Re: 2.6.15-rc4 panic in __nr_to_section() with CONFIG_SPARSEMEM

[Badari Pulavarty <pbadari@us.ibm.com>]

On Thu, 2005-12-08 at 16:16 -0800, Dave Hansen wrote:
> On Fri, 2005-12-09 at 10:48 +1100, David Gibson wrote:
> > On Thu, Dec 08, 2005 at 11:15:35AM -0800, Dave Hansen wrote:
> > > On Thu, 2005-12-08 at 08:07 -0800, Badari Pulavarty wrote:
> > > > No. It doesn't help. It looks like ppc pmd_huge() always returns 0.
> > > > Don't know why ? :(
> > > 
> > > The ppc64 hugetlb pages don't line up on PMD boundaries like they do on
> > > i386.  The entries are stored in regular old PTEs.  
> > > 
> > > I really don't like coding the two different hugetlb cases, but I can't
> > > think of a better way to do it.  Anyone care to test on ppc64?
> > 
> > > -		mss->resident += PAGE_SIZE;
> > > +		page_size = PAGE_SIZE;
> > > +		if (is_hugepage_only_range(vma->vm_mm, addr, end - addr))
> > > +			page_size = HPAGE_SIZE;
> > 
> > This is an incorrect usage of is_hugepage_only_range().  Although it
> > will get the right answer by accident here, that function should
> > *only* be used for testing whether a range is suitable for normal
> > pages, never for determining if hugepages are actually in use here.
> > You have the VMA here, so test its flag instead here.
> 
> Sounds good to me.  The flag should be faster to test as well.  Updated
> patch attached.  Shall I cook another one up to comment
> is_hugepage_only_range() so poor suckers like me don't make the mistake
> again?
> 
> -- Dave
> 
>  proc-dups-dave/fs/proc/task_mmu.c |   53 +++++++++++++++++++++++++++-----------
>  2 files changed, 39 insertions(+), 14 deletions(-)
> 
> diff -puN fs/proc/task_mmu.c~task_mmu_fix fs/proc/task_mmu.c
> --- proc-dups/fs/proc/task_mmu.c~task_mmu_fix	2005-12-07 16:34:38.000000000 -0800
> +++ proc-dups-dave/fs/proc/task_mmu.c	2005-12-08 16:13:55.000000000 -0800
> @@ -198,6 +198,24 @@ static int show_map(struct seq_file *m, 
>  	return show_map_internal(m, v, NULL);
>  }
>  
> +static void smaps_account_for_page(pte_t ptent, struct page *page,
> +					unsigned long page_size,
> +					struct mem_size_stats *mss)
> +{
> +	mss->resident += page_size;
> +	if (page_count(page) >= 2) {
> +		if (pte_dirty(ptent))
> +			mss->shared_dirty += page_size;
> +		else
> +			mss->shared_clean += page_size;
> +	} else {
> +		if (pte_dirty(ptent))
> +			mss->private_dirty += page_size;
> +		else
> +			mss->private_clean += page_size;
> +	}
> +}
> +
>  static void smaps_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
>  				unsigned long addr, unsigned long end,
>  				struct mem_size_stats *mss)
> @@ -205,32 +223,38 @@ static void smaps_pte_range(struct vm_ar
>  	pte_t *pte, ptent;
>  	spinlock_t *ptl;
>  	unsigned long pfn;
> +	unsigned long page_size;
>  	struct page *page;
>  
> +	if (pmd_huge(*pmd)) {
> +		struct page *page;
> +
> +		page = follow_huge_pmd(vma->vm_mm, addr, pmd, 0);
> +		if (!page)
> +			return;
> +
> +		ptent = *(pte_t *)pmd;
> +		smaps_account_for_page(ptent, page, HPAGE_SIZE, mss);
> +		return;
> +	}
>  	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
>  	do {
>  		ptent = *pte;
>  		if (!pte_present(ptent))
>  			continue;
>  
> -		mss->resident += PAGE_SIZE;
> +		page_size = PAGE_SIZE;
> +		if (is_vm_hugetlb_page(vma))
> +			page_size = HPAGE_SIZE;
> +
> +		mss->resident += page_size;
>  		pfn = pte_pfn(ptent);
>  		if (!pfn_valid(pfn))
>  			continue;
>  
>  		page = pfn_to_page(pfn);
> -		if (page_count(page) >= 2) {
> -			if (pte_dirty(ptent))
> -				mss->shared_dirty += PAGE_SIZE;
> -			else
> -				mss->shared_clean += PAGE_SIZE;
> -		} else {
> -			if (pte_dirty(ptent))
> -				mss->private_dirty += PAGE_SIZE;
> -			else
> -				mss->private_clean += PAGE_SIZE;
> -		}
> -	} while (pte++, addr += PAGE_SIZE, addr != end);
> +		smaps_account_for_page(ptent, page, page_size, mss);
> +	} while (pte++, addr += page_size, addr != end);
>  	pte_unmap_unlock(pte - 1, ptl);
>  	cond_resched();
>  }
> @@ -245,7 +269,8 @@ static inline void smaps_pmd_range(struc
>  	pmd = pmd_offset(pud, addr);
>  	do {
>  		next = pmd_addr_end(addr, end);
> -		if (pmd_none_or_clear_bad(pmd))
> +
> +		if (!pmd_huge(*pmd) && pmd_none_or_clear_bad(pmd))
>  			continue;
>  		smaps_pte_range(vma, pmd, addr, next, mss);
>  	} while (pmd++, addr = next, addr != end);
> diff -puN include/linux/hugetlb.h~task_mmu_fix include/linux/hugetlb.h
> _


NACK. 

Like I mentioned to you privately, I still get Oops with this patch for
largepages. Please let me know, if you have a new version to try.

Thanks,
Badari