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SubjectRe: [PATCH 1/2] Revert "mm: make faultaround produce old ptes"
On Tue 14-06-16 11:42:29, Kirill A. Shutemov wrote:
> This reverts commit 5c0a85fad949212b3e059692deecdeed74ae7ec7.
>
> The commit causes ~6% regression in unixbench.

Is the regression fully explained? My understanding from the email
thread is that this is suspiciously too high. It is not like I would
be against the revert but having an explanation would be really
appreciated.

> Let's revert it for now and consider other solution for reclaim problem
> later.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Reported-by: "Huang, Ying" <ying.huang@intel.com>
> ---
> include/linux/mm.h | 2 +-
> mm/filemap.c | 2 +-
> mm/memory.c | 23 +++++------------------
> 3 files changed, 7 insertions(+), 20 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 5df5feb49575..ece042dfe23c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -602,7 +602,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
> }
>
> void do_set_pte(struct vm_area_struct *vma, unsigned long address,
> - struct page *page, pte_t *pte, bool write, bool anon, bool old);
> + struct page *page, pte_t *pte, bool write, bool anon);
> #endif
>
> /*
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 00ae878b2a38..20f3b1f33f0e 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2186,7 +2186,7 @@ repeat:
> if (file->f_ra.mmap_miss > 0)
> file->f_ra.mmap_miss--;
> addr = address + (page->index - vmf->pgoff) * PAGE_SIZE;
> - do_set_pte(vma, addr, page, pte, false, false, true);
> + do_set_pte(vma, addr, page, pte, false, false);
> unlock_page(page);
> goto next;
> unlock:
> diff --git a/mm/memory.c b/mm/memory.c
> index 15322b73636b..61fe7e7b56bf 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2877,7 +2877,7 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address,
> * vm_ops->map_pages.
> */
> void do_set_pte(struct vm_area_struct *vma, unsigned long address,
> - struct page *page, pte_t *pte, bool write, bool anon, bool old)
> + struct page *page, pte_t *pte, bool write, bool anon)
> {
> pte_t entry;
>
> @@ -2885,8 +2885,6 @@ void do_set_pte(struct vm_area_struct *vma, unsigned long address,
> entry = mk_pte(page, vma->vm_page_prot);
> if (write)
> entry = maybe_mkwrite(pte_mkdirty(entry), vma);
> - if (old)
> - entry = pte_mkold(entry);
> if (anon) {
> inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
> page_add_new_anon_rmap(page, vma, address, false);
> @@ -3032,20 +3030,9 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> */
> if (vma->vm_ops->map_pages && fault_around_bytes >> PAGE_SHIFT > 1) {
> pte = pte_offset_map_lock(mm, pmd, address, &ptl);
> - if (!pte_same(*pte, orig_pte))
> - goto unlock_out;
> do_fault_around(vma, address, pte, pgoff, flags);
> - /* Check if the fault is handled by faultaround */
> - if (!pte_same(*pte, orig_pte)) {
> - /*
> - * Faultaround produce old pte, but the pte we've
> - * handler fault for should be young.
> - */
> - pte_t entry = pte_mkyoung(*pte);
> - if (ptep_set_access_flags(vma, address, pte, entry, 0))
> - update_mmu_cache(vma, address, pte);
> + if (!pte_same(*pte, orig_pte))
> goto unlock_out;
> - }
> pte_unmap_unlock(pte, ptl);
> }
>
> @@ -3060,7 +3047,7 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> put_page(fault_page);
> return ret;
> }
> - do_set_pte(vma, address, fault_page, pte, false, false, false);
> + do_set_pte(vma, address, fault_page, pte, false, false);
> unlock_page(fault_page);
> unlock_out:
> pte_unmap_unlock(pte, ptl);
> @@ -3111,7 +3098,7 @@ static int do_cow_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> }
> goto uncharge_out;
> }
> - do_set_pte(vma, address, new_page, pte, true, true, false);
> + do_set_pte(vma, address, new_page, pte, true, true);
> mem_cgroup_commit_charge(new_page, memcg, false, false);
> lru_cache_add_active_or_unevictable(new_page, vma);
> pte_unmap_unlock(pte, ptl);
> @@ -3164,7 +3151,7 @@ static int do_shared_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> put_page(fault_page);
> return ret;
> }
> - do_set_pte(vma, address, fault_page, pte, true, false, false);
> + do_set_pte(vma, address, fault_page, pte, true, false);
> pte_unmap_unlock(pte, ptl);
>
> if (set_page_dirty(fault_page))
> --
> 2.8.1
>

--
Michal Hocko
SUSE Labs

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