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[54.240.9.37]) by mx.google.com with ESMTPS id o127si797402qkd.13.2019.02.15.10.31.37 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Fri, 15 Feb 2019 10:31:37 -0800 (PST) Received-SPF: pass (google.com: domain of 01000168f26d9e0c-aef3255a-5059-4657-b241-dae66663bbea-000000@amazonses.com designates 54.240.9.37 as permitted sender) client-ip=54.240.9.37; Authentication-Results: mx.google.com; dkim=pass header.i=@amazonses.com header.s=ug7nbtf4gccmlpwj322ax3p6ow6yfsug header.b="DW/4HFBW"; spf=pass (google.com: domain of 01000168f26d9e0c-aef3255a-5059-4657-b241-dae66663bbea-000000@amazonses.com designates 54.240.9.37 as permitted sender) smtp.mailfrom=01000168f26d9e0c-aef3255a-5059-4657-b241-dae66663bbea-000000@amazonses.com DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/simple; s=ug7nbtf4gccmlpwj322ax3p6ow6yfsug; d=amazonses.com; t=1550255496; h=Date:From:To:cc:Subject:In-Reply-To:Message-ID:References:MIME-Version:Content-Type:Feedback-ID; bh=FL49OqYV7AJ7BdfqMIiruaHQ/KIj/D+PCy38BhKpJ8M=; b=DW/4HFBWl7QxvxO7+RPK0EnTWciRC6KBevIyCX844sINXkFtro9foTj9NAy+yYNH KkrA17PnOuoFvHC503Pq6MYSRDKVdvWqqN3P0WOo5yW2T+28qcy/csPN+XvNkMyOgJ1 hDFPRkfFHIw71VRLb6JkcoK1iXbQB5k8exBjyM/I= Date: Fri, 15 Feb 2019 18:31:36 +0000 From: Christopher Lameter X-X-Sender: cl@nuc-kabylake To: Matthew Wilcox 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 In-Reply-To: <20190215180852.GJ12668@bombadil.infradead.org> Message-ID: <01000168f26d9e0c-aef3255a-5059-4657-b241-dae66663bbea-000000@email.amazonses.com> 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> <20190215180852.GJ12668@bombadil.infradead.org> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-SES-Outgoing: 2019.02.15-54.240.9.37 Feedback-ID: 1.us-east-1.fQZZZ0Xtj2+TD7V5apTT/NrT6QKuPgzCT/IC7XYgDKI=:AmazonSES 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, 15 Feb 2019, Matthew Wilcox wrote: > > 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. It makes a lot of sense since the filesystems play COW etc games with the pages and RDMA is very much like O_DIRECT in that the pages are modified directly under I/O. It also bypasses the page cache in case you have not noticed yet. Both filesysetms and RDMA acting on a page cache at the same time lead to the mess that we are trying to solve.