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[209.85.208.176]) by smtp.gmail.com with ESMTPSA id b20-20020ac247f4000000b004efff420b0asm649497lfp.108.2023.05.19.09.30.47 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 19 May 2023 09:30:47 -0700 (PDT) Received: by mail-lj1-f176.google.com with SMTP id 38308e7fff4ca-2af222c9e3cso14211031fa.3 for ; Fri, 19 May 2023 09:30:47 -0700 (PDT) X-Received: by 2002:a05:6402:2d5:b0:510:f6e0:7d9f with SMTP id b21-20020a05640202d500b00510f6e07d9fmr2254674edx.13.1684513359285; Fri, 19 May 2023 09:22:39 -0700 (PDT) MIME-Version: 1.0 References: <20230519074047.1739879-1-dhowells@redhat.com> <20230519074047.1739879-10-dhowells@redhat.com> In-Reply-To: From: Linus Torvalds Date: Fri, 19 May 2023 09:22:22 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v20 09/32] tty, proc, kernfs, random: Use direct_splice_read() To: Christoph Hellwig Cc: David Howells , Jens Axboe , Al Viro , Matthew Wilcox , Jan Kara , Jeff Layton , David Hildenbrand , Jason Gunthorpe , Logan Gunthorpe , Hillf Danton , Christian Brauner , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Greg Kroah-Hartman , Christoph Hellwig , John Hubbard , Miklos Szeredi , Arnd Bergmann Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 0980F140013 X-Rspam-User: X-Stat-Signature: 1sh6sujwkqjemxnjzk1cjh8uitsnu5o1 X-Rspamd-Server: rspam01 X-HE-Tag: 1684513849-146356 X-HE-Meta: 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 nQcg1ngb 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 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, May 19, 2023 at 1:12=E2=80=AFAM Christoph Hellwig wrote: > > Pinging Al (and maybe Linus): is there any good reason to not simply > default to direct_splice_read if ->read_iter is implemented and > ->splice_read is not once you remove ITER_PIPE? For me, the reason isn't so much technical as "historical pain". We've had *so* many problems with splice on random file descriptors that I at some point decided "no splice by default". Now, admittedly most of the problems were due to the whole set_fs() ambiguity, which you fixed and no longer exists. So maybe we could go back to "implement splice by default". I agree that as long as the default implementation is obviously safe, it should be ok, and maybe direct_splice_read is that obvious.. Linus