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Fri, 18 Aug 2023 13:41:21 +0100 From: David Laight To: 'Matthew Wilcox' CC: 'David Howells' , Linus Torvalds , Al Viro , "Jens Axboe" , Christoph Hellwig , Christian Brauner , Jeff Layton , "linux-fsdevel@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH v3 2/2] iov_iter: Don't deal with iter->copy_mc in memcpy_from_iter_mc() Thread-Topic: [PATCH v3 2/2] iov_iter: Don't deal with iter->copy_mc in memcpy_from_iter_mc() Thread-Index: AQHZ0DpP/l59sWTPXU+UuQ9VGbJikq/s16Kg///6foCAACRpIIAC+zJggAAE0WD///bMgIAAEYXg Date: Fri, 18 Aug 2023 12:41:21 +0000 Message-ID: References: <03730b50cebb4a349ad8667373bb8127@AcuMS.aculab.com> <20230816120741.534415-1-dhowells@redhat.com> <20230816120741.534415-3-dhowells@redhat.com> <608853.1692190847@warthog.procyon.org.uk> <3dabec5643b24534a1c1c51894798047@AcuMS.aculab.com> <665724.1692218114@warthog.procyon.org.uk> <1748360.1692358952@warthog.procyon.org.uk> In-Reply-To: Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Stat-Signature: knmzt8d4hr7nbtezihjn6yyiuz6t3wfr X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 92F21100014 X-Rspam-User: X-HE-Tag: 1692362489-146824 X-HE-Meta: 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 vb7PtuD0 WOpBlra6SUhCx+dX864UBIHM5wyegbaM9BO9thGxU7Y3n2AAj6vp4cNi/xbbT6o3qWSAeKc3yAK15wSkIflT8jpwgine+EKMjQovJAgNxIupmFRcnJ7GBaywrak3OpF9k9DobdV2S9EBg+nabHTGkqjjRfOinijplCbIQXJ+7mj1A+LxIUBJgKYMZvb5dHHI36kkVlht3vZJrZWIqr/EaTQVY1tGtMK2B8ZRk9HTqKCOAs0BJH29YKf9TFjbbQ8pLzMS2GeF9fPU2QlRRpisHXJNgeQ== 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: From: Matthew Wilcox > Sent: Friday, August 18, 2023 1:27 PM >=20 > On Fri, Aug 18, 2023 at 12:16:23PM +0000, David Laight wrote: > > > > +=09ITER_IOVEC =3D 1, > > > > +=09ITER_UBUF =3D 2, > > > > +=09ITER_KVEC =3D 4, > > > > +=09ITER_BVEC =3D 8, > > > > +=09ITER_XARRAY =3D 16, > > > > +=09ITER_DISCARD =3D 32, > > > > IIRC Linus had type:6 - that doesn't leave any headroom > > for additional types (even though they shouldn't proliferate). >=20 > I have proposed an ITER_KBUF in the past (it is to KVEC as UBUF is > to IOVEC). I didn't care enough to keep pushing it, but it's clearly > a common idiom. Indeed, I didn't spot UBUF going in - I spot a lot of stuff. I did wonder if you could optimise for a vector length of 1 (inside the KVEC conditional). That would also pick up the cases where there only happens to be a single buffer. I also remember writing a patch that simplified import_iovec() by combining the iov_iter with a struct iovec iovec[UIO_FASTIOV]. All got bogged down in io_uring which would need changing first. =09David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales)