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Wed, 16 Aug 2023 13:28:47 +0100 From: David Laight To: 'David Howells' , Al Viro , Linus Torvalds CC: 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 Date: Wed, 16 Aug 2023 12:28:47 +0000 Message-ID: <03730b50cebb4a349ad8667373bb8127@AcuMS.aculab.com> References: <20230816120741.534415-1-dhowells@redhat.com> <20230816120741.534415-3-dhowells@redhat.com> In-Reply-To: <20230816120741.534415-3-dhowells@redhat.com> 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-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: B7C811C002C X-Stat-Signature: geti9i5q85f79z1ijf5inswy5jgfe6dg X-Rspam-User: X-HE-Tag: 1692188935-47024 X-HE-Meta: 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 fagoxnmV mjP31vDZpLJSk5PSoQ+7jwM+8KcHLBTLjQuYnofcwjDuIC4dzP9Wjv6as3atM9ZVuowZFYj4oeFH1ada9QpbHS1GN7ecr4hszOn7XEpyaI3zouTkTOSWtfEoHmuVFbIYNExMCyo9rTgc8dTfR7JwEHMXbKQ60lS5tz49jGj4168An0JTrRYi4LR2JLeIUJ7ubAjvFUIhuTrabpDxGpVr/5FnMUbKR6/y/GbNVvSVYY0QKTvQFM58K+oYosAIfbqigrA72BCwNg/+GlMgzNGCearArZg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: David Howells > Sent: Wednesday, August 16, 2023 1:08 PM Given: > iter->copy_mc is only used with a bvec iterator and only by > dump_emit_page() in fs/coredump.c so rather than handle this in > memcpy_from_iter_mc() where it is checked repeatedly by _copy_from_iter()= and > copy_page_from_iter_atomic(), Instead of adding the extra check to every copy: > +static __always_inline > +size_t __copy_from_iter(void *addr, size_t bytes, struct iov_iter *i) > +{ > +=09if (unlikely(iov_iter_is_copy_mc(i))) > +=09=09return __copy_from_iter_mc(addr, bytes, i); > +=09return iterate_and_advance(i, bytes, addr, > +=09=09=09=09 copy_from_user_iter, memcpy_from_iter); > } Couldn't the relevant code directly call __copy_frtom_iter_mc() ? Or a version then checked iov_is_copy_mc() and then fell back to the standard function. =09David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales)