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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <03730b50cebb4a349ad8667373bb8127@AcuMS.aculab.com> References: <03730b50cebb4a349ad8667373bb8127@AcuMS.aculab.com> <20230816120741.534415-1-dhowells@redhat.com> <20230816120741.534415-3-dhowells@redhat.com> To: David Laight Cc: dhowells@redhat.com, Al Viro , Linus Torvalds , 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() MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <608852.1692190847.1@warthog.procyon.org.uk> Date: Wed, 16 Aug 2023 14:00:47 +0100 Message-ID: <608853.1692190847@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 X-Rspam-User: X-Stat-Signature: srhrczjzka81a85zz4tx5a3wzs7bhybh X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 1232BC000B X-HE-Tag: 1692190855-390846 X-HE-Meta: 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 0YQTQ940 FVZel+hOPNJ+E9mKGKa7QUCMH+esYsPEoNai9Kkw+XLOXqQofwhjIp4DRf4dwjL788WJAhhzx5g03GfdwYbRv1Q7+Zpg2R58dBtknDnnkXuR8IiMmIlPoZd/BKzS672KVcpP7jFFjAVI8JeRlQIogZ2/Ytnz6BifpnfqY7mNNTaTXDSjqjJFBf/eYxsfX4Yj2dHRvRZAIy7iSDQdoCQ7LHKO9900OYLh1n64HhnWIOvWqD0WwUYeaHS/f0dGkTecTn2gGbaSQNJzHdDeR62ImHO4T2/AhMiCKPr/73cJAnRnP72U= 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: David Laight wrote: > > Couldn't the relevant code directly call __copy_from_iter_mc() ? > Or a version then checked iov_is_copy_mc() and then fell > back to the standard function. No, because the marked iterator is handed by the coredump code to __kernel_write_iter() and thence on to who-knows-what driver - which will call copy_from_iter() or some such. $DRIVER shouldn't need to know about ->copy_mc. One thing I do wonder about, though, is what should happen if they call, say, csum_and_copy_from_iter()? That doesn't have an _mc variant. Or what if they extract the pages and operate directly on those? David