From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7D28C71143 for ; Fri, 18 Aug 2023 12:42:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376940AbjHRMly convert rfc822-to-8bit (ORCPT ); Fri, 18 Aug 2023 08:41:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38042 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1376953AbjHRMl3 (ORCPT ); Fri, 18 Aug 2023 08:41:29 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EC1973A9F for ; Fri, 18 Aug 2023 05:41:27 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with both STARTTLS and AUTH (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-160-BBNzSMdkOEuOZg1_C6R6rg-1; Fri, 18 Aug 2023 13:41:25 +0100 X-MC-Unique: BBNzSMdkOEuOZg1_C6R6rg-1 Received: from AcuMS.Aculab.com (10.202.163.6) by AcuMS.aculab.com (10.202.163.6) with Microsoft SMTP Server (TLS) id 15.0.1497.48; Fri, 18 Aug 2023 13:41:21 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.048; 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: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Matthew Wilcox > Sent: Friday, August 18, 2023 1:27 PM > > On Fri, Aug 18, 2023 at 12:16:23PM +0000, David Laight wrote: > > > > + ITER_IOVEC = 1, > > > > + ITER_UBUF = 2, > > > > + ITER_KVEC = 4, > > > > + ITER_BVEC = 8, > > > > + ITER_XARRAY = 16, > > > > + ITER_DISCARD = 32, > > > > IIRC Linus had type:6 - that doesn't leave any headroom > > for additional types (even though they shouldn't proliferate). > > 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. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)