khugepaged: reuse the smp_wmb() inside __SetPageUptodate()

smp_wmb() is needed to avoid the copy_huge_page writes to become visible
after the set_pmd_at() write here.  But we can reuse the smp_wmb() inside
__SetPageUptodate() to remove this redundant one.

Link: https://lkml.kernel.org/r/20210306032947.35921-3-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index d43812c..287e7ec 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1183,19 +1183,18 @@ static void collapse_huge_page(struct mm_struct *mm,
        __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl,
                        &compound_pagelist);
        pte_unmap(pte);
+       /*
+        * spin_lock() below is not the equivalent of smp_wmb(), but
+        * the smp_wmb() inside __SetPageUptodate() can be reused to
+        * avoid the copy_huge_page writes to become visible after
+        * the set_pmd_at() write.
+        */
        __SetPageUptodate(new_page);
        pgtable = pmd_pgtable(_pmd);
 
        _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
        _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
 
-       /*
-        * spin_lock() below is not the equivalent of smp_wmb(), so
-        * this is needed to avoid the copy_huge_page writes to become
-        * visible after the set_pmd_at() write.
-        */
-       smp_wmb();
-
        spin_lock(pmd_ptl);
        BUG_ON(!pmd_none(*pmd));
        page_add_new_anon_rmap(new_page, vma, address, true);