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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id c142si6153531pfb.33.2019.02.15.10.08.55 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 15 Feb 2019 10:08:55 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=N6vgbDuA; spf=pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=willy@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=ekIKuh6zBnupKG9gxO673zuIE5kCUp3UX8vSRNljvIk=; b=N6vgbDuAO0pFZp1PJU1ZeiFyA ytwPOqX5TusjyRZIce5OHcQYYs3JVVuTD5LuzVjB4CxjutjoKS4NZs9QFgUcKdXLB7gtJ1URorkMb TNstdGaGILxTXQmo0Qr0PM6yGl/H/UEiXQxcDH+CVG23ZcxIbzqjiNePIi44h8UtgBQ188zYyyTSV eFkDmiks78XQrfwzlTAk8egXMa9LlLeD9OzBkE5gSLkbtTTuPKq5G4cuAiWId9oCv28UJWxRVMkFQ C+2kwPtXa2mhF1XtTTcUxzUY1N0PthxEuqk6mq99jR2F3ASJNSYoge3Y5zgoFsHyC+XCkvgPfRZEr and9h+huQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1guhuu-0003J4-NB; Fri, 15 Feb 2019 18:08:52 +0000 Date: Fri, 15 Feb 2019 10:08:52 -0800 From: Matthew Wilcox To: Christopher Lameter Cc: Dave Chinner , Jerome Glisse , Jason Gunthorpe , Dan Williams , Jan Kara , Doug Ledford , Ira Weiny , lsf-pc@lists.linux-foundation.org, linux-rdma , Linux MM , Linux Kernel Mailing List , John Hubbard , Michal Hocko Subject: Re: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA Message-ID: <20190215180852.GJ12668@bombadil.infradead.org> References: <20190208111028.GD6353@quack2.suse.cz> <20190211102402.GF19029@quack2.suse.cz> <20190211180654.GB24692@ziepe.ca> <20190214202622.GB3420@redhat.com> <20190214205049.GC12668@bombadil.infradead.org> <20190214213922.GD3420@redhat.com> <20190215011921.GS20493@dastard> <01000168f1d25e3a-2857236c-a7cc-44b8-a5f3-f51c2cfe6ce4-000000@email.amazonses.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <01000168f1d25e3a-2857236c-a7cc-44b8-a5f3-f51c2cfe6ce4-000000@email.amazonses.com> User-Agent: Mutt/1.9.2 (2017-12-15) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Feb 15, 2019 at 03:42:02PM +0000, Christopher Lameter wrote: > On Fri, 15 Feb 2019, Dave Chinner wrote: > > > Which tells us filesystem people that the applications are doing > > something that _will_ cause data corruption and hence not to spend > > any time triaging data corruption reports because it's not a > > filesystem bug that caused it. > > > > See open(2): > > > > Applications should avoid mixing O_DIRECT and normal I/O to > > the same file, and especially to overlapping byte regions in > > the same file. Even when the filesystem correctly handles > > the coherency issues in this situation, overall I/O > > throughput is likely to be slower than using either mode > > alone. Likewise, applications should avoid mixing mmap(2) > > of files with direct I/O to the same files. > > Since RDMA is something similar: Can we say that a file that is used for > RDMA should not use the page cache? That makes no sense. The page cache is the standard synchronisation point for filesystems and processes. The only problems come in for the things which bypass the page cache like O_DIRECT and DAX.