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SubjectRe: [PATCH 2/2] [BUGFIX] pagemap: fix pfn calculation for hugepage
On Fri, 19 Mar 2010 16:27:32 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> On Fri, 19 Mar 2010 16:10:23 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>
> > On Fri, 19 Mar 2010 15:26:36 +0900
> > Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> wrote:
> >
> > > When we look into pagemap using page-types with option -p, the value
> > > of pfn for hugepages looks wrong (see below.)
> > > This is because pte was evaluated only once for one vma
> > > although it should be updated for each hugepage. This patch fixes it.
> > >
> > > $ page-types -p 3277 -Nl -b huge
> > > voffset offset len flags
> > > 7f21e8a00 11e400 1 ___U___________H_G________________
> > > 7f21e8a01 11e401 1ff ________________TG________________
> > > 7f21e8c00 11e400 1 ___U___________H_G________________
> > > 7f21e8c01 11e401 1ff ________________TG________________
> > > ^^^
> > > should not be the same
> > >
> > > With this patch applied:
> > >
> > > $ page-types -p 3386 -Nl -b huge
> > > voffset offset len flags
> > > 7fec7a600 112c00 1 ___UD__________H_G________________
> > > 7fec7a601 112c01 1ff ________________TG________________
> > > 7fec7a800 113200 1 ___UD__________H_G________________
> > > 7fec7a801 113201 1ff ________________TG________________
> > > ^^^
> > > OK
> > >
> > Hmm. Is this bug ? To me, it's just shown in hugepage's pagesize, by design.
> >
> I'm sorry it seems this is bugfix.
>
> But, this means hugeltb_entry() is not called per hugetlb entry...isn't it ?
>
> Why hugetlb_entry() cannot be called per hugeltb entry ? Don't we need a code
> for a case as pmd_size != hugetlb_size in walk_page_range() for generic fix ?
>

How about this style ? This is an idea-level patch. not tested at all.
(I have no test enviroment for multiple hugepage size.)

feel free to reuse fragments from this patch.
==

Not-tested-at-all!!

Now, walk_page_range() support page-table-walk on hugetlb.
But, it assumes that hugepage-size == pmd_size and hugetlb callback
is called per pmd not per pte of hugepage.

In some arch (ia64), hugepage-size is not pmd size (by config.)

This patch modifies hugetlb callback is called per hugetlb-ptes.

---
mm/pagewalk.c | 81 +++++++++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 67 insertions(+), 14 deletions(-)

Index: mmotm-2.6.34-Mar11/mm/pagewalk.c
===================================================================
--- mmotm-2.6.34-Mar11.orig/mm/pagewalk.c
+++ mmotm-2.6.34-Mar11/mm/pagewalk.c
@@ -79,7 +79,65 @@ static int walk_pud_range(pgd_t *pgd, un

return err;
}
+#ifdef CONFIG_HUGELB_PAGE
+static unsigned long
+__hugepage_next_offset(struct vm_area_struct *vma,
+ unsigned long addr, unsigned long end)
+{
+ struct hstate *hs = hstate_vma(vma);
+ unsigned long size = huge_page_size(hs);
+ unsigned long base = addr & huge_page_mask(hs);
+ unsigned long limit;
+ /* Hugepage is very tighty coupled with vma. */
+ if (end > vma->end)
+ limit = vma->end;
+ else
+ limit = end;
+
+ if (base + size < limit)
+ return base + size;
+ return limit;
+}

+static int walk_hugepage_range(struct mm_struct *mm, struct vm_area_struct *vma,
+ unsigned long addr, unsigned long end)
+{
+ pte_t *pte;
+ struct hstate *hs = hstate_vma(vma);
+ unsigned long size = huge_page_size(hs);
+
+ /*
+ * [addr...end) is guaranteeed to be under a vma
+ * (see __hugepage_next_offset())
+ */
+
+ hs = hstate_vma(vma);
+ do {
+ pte = huge_pte_offset(walk->mm, addr & huge_page_mask(hs));
+ next = (addr & huge_page_mask(hs)) + size;
+ if (next > end)
+ next = end;
+ if (pte && !huge_pte_none(huge_ptep_get(pte))
+ && walk->hugetlb_entry)
+ err = walk->hugetlb_entry(pte, addr, next, walk);
+ } while (addr = next, addr != end);
+
+ return err;
+}
+#else
+static unsigned long
+__hugepage_next_offset(struct vm_area_struct *vma,
+ unsigned long addr, unsigned long end)
+{
+ BUG();
+ return 0;
+}
+static int walk_hugepage_range(struct mm_struct *mm,
+ struct vm_area_struct *vma, unsigned long addr, unsigned long end)
+{
+ return 0;
+}
+#endif
/**
* walk_page_range - walk a memory map's page tables with a callback
* @mm: memory map to walk
@@ -126,25 +184,20 @@ int walk_page_range(unsigned long addr,
* we can't handled it in the same manner as non-huge pages.
*/
vma = find_vma(walk->mm, addr);
-#ifdef CONFIG_HUGETLB_PAGE
- if (vma && is_vm_hugetlb_page(vma)) {
- pte_t *pte;
- struct hstate *hs;

- if (vma->vm_end < next)
- next = vma->vm_end;
- hs = hstate_vma(vma);
- pte = huge_pte_offset(walk->mm,
- addr & huge_page_mask(hs));
- if (pte && !huge_pte_none(huge_ptep_get(pte))
- && walk->hugetlb_entry)
- err = walk->hugetlb_entry(pte, addr,
- next, walk);
+ if (vma && is_vm_hugetlb_page(vma)) {
+ /*
+ * In many archs, hugepage-size fits pmd size. But in
+ * some arch, we cannot assume that.
+ */
+ next = __hugepage_next_offset(vma, addr, end);
+ err = walk_hugepage_range(walk->mm, vma, addr, next);
if (err)
break;
+ /* We don't know next's pgd == pgd+1 */
+ pgd = pgd_offset(walk->mm, next);
continue;
}
-#endif
if (pgd_none_or_clear_bad(pgd)) {
if (walk->pte_hole)
err = walk->pte_hole(addr, next, walk);





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