Re: Make show_mem() skip holes in a pgdat.

["Bob Picco" <bob.picco@hp.com>]

Robin Holt wrote:	[Thu Apr 13 2006, 09:14:42AM EDT]
> 
> This patch modifies ia64's show_mem() to walk the vmem_map page tables and
> rapidly skip forward across regions where the page tables are missing.
> This prevents the pfn_valid() check from causing numerous unnecessary
> page faults.
> 
> Without this patch on a 512 node 512 cpu system where every node has four
> memory holes, the show_mem() call takes 1 hour 18 minutes.  With this
> patch, it takes less than 3 seconds.
> 
> Signed-off-by: Robin Holt <holt@sgi.com>
> 
> ---
> Fixed.
> 
> 
> Index: linux-2.6/arch/ia64/mm/discontig.c
> =================================> --- linux-2.6.orig/arch/ia64/mm/discontig.c	2006-04-13 06:16:00.500029306 -0500
> +++ linux-2.6/arch/ia64/mm/discontig.c	2006-04-13 07:01:31.668069891 -0500
> @@ -519,6 +519,69 @@ void __cpuinit *per_cpu_init(void)
>  }
>  #endif /* CONFIG_SMP */
How about these changes to fix SPARSEMEM.
>  
> +
#ifdef CONFIG_VIRTUAL_MEM_MAP
> +static int find_next_valid_pfn_for_pgdat(pg_data_t *pgdat, int i)
> +{
> +	unsigned long end_address, hole_next_pfn;
> +	unsigned long stop_address;
> +
> +	end_address = (unsigned long) &vmem_map[pgdat->node_start_pfn + i];
> +	end_address = PAGE_ALIGN(end_address);
> +
> +	stop_address = (unsigned long) &vmem_map[
> +		pgdat->node_start_pfn + pgdat->node_spanned_pages];
> +
> +	do {
> +		pgd_t *pgd;
> +		pud_t *pud;
> +		pmd_t *pmd;
> +		pte_t *pte;
> +
> +		pgd = pgd_offset_k(end_address);
> +		if (pgd_none(*pgd)) {
> +			end_address += PTRS_PER_PUD *
> +				       PTRS_PER_PMD *
> +				       PTRS_PER_PTE *
> +				       PAGE_SIZE;
> +			continue;
> +		}
> +
> +		pud = pud_offset(pgd, end_address);
> +		if (pud_none(*pud)) {
> +			end_address += PTRS_PER_PMD *
> +				       PTRS_PER_PTE *
> +				       PAGE_SIZE;
> +			continue;
> +		}
> +
> +		pmd = pmd_offset(pud, end_address);
> +		if (pmd_none(*pmd)) {
> +			end_address += PTRS_PER_PTE *
> +				       PAGE_SIZE;
> +			continue;
> +		}
> +
> +		pte = pte_offset_kernel(pmd, end_address);
> +retry_pte:
> +		if (pte_none(*pte)) {
> +			end_address += PAGE_SIZE;
> +			pte++;
> +			if ((end_address < stop_address) &&
> +			    (end_address != ALIGN(end_address, 1UL << PMD_SHIFT)))
> +				goto retry_pte;
> +			continue;
> +		}
> +		/* Found next valid vmem_map page */
> +		break;
> +	} while (end_address < stop_address);
> +
> +	end_address = min(end_address, stop_address);
> +	end_address = end_address - (unsigned long) vmem_map + sizeof(struct page) - 1;
> +	hole_next_pfn = end_address / sizeof(struct page);
> +	return hole_next_pfn - pgdat->node_start_pfn;
> +}
#else
static inline int find_next_valid_pfn_for_pgdat(pg_data_t *pgdat, int i)
{
	return i + 1;
}
#endif
This should optimize out below for SPARSEMEM.

bob
> +
> +
>  /**
>   * show_mem - give short summary of memory stats
>   *
> @@ -547,8 +610,10 @@ void show_mem(void)
>  			struct page *page;
>  			if (pfn_valid(pgdat->node_start_pfn + i))
>  				page = pfn_to_page(pgdat->node_start_pfn + i);
> -			else
> +			else {
> +				i = find_next_valid_pfn_for_pgdat(pgdat, i) - 1;
>  				continue;
> +			}
>  			if (PageReserved(page))
>  				reserved++;
>  			else if (PageSwapCache(page))