From: Miaohe Lin <linmiaohe@xxxxxxxxxx> Subject: 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@xxxxxxxxxx Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx> Cc: Ebru Akagunduz <ebru.akagunduz@xxxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/khugepaged.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) --- a/mm/khugepaged.c~khugepaged-reuse-the-smp_wmb-inside-__setpageuptodate +++ a/mm/khugepaged.c @@ -1183,19 +1183,18 @@ static void collapse_huge_page(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); _
