thp: zap_huge_pmd(): zap huge zero pmd

We don't have a mapped page to zap in huge zero page case.  Let's just clear
pmd and remove it from tlb.

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/mm/huge_memory.c b/mm/huge_memory.c
index 04eb489a6805330cc60297231194e09ef772ec9b..1ee34ddb46adc77b36e676eea28368eed3eef1b2 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1085,15 +1085,20 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
                pmd_t orig_pmd;
                pgtable = pgtable_trans_huge_withdraw(tlb->mm);
                orig_pmd = pmdp_get_and_clear(tlb->mm, addr, pmd);
-               page = pmd_page(orig_pmd);
                tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
-               page_remove_rmap(page);
-               VM_BUG_ON(page_mapcount(page) < 0);
-               add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
-               VM_BUG_ON(!PageHead(page));
-               tlb->mm->nr_ptes--;
-               spin_unlock(&tlb->mm->page_table_lock);
-               tlb_remove_page(tlb, page);
+               if (is_huge_zero_pmd(orig_pmd)) {
+                       tlb->mm->nr_ptes--;
+                       spin_unlock(&tlb->mm->page_table_lock);
+               } else {
+                       page = pmd_page(orig_pmd);
+                       page_remove_rmap(page);
+                       VM_BUG_ON(page_mapcount(page) < 0);
+                       add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
+                       VM_BUG_ON(!PageHead(page));
+                       tlb->mm->nr_ptes--;
+                       spin_unlock(&tlb->mm->page_table_lock);
+                       tlb_remove_page(tlb, page);
+               }
                pte_free(tlb->mm, pgtable);
                ret = 1;
        }