Re: [PATCH v3 4/4] mm: remove unnecessary smp_wmb() in __SetPageUptodate()

From: Yu Zhao <yuzhao@google.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
	"Michal Hocko" <mhocko@suse.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
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	"Alexander Shishkin" <alexander.shishkin@linux.intel.com>,
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	"Namhyung Kim" <namhyung@kernel.org>,
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	"Jérôme Glisse" <jglisse@redhat.com>,
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	"Darrick J . Wong" <darrick.wong@oracle.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v3 4/4] mm: remove unnecessary smp_wmb() in __SetPageUptodate()
Date: Wed, 25 Sep 2019 16:03:57 -0600	[thread overview]
Message-ID: <20190925220357.GA162930@google.com> (raw)
In-Reply-To: <20190924235036.GA24516@bombadil.infradead.org>

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.