Hugh Dickins <hu...@google.com> writes:
> Both s390 and powerpc have hit the issue of swapoff hanging, when
> CONFIG_HAVE_ARCH_SOFT_DIRTY and CONFIG_MEM_SOFT_DIRTY ifdefs were
> not 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().
>
Ok this also explains, the _PAGE_PTE issue on powerpc you mentioned in the other
email.
Reviewed-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com>
> Signed-off-by: Hugh Dickins <hu...@google.com>
> ---
>
> mm/swapfile.c | 18 ++++--------------
> 1 file changed, 4 insertions(+), 14 deletions(-)
>
> --- 4.4-next/mm/swapfile.c 2016-01-06 11:54:46.327006983 -0800
> +++ linux/mm/swapfile.c 2016-01-09 13:39:19.632872694 -0800
> @@ -1109,19 +1109,9 @@ unsigned int count_swap_pages(int type,
> }
> #endif /* CONFIG_HIBERNATION */
>
> -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)
> {
> -#ifdef CONFIG_MEM_SOFT_DIRTY
> - /*
> - * 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);
> -#else
> - return pte_same(pte, swp_pte);
> -#endif
> + return pte_same(pte_swp_clear_soft_dirty(pte), swp_pte);
> }
>
> /*
> @@ -1150,7 +1140,7 @@ static int unuse_pte(struct vm_area_stru
> }
>
> 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;
> @@ -1208,7 +1198,7 @@ static int unuse_pte_range(struct vm_are
> * 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))) {
> pte_unmap(pte);
> ret = unuse_pte(vma, pmd, addr, entry, page);
> if (ret)
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