero. (We cannot 
> check that with an #if because ZONEID_SHIFT contains a "sizeof(...)" 
> element)
> 
> Signed-off-by: Christoph Lameter <clameter@sgi.com>
> 
> Index: linux-2.6.18-mm2/include/linux/mm.h
> ===================================================================
> --- linux-2.6.18-mm2.orig/include/linux/mm.h	2006-09-30 13:22:27.732989275 -0500
> +++ linux-2.6.18-mm2/include/linux/mm.h	2006-09-30 13:23:06.604463587 -0500
> @@ -447,6 +447,7 @@ static inline enum zone_type page_zonenu
>   */
>  static inline int page_zone_id(struct page *page)
>  {
> +	BUG_ON(ZONEID_PGSHIFT == 0 && ZONEID_MASK);
>  	return (page->flags >> ZONEID_PGSHIFT) & ZONEID_MASK;
>  }
>  

BUILD_BUG_ON()?

What patch is this patch patching?  get-rid-of-zone_table.patch or one of
the ZONE_DMA-optionality ones?

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