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

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Message-ID: <20190925220357.GA162930@google.com>
Date:   Wed, 25 Sep 2019 16:03:57 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        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>,
        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
Subject: Re: [PATCH v3 4/4] mm: remove unnecessary smp_wmb() in
 __SetPageUptodate()

On Tue, Sep 24, 2019 at 04:50:36PM -0700, Matthew Wilcox wrote:
> On Tue, Sep 24, 2019 at 05:24:59PM -0600, Yu Zhao wrote:
> > +/*
> > + * Only use this function when there is a following write barrier, e.g.,
> > + * an explicit smp_wmb() and/or the page will be added to page or swap
> > + * cache locked.
> > + */
> >  static __always_inline void __SetPageUptodate(struct page *page)
> >  {
> >  	VM_BUG_ON_PAGE(PageTail(page), page);
> > -	smp_wmb();
> >  	__set_bit(PG_uptodate, &page->flags);
> >  }
> 
> Isn't this now the same as __SETPAGEFLAG(uptodate, Uptodate, PF_NO_TAIL)?

Indeed. I'll use the macro in the next version.