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Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <8F8B62FD-0F16-4383-BB34-97E850DAA7AF@hammerspace.com> References: <8F8B62FD-0F16-4383-BB34-97E850DAA7AF@hammerspace.com> <3DFBF27C-A62B-4AFE-87FD-3DF53FC39E8E@hammerspace.com> <20230316152618.711970-1-dhowells@redhat.com> <20230316152618.711970-28-dhowells@redhat.com> <754534.1678983891@warthog.procyon.org.uk> To: Trond Myklebust Cc: dhowells@redhat.com, Matthew Wilcox , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Alexander Viro , Christoph Hellwig , Jens Axboe , Jeffrey Layton , Christian Brauner , Linus Torvalds , "netdev@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Anna Schumaker , Charles Edward Lever , "linux-nfs@vger.kernel.org" Subject: Re: [RFC PATCH 27/28] sunrpc: Use sendmsg(MSG_SPLICE_PAGES) rather then sendpage MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <809994.1678990010.1@warthog.procyon.org.uk> Date: Thu, 16 Mar 2023 18:06:50 +0000 Message-ID: <809995.1678990010@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 9C3EC80025 X-Stat-Signature: scj1hnk1kecxh6zetjuz138exrqk8y9d X-Rspam-User: X-HE-Tag: 1678990018-922378 X-HE-Meta: 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 B/aBw0pw C3yl5KN380C8iVkwimQnPhLm2QouJdpEPNoyM9GPrivUg4VRoIAtLxEFoTX4kHn5WsstiZxNvRzpM99rJ1xqyOk+l3faRj5f6wXuqGQuFn7IG1Cmh98Oww04MNHG90pyL4ZguVGOmGpe1ZQ62+Fw6Sp2vCzkZgE8u3lxpqOs7PrQQHnFRyMLjJjAkuFnY6R4Ud+5zSWjTzX7tjr286J+2eRbdt7AeDykWe/7xX7ndDL26pS5jKIIy/rot0FTD+fX4c0kytBoSlPcFzbrrLClcSWG0/wUuMqsxMavrl93z8YEyvVDQe9uQFuLbU9m3jaZ8GwVV 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: Trond Myklebust wrote: > 1) This is code that is common to the client and the server. Why are we > adding unused 3 bvec slots to every client RPC call? Fair point, but I'm trying to avoid making four+ sendmsg calls in nfsd rather than one. > 2) It obfuscates the existence of these bvec slots. True, it'd be nice to find a better way to do it. Question is, can the client make use of MSG_SPLICE_PAGES also? > 3) knfsd may use splice_direct_to_actor() in order to avoid copying the page > cache data into private buffers (it just takes a reference to the > pages). Using MSG_SPLICE_PAGES will presumably require it to protect those > pages against further writes while the socket is referencing them. Upstream sunrpc is using sendpage with TCP. It already has that issue. MSG_SPLICE_PAGES is a way of doing sendpage through sendmsg. David