On Tue 17-05-16 15:32:46, Kirill A. Shutemov wrote: > Currently, faultaround code produces young pte. This can screw up vmscan > behaviour[1], as it makes vmscan think that these pages are hot and not > push them out on first round. > > Let modify faultaround to produce old pte, so they can easily be > reclaimed under memory pressure. Could you be more specific about what was the original issue that led to this patch? I can understand that marking all those pages new might be too optimistic but when does it matter actually? Sparsely access file mmap? > This can to some extend defeat purpose of faultaround on machines > without hardware accessed bit as it will not help up with reducing > number of minor page faults. > > We may want to disable faultaround on such machines altogether, but > that's subject for separate patchset. > > [1] https://lkml.kernel.org/r/1460992636-711-1-git-send-email-vinmenon@xxxxxxxxxxxxxx > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > Cc: Mel Gorman <mgorman@xxxxxxx> > Cc: Rik van Riel <riel@xxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > Cc: Vinayak Menon <vinmenon@xxxxxxxxxxxxxx> > Cc: Minchan Kim <minchan@xxxxxxxxxx> > --- > include/linux/mm.h | 2 +- > mm/filemap.c | 2 +- > mm/memory.c | 23 ++++++++++++++++++----- > 3 files changed, 20 insertions(+), 7 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 573dfebddcca..a0e773204be0 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -591,7 +591,7 @@ 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); > + struct page *page, pte_t *pte, bool write, bool anon, bool old); > #endif > > /* > diff --git a/mm/filemap.c b/mm/filemap.c > index b366a9902f1c..dd789e159a77 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2196,7 +2196,7 @@ 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); > + do_set_pte(vma, addr, page, pte, false, false, true); > unlock_page(page); > goto next; > unlock: > diff --git a/mm/memory.c b/mm/memory.c > index d79c6db41502..67c03b2fe20c 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2855,7 +2855,7 @@ 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) > + struct page *page, pte_t *pte, bool write, bool anon, bool old) > { > pte_t entry; > > @@ -2863,6 +2863,8 @@ 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); > @@ -3000,9 +3002,20 @@ 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); > - do_fault_around(vma, address, pte, pgoff, flags); > 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); > + goto unlock_out; > + } > pte_unmap_unlock(pte, ptl); > } > > @@ -3017,7 +3030,7 @@ 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); > + do_set_pte(vma, address, fault_page, pte, false, false, false); > unlock_page(fault_page); > unlock_out: > pte_unmap_unlock(pte, ptl); > @@ -3069,7 +3082,7 @@ 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); > + do_set_pte(vma, address, new_page, pte, true, true, false); > mem_cgroup_commit_charge(new_page, memcg, false, false); > lru_cache_add_active_or_unevictable(new_page, vma); > pte_unmap_unlock(pte, ptl); > @@ -3126,7 +3139,7 @@ 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); > + do_set_pte(vma, address, fault_page, pte, true, false, false); > pte_unmap_unlock(pte, ptl); > > if (set_page_dirty(fault_page)) > -- > 2.8.1 -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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