Commit 9f8bdb3f authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds

mm: make swapoff more robust against soft dirty

Both s390 and powerpc have hit the issue of swapoff hanging, when
quite as x86_64 had them.  I think it would be much clearer if
HAVE_ARCH_SOFT_DIRTY was just a Kconfig option set by architectures to
determine whether the MEM_SOFT_DIRTY option should be offered, and the
actual code depend upon CONFIG_MEM_SOFT_DIRTY alone.

But won't embark on that change myself: instead make swapoff more
robust, by using pte_swp_clear_soft_dirty() on each pte it encounters,
without an explicit #ifdef CONFIG_MEM_SOFT_DIRTY.  That being a no-op,
whether the bit in question is defined as 0 or the asm-generic fallback
is used, unless soft dirty is fully turned on.

Why "maybe" in maybe_same_pte()? Rename it pte_same_as_swp().
Signed-off-by: default avatarHugh Dickins <>
Reviewed-by: default avatarAneesh Kumar K.V <>
Acked-by: default avatarCyrill Gorcunov <>
Cc: Laurent Dufour <>
Cc: Michael Ellerman <>
Cc: Martin Schwidefsky <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 88f306b6
......@@ -1111,19 +1111,9 @@ unsigned int count_swap_pages(int type, int free)
static inline int maybe_same_pte(pte_t pte, pte_t swp_pte)
static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte)
* When pte keeps soft dirty bit the pte generated
* from swap entry does not has it, still it's same
* pte from logical point of view.
pte_t swp_pte_dirty = pte_swp_mksoft_dirty(swp_pte);
return pte_same(pte, swp_pte) || pte_same(pte, swp_pte_dirty);
return pte_same(pte, swp_pte);
return pte_same(pte_swp_clear_soft_dirty(pte), swp_pte);
......@@ -1152,7 +1142,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
if (unlikely(!maybe_same_pte(*pte, swp_entry_to_pte(entry)))) {
if (unlikely(!pte_same_as_swp(*pte, swp_entry_to_pte(entry)))) {
mem_cgroup_cancel_charge(page, memcg, false);
ret = 0;
goto out;
......@@ -1210,7 +1200,7 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
* swapoff spends a _lot_ of time in this loop!
* Test inline before going to call unuse_pte.
if (unlikely(maybe_same_pte(*pte, swp_pte))) {
if (unlikely(pte_same_as_swp(*pte, swp_pte))) {
ret = unuse_pte(vma, pmd, addr, entry, page);
if (ret)
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