Re: [PATCH next] powerpc/mm: fix _PAGE_PTE breaking swapoff
From: Aneesh Kumar K.V <hidden>
Date: 2016-01-11 04:56:24
Also in:
linux-mm
Hugh Dickins [off-list ref] writes:
Swapoff after swapping hangs on the G5. That's because the _PAGE_PTE bit, added by set_pte_at(), is not expected by swapoff: so swap ptes cannot be recognized. I'm not sure whether a swap pte should or should not have _PAGE_PTE set: this patch assumes not, and fixes set_pte_at() to set _PAGE_PTE only on present entries.
One of the reason we added _PAGE_PTE is to enable HUGETLB migration. So we want migratio ptes to have _PAGE_PTE set.
But if that's wrong, a reasonable alternative would be to
#define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val(pte) & ~_PAGE_PTE })
#define __swp_entry_to_pte(x) __pte((x).val | _PAGE_PTE)We do clear _PAGE_PTE bits, when converting swp_entry_t to type and offset. Can you share the stack trace for the hang, which will help me understand this more ? .
quoted hunk ↗ jump to hunk
Signed-off-by: Hugh Dickins <hughd@google.com> --- arch/powerpc/mm/pgtable.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)--- 4.4-next/arch/powerpc/mm/pgtable.c 2016-01-06 11:54:01.477512251 -0800 +++ linux/arch/powerpc/mm/pgtable.c 2016-01-09 13:51:15.793485717 -0800@@ -180,9 +180,10 @@ void set_pte_at(struct mm_struct *mm, un VM_WARN_ON((pte_val(*ptep) & (_PAGE_PRESENT | _PAGE_USER)) == (_PAGE_PRESENT | _PAGE_USER)); /* - * Add the pte bit when tryint set a pte + * Add the pte bit when setting a pte (not a swap entry) */ - pte = __pte(pte_val(pte) | _PAGE_PTE); + if (pte_val(pte) & _PAGE_PRESENT) + pte = __pte(pte_val(pte) | _PAGE_PTE); /* Note: mm->context.id might not yet have been assigned as * this context might not have been activated yet when this
-aneesh