Re: 2.6.17-mm1

[mel@skynet.ie (Mel Gorman)]

On (23/06/06 17:06), Franck Bui-Huu didst pronounce:
> Mel Gorman wrote:
> > On (23/06/06 14:22), Franck Bui-Huu didst pronounce:
> >> Mel Gorman wrote:
> >>> On (22/06/06 19:25), Franck Bui-Huu didst pronounce:
> >>>>> I know, but what I'm getting at is that ARCH_PFN_OFFSET may be unnecessary
> >>>>> with flatmem-relax-requirement-for-memory-to-start-at-pfn-0.patch applied.
> >>>> yes it seems so. But ARCH_PFN_OFFSET has been used before your patch
> >>>> has been sent. So your patch seems to be incomplete...
> >>> Difficult to argue with that logic.
> >>>
> >> sorry, I was just meaning that ARCH_PFN_OFFSET had been introduced to
> >> solve this before your patch has been sent. So the requirement for
> >> memory to start at pfn 0 is already solved.
> >>
> > 
> > In that case, the patch is as simple as you suggested earlier (patch
> > below). The only downside is that we hold onto ARCH_PFN_OFFSET which is a
> > bit of an obscure #define if you ask me. The obscurity can be lived with of
> > course, but it'd be nice to kick away ARCH_PFN_OFFSET if possible.
> > 
> 
> what do you think about this use of ARCH_PFN_OFFSET ?
> 

I believe that arches calling free_area_init_node() directly, but using
CONFIG_FLAT_NODE_MEM_MAP will have problems with this. There is no
guarantee that pgdat->node_start_pfn will have any relation to
ARCH_PFN_OFFSET. It is why in an earlier patch, I made a check for
ARCH_PFN_OFFSET == pgdat->node_start_pfn and only then printed a message
saying that ARCH_PFN_OFFSET was unnecessary.

> diff --git a/mm/bootmem.c b/mm/bootmem.c
> index d213fed..fd28eed 100644
> --- a/mm/bootmem.c
> +++ b/mm/bootmem.c
> @@ -377,11 +377,11 @@ unsigned long __init free_all_bootmem_no
>  	return(free_all_bootmem_core(pgdat));
>  }
>  
> -unsigned long __init init_bootmem (unsigned long start, unsigned long pages)
> +unsigned long __init init_bootmem(unsigned long start, unsigned long pages)
>  {
>  	max_low_pfn = pages;
>  	min_low_pfn = start;
> -	return(init_bootmem_core(NODE_DATA(0), start, 0, pages));
> +	return init_bootmem_core(NODE_DATA(0), start, ARCH_PFN_OFFSET, pages);
>  }
>  
>  #ifndef CONFIG_HAVE_ARCH_BOOTMEM_NODE
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index ed6a40f..43abaeb 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2154,7 +2154,7 @@ #ifdef CONFIG_FLATMEM
>  		 * relative to node_mem_map to maintain this
>  		 * relationship.
>  		 */
> -		mem_map = map - ARCH_PFN_OFFSET;
> +		mem_map = map - pgdat->node_start_pfn;
>  #endif
>  #endif /* CONFIG_FLAT_NODE_MEM_MAP */
>  }
> @@ -2181,8 +2181,7 @@ #endif
>  
>  void __init free_area_init(unsigned long *zones_size)
>  {
> -	free_area_init_node(0, NODE_DATA(0), zones_size,
> -			__pa(PAGE_OFFSET) >> PAGE_SHIFT, NULL);
> +	free_area_init_node(0, NODE_DATA(0), zones_size, ARCH_PFN_OFFSET, NULL);
>  }
>  
>  #ifdef CONFIG_PROC_FS

-- 
-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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