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SubjectRe: 2.6.15-rc4 panic in __nr_to_section() with CONFIG_SPARSEMEM
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On Wed, 2005-12-07 at 16:48 -0800, Dave Hansen wrote:
> On Wed, 2005-12-07 at 15:22 -0800, Badari Pulavarty wrote:
> > BTW, the problem seems to be while dealing with shared memory areas
> > that are backed by largepages.
>
> I think this is likely not directly a sparsemem problem. It probably
> just shows symptoms earlier.
>
> See the attached patch. It attempts to detect and handle hugetlb pages
> in the smaps code. However, I think one of the root issues here is that
> bad_pmd() triggers for hugetlb pmds. I audited a few places where it is
> called, and at least a couple of them can't have hugepages handed into
> them, like fork().
>
> -- Dave
>
>
>
> ---
>
> proc-dups-dave/fs/proc/task_mmu.c | 22 ++++++++++++++++++++++
> 1 files changed, 22 insertions(+)
>
> 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 2005-12-07 16:34:47.000000000 -0800
> @@ -245,6 +245,28 @@ static inline void smaps_pmd_range(struc
> pmd = pmd_offset(pud, addr);
> do {
> next = pmd_addr_end(addr, end);
> +
> + if (pmd_huge(*pmd)) {
> + struct page *page;
> +
> + page = follow_huge_pmd(vma->vm_mm, addr, pmd, 0);
> + if (!page)
> + continue;
> +
> + mss->resident += HPAGE_SIZE;
> + if (page_count(page) >= 2) {
> + if (pte_dirty(*(pte_t *)pmd))
> + mss->shared_dirty += HPAGE_SIZE;
> + else
> + mss->shared_clean += HPAGE_SIZE;
> + } else {
> + if (pte_dirty(*(pte_t *)pmd))
> + mss->private_dirty += HPAGE_SIZE;
> + else
> + mss->private_clean += HPAGE_SIZE;
> + }
> + continue;
> + }
> if (pmd_none_or_clear_bad(pmd))
> continue;
> smaps_pte_range(vma, pmd, addr, next, mss);


No. It doesn't help. It looks like ppc pmd_huge() always returns 0.
Don't know why ? :(

Thanks,
Badari

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