thp-copy_huge_pmd-copy-huge-zero-page-v6

It's easy to copy huge zero page. Just set destination pmd to huge zero
page.

It's safe to copy huge zero page since we have none yet :-p

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>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index afe8b3d034e212150b4f1dad3ee9c7f67ec7569f..662ac5bea124602307d1a2f0a744c73677146e57 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -958,6 +958,11 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
                pte_free(dst_mm, pgtable);
                goto out_unlock;
        }
+       /*
+        * mm->pagetable lock is enough to be sure that huge zero pmd is not
+        * under splitting since we don't split the page itself, only pmd to
+        * a page table.
+        */
        if (is_huge_zero_pmd(pmd)) {
                set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd);
                ret = 0;