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>

1 files changed, 96 insertions, 15 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 650625390f61..a959b3a4ddd5 100644
--- 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);