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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 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);
_

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