linux-kernel - [PATCH v3 1/4] mm: remove unnecessary smp_wmb() in collapse_huge

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Message-Id: <20190924232459.214097-1-yuzhao@google.com>
Date:   Tue, 24 Sep 2019 17:24:56 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hughd@...gle.com>,
        "Jérôme Glisse" <jglisse@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Lance Roy <ldr709@...il.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Dave Airlie <airlied@...hat.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Souptick Joarder <jrdr.linux@...il.com>,
        Mel Gorman <mgorman@...e.de>, Jan Kara <jack@...e.cz>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Huang Ying <ying.huang@...el.com>,
        Aaron Lu <ziqian.lzq@...fin.com>,
        Omar Sandoval <osandov@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vineeth Remanan Pillai <vpillai@...italocean.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Pavel Tatashin <pavel.tatashin@...rosoft.com>,
        David Hildenbrand <david@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Anthony Yznaga <anthony.yznaga@...cle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Yu Zhao <yuzhao@...gle.com>
Subject: [PATCH v3 1/4] mm: remove unnecessary smp_wmb() in collapse_huge_page()

__SetPageUptodate() always has a built-in smp_wmb() to make sure
user data copied to a new page appears before set_pmd_at().

Signed-off-by: Yu Zhao <yuzhao@...gle.com>
---
 mm/khugepaged.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index ccede2425c3f..70ff98e1414d 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1067,13 +1067,6 @@ static void collapse_huge_page(struct mm_struct *mm,
 	_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);
-- 
2.23.0.351.gc4317032e6-goog