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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 11054C43466 for ; Mon, 21 Sep 2020 15:29:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C25632085B for ; Mon, 21 Sep 2020 15:29:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727630AbgIUP3p (ORCPT ); Mon, 21 Sep 2020 11:29:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50794 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727629AbgIUP3p (ORCPT ); Mon, 21 Sep 2020 11:29:45 -0400 Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E1774C061755; Mon, 21 Sep 2020 08:29:44 -0700 (PDT) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kKNl3-003CV3-6n; Mon, 21 Sep 2020 15:29:37 +0000 Date: Mon, 21 Sep 2020 16:29:37 +0100 From: Al Viro To: David Laight Cc: Christoph Hellwig , Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-mips@vger.kernel.org" , "linux-parisc@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-s390@vger.kernel.org" , "sparclinux@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-aio@kvack.org" , "io-uring@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-mm@kvack.org" , "netdev@vger.kernel.org" , "keyrings@vger.kernel.org" , "linux-security-module@vger.kernel.org" Subject: Re: [PATCH 02/11] mm: call import_iovec() instead of rw_copy_check_uvector() in process_vm_rw() Message-ID: <20200921152937.GX3421308@ZenIV.linux.org.uk> References: <20200921143434.707844-1-hch@lst.de> <20200921143434.707844-3-hch@lst.de> <20200921150211.GS3421308@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Mon, Sep 21, 2020 at 03:21:35PM +0000, David Laight wrote: > You really don't want to be looping through the array twice. Profiles, please. > I think the 'length' check can be optimised to do something like: > for (...) { > ssize_t len = (ssize_t)iov[seg].iov_len; > ret += len; > len_hi += (unsigned long)len >> 20; > } > if (len_hi) { > /* Something potentially odd in the lengths. > * Might just be a very long fragment. > * Check the individial values. */ > Add the exiting loop here. > } Far too ugly to live.