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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3A13FC678DC for ; Fri, 18 Aug 2023 12:16:35 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9EAA794005D; Fri, 18 Aug 2023 08:16:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 99A89940053; Fri, 18 Aug 2023 08:16:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 861F094005D; Fri, 18 Aug 2023 08:16:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 75DE1940053 for ; Fri, 18 Aug 2023 08:16:34 -0400 (EDT) Received: from smtpin13.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 433C1A11A4 for ; Fri, 18 Aug 2023 12:16:34 +0000 (UTC) X-FDA: 81137123508.13.F043A8D Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by imf14.hostedemail.com (Postfix) with ESMTP id 5B877100012 for ; Fri, 18 Aug 2023 12:16:30 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=aculab.com; spf=pass (imf14.hostedemail.com: domain of david.laight@aculab.com designates 185.58.85.151 as permitted sender) smtp.mailfrom=david.laight@aculab.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1692360992; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=KMNQfuGtsOXOQkuENIJ7cvlVqqjkqbDztekhcLsm2qw=; b=nlqiJ4WmQof61sbM5ZHxT3Zo1BvKLCc/iJC61svoRg1zGjm7pizO/gOD05I35VmfJQuv2+ BzQCpfFBiixH0DvMtv4YV+x+k9az3Vb5mYSkXuR+Yiydpw2Hf+EU9IJNU75NxGxkc3GAun WJNFBUXu/yVmTTYgIUQAfmN/hxrVb6A= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=aculab.com; spf=pass (imf14.hostedemail.com: domain of david.laight@aculab.com designates 185.58.85.151 as permitted sender) smtp.mailfrom=david.laight@aculab.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1692360992; a=rsa-sha256; cv=none; b=URrfuHRwQ8UFtbIhlIpQM2hBtytclmH0v0LfAO1JlnHFiM0TqMuttbV9awv4rv1z+ySxK6 PQQ4buaP/WznYyviWEw7dDQmaMFbAhiS1h3mfTMClLnXXD6YZ6suqN2xa5T7eO6F3l6Qyp h+c8AfS0+LR8ykR/dcAu7NNEPe9HNX8= 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-202-98C0T_vJOJK6bOwFbwR9Yw-1; Fri, 18 Aug 2023 13:16:27 +0100 X-MC-Unique: 98C0T_vJOJK6bOwFbwR9Yw-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 13:16:23 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.048; Fri, 18 Aug 2023 13:16:23 +0100 From: David Laight To: 'David Howells' , Linus Torvalds CC: Al Viro , Jens Axboe , "Christoph Hellwig" , Christian Brauner , "Matthew Wilcox" , 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+zJggAAE0WA= Date: Fri, 18 Aug 2023 12:16:23 +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: <1748360.1692358952@warthog.procyon.org.uk> 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-Rspam-User: X-Stat-Signature: akw38dce37kzbmnt9srb6n9abi8q9t9s X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 5B877100012 X-HE-Tag: 1692360990-630094 X-HE-Meta: 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 h+mCPbQD OY79epGtzre2Iziy1jzSD8yMHFTuyLJ93yjrzUj8SHsldkoDoWzM6Oxh99uC7aFlMgDMpu5X1hIuRZMu0mQJRxIkR1afRTCxzO4h4ZZm01UZHY7GiCv6cZk2Qm87/Bfo5TOJillJ4mkpJNLoNOZZ+d2pCoz5thg1MUIoY8ifPQXLVj84uwAvPcy+mM6Muy/FTWneNY84ussqUaR5SHJOInKnD13gn2/vnQ8dqVxgcWLeG2L5UkrvS56WdVrILz/xu+ylAxRGF4H4SmS3qHKk3QyOtqM9GOw+5Lxk5aJ4rarzn2DF3p1ypTY2E3NTr9rVZZ+ySpu4V04ULccUSWv0i1ECfCQ== 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: David Howells > Sent: Friday, August 18, 2023 12:43 PM >=20 > Linus Torvalds wrote: >=20 > > Well, that part is trivially fixable, and we should do that anyway for > > other reasons. > > .. > > enum iter_type { > > =09/* iter types */ > > -=09ITER_IOVEC, > > -=09ITER_KVEC, > > -=09ITER_BVEC, > > -=09ITER_XARRAY, > > -=09ITER_DISCARD, > > -=09ITER_UBUF, > > +=09ITER_IOVEC =3D 1, > > +=09ITER_UBUF =3D 2, > > +=09ITER_KVEC =3D 4, > > +=09ITER_BVEC =3D 8, > > +=09ITER_XARRAY =3D 16, > > +=09ITER_DISCARD =3D 32, That could be zero - no bits and default. > > }; >=20 > It used to be this way, but Al switched it: >=20 > =098cd54c1c848031a87820e58d772166ffdf8c08c0 > =09iov_iter: separate direction from flavour Except it also had the direction flag inside the enum. That caused its own piles of grief. IIRC Linus had type:6 - that doesn't leave any headroom for additional types (even though they shouldn't proliferate). It may be best to avoid bits 15+ (in a bitfield) due to issues with large constants and sign extension. On x86 (I think) 'and immediate' and 'bit test' are the same size for bit 0 to 7, BIT wins for higher bits. gcc generates strange code for some initialisers (see yesterday's thread) and you definitely mustn't leave unused bits in a bitfield. Might be better is the fields are assigned later! (I also saw clang carefully preserving %eax on stabck!) =09David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales)