thp: do_huge_pmd_wp_page(): handle huge zero page

On write access to huge zero page we alloc a new huge page and clear it.

If ENOMEM, graceful fallback: we create a new pmd table and set pte around
fault address to newly allocated normal (4k) page.  All other ptes in the
pmd set to normal zero page.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 4af4f0b1be4cad5cf231d565f5116745aa969a35..4b80bad4a367630e6126ade2c7ae3e51b7a36368 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -516,6 +516,14 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
 }
 #endif
 
+#ifndef my_zero_pfn
+static inline unsigned long my_zero_pfn(unsigned long addr)
+{
+       extern unsigned long zero_pfn;
+       return zero_pfn;
+}
+#endif
+
 /*
  * Multiple processes may "see" the same page. E.g. for untouched
  * mappings of /dev/null, all processes see the same page full of

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 650625390f616ddb1a17e8e072bd76476e675199..a959b3a4ddd5471dc2e73609917bfa7acd0fc705 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -858,6 +858,70 @@ unlock:
        spin_unlock(&mm->page_table_lock);
 }
 
+static int do_huge_pmd_wp_zero_page_fallback(struct mm_struct *mm,
+               struct vm_area_struct *vma, unsigned long address,
+               pmd_t *pmd, unsigned long haddr)
+{
+       pgtable_t pgtable;
+       pmd_t _pmd;
+       struct page *page;
+       int i, ret = 0;
+       unsigned long mmun_start;       /* For mmu_notifiers */
+       unsigned long mmun_end;         /* For mmu_notifiers */
+
+       page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
+       if (!page) {
+               ret |= VM_FAULT_OOM;
+               goto out;
+       }
+
+       if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) {
+               put_page(page);
+               ret |= VM_FAULT_OOM;
+               goto out;
+       }
+
+       clear_user_highpage(page, address);
+       __SetPageUptodate(page);
+
+       mmun_start = haddr;
+       mmun_end   = haddr + HPAGE_PMD_SIZE;
+       mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
+
+       spin_lock(&mm->page_table_lock);
+       pmdp_clear_flush(vma, haddr, pmd);
+       /* leave pmd empty until pte is filled */
+
+       pgtable = pgtable_trans_huge_withdraw(mm);
+       pmd_populate(mm, &_pmd, pgtable);
+
+       for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
+               pte_t *pte, entry;
+               if (haddr == (address & PAGE_MASK)) {
+                       entry = mk_pte(page, vma->vm_page_prot);
+                       entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+                       page_add_new_anon_rmap(page, vma, haddr);
+               } else {
+                       entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
+                       entry = pte_mkspecial(entry);
+               }
+               pte = pte_offset_map(&_pmd, haddr);
+               VM_BUG_ON(!pte_none(*pte));
+               set_pte_at(mm, haddr, pte, entry);
+               pte_unmap(pte);
+       }
+       smp_wmb(); /* make pte visible before pmd */
+       pmd_populate(mm, pmd, pgtable);
+       spin_unlock(&mm->page_table_lock);
+       inc_mm_counter(mm, MM_ANONPAGES);
+
+       mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+
+       ret |= VM_FAULT_WRITE;
+out:
+       return ret;
+}
+
 static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
                                        struct vm_area_struct *vma,
                                        unsigned long address,
@@ -964,19 +1028,21 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
                        unsigned long address, pmd_t *pmd, pmd_t orig_pmd)
 {
        int ret = 0;
-       struct page *page, *new_page;
+       struct page *page = NULL, *new_page;
        unsigned long haddr;
        unsigned long mmun_start;       /* For mmu_notifiers */
        unsigned long mmun_end;         /* For mmu_notifiers */
 
        VM_BUG_ON(!vma->anon_vma);
+       haddr = address & HPAGE_PMD_MASK;
+       if (is_huge_zero_pmd(orig_pmd))
+               goto alloc;
        spin_lock(&mm->page_table_lock);
        if (unlikely(!pmd_same(*pmd, orig_pmd)))
                goto out_unlock;
 
        page = pmd_page(orig_pmd);
        VM_BUG_ON(!PageCompound(page) || !PageHead(page));
-       haddr = address & HPAGE_PMD_MASK;
        if (page_mapcount(page) == 1) {
                pmd_t entry;
                entry = pmd_mkyoung(orig_pmd);
@@ -988,7 +1054,7 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
        }
        get_page(page);
        spin_unlock(&mm->page_table_lock);
-
+alloc:
        if (transparent_hugepage_enabled(vma) &&
            !transparent_hugepage_debug_cow())
                new_page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
@@ -998,24 +1064,34 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
 
        if (unlikely(!new_page)) {
                count_vm_event(THP_FAULT_FALLBACK);
-               ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
-                                                  pmd, orig_pmd, page, haddr);
-               if (ret & VM_FAULT_OOM)
-                       split_huge_page(page);
-               put_page(page);
+               if (is_huge_zero_pmd(orig_pmd)) {
+                       ret = do_huge_pmd_wp_zero_page_fallback(mm, vma,
+                                       address, pmd, haddr);
+               } else {
+                       ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
+                                       pmd, orig_pmd, page, haddr);
+                       if (ret & VM_FAULT_OOM)
+                               split_huge_page(page);
+                       put_page(page);
+               }
                goto out;
        }
        count_vm_event(THP_FAULT_ALLOC);
 
        if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))) {
                put_page(new_page);
-               split_huge_page(page);
-               put_page(page);
+               if (page) {
+                       split_huge_page(page);
+                       put_page(page);
+               }
                ret |= VM_FAULT_OOM;
                goto out;
        }
 
-       copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
+       if (is_huge_zero_pmd(orig_pmd))
+               clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
+       else
+               copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
        __SetPageUptodate(new_page);
 
        mmun_start = haddr;
@@ -1023,7 +1099,8 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
        mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 
        spin_lock(&mm->page_table_lock);
-       put_page(page);
+       if (page)
+               put_page(page);
        if (unlikely(!pmd_same(*pmd, orig_pmd))) {
                spin_unlock(&mm->page_table_lock);
                mem_cgroup_uncharge_page(new_page);
@@ -1031,14 +1108,18 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
                goto out_mn;
        } else {
                pmd_t entry;
-               VM_BUG_ON(!PageHead(page));
                entry = mk_huge_pmd(new_page, vma);
                pmdp_clear_flush(vma, haddr, pmd);
                page_add_new_anon_rmap(new_page, vma, haddr);
                set_pmd_at(mm, haddr, pmd, entry);
                update_mmu_cache_pmd(vma, address, pmd);
-               page_remove_rmap(page);
-               put_page(page);
+               if (is_huge_zero_pmd(orig_pmd))
+                       add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
+               else {
+                       VM_BUG_ON(!PageHead(page));
+                       page_remove_rmap(page);
+                       put_page(page);
+               }
                ret |= VM_FAULT_WRITE;
        }
        spin_unlock(&mm->page_table_lock);

diff --git a/mm/memory.c b/mm/memory.c
index 765377385632086e872058cb46fe7958dadd472f..259b34fe1347632bf3ada80fd589730fca5e132f 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -724,13 +724,6 @@ static inline int is_zero_pfn(unsigned long pfn)
 }
 #endif
 
-#ifndef my_zero_pfn
-static inline unsigned long my_zero_pfn(unsigned long addr)
-{
-       return zero_pfn;
-}
-#endif
-
 /*
  * vm_normal_page -- This function gets the "struct page" associated with a pte.
  *