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=-13.9 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 D9FACC433E9 for ; Thu, 3 Sep 2020 16:10:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B5FA520716 for ; Thu, 3 Sep 2020 16:10:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728654AbgICQKQ (ORCPT ); Thu, 3 Sep 2020 12:10:16 -0400 Received: from pegase1.c-s.fr ([93.17.236.30]:37149 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727065AbgICQKP (ORCPT ); Thu, 3 Sep 2020 12:10:15 -0400 Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4Bj5PG5Yv8zB09ZM; Thu, 3 Sep 2020 18:10:10 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id O-5sjIVtz4zX; Thu, 3 Sep 2020 18:10:10 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4Bj5PG4nykzB09ZK; Thu, 3 Sep 2020 18:10:10 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 02F3D8B807; Thu, 3 Sep 2020 18:10:10 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id 1FKxObY2whfQ; Thu, 3 Sep 2020 18:10:10 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 7AECE8B801; Thu, 3 Sep 2020 18:10:07 +0200 (CEST) Subject: Re: [PATCH] /dev/zero: also implement ->read To: Christoph Hellwig , arnd@arndb.de, gregkh@linuxfoundation.org Cc: linux-kernel@vger.kernel.org References: <20200903155922.1111551-1-hch@lst.de> From: Christophe Leroy Message-ID: <55d1ecb8-4a0c-fa58-d3cf-bf6796eea7bd@csgroup.eu> Date: Thu, 3 Sep 2020 18:05:41 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200903155922.1111551-1-hch@lst.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 03/09/2020 à 17:59, Christoph Hellwig a écrit : > Christophe reported a major speedup due to avoiding the iov_iter > overhead, so just add this trivial function. Note that /dev/zero > already implements both an iter and non-iter writes so this just > makes it more symmetric. > > Christophe Leroy > Signed-off-by: Christoph Hellwig Tested-by: Christophe Leroy > --- > drivers/char/mem.c | 22 ++++++++++++++++++++++ > 1 file changed, 22 insertions(+) > > diff --git a/drivers/char/mem.c b/drivers/char/mem.c > index abd4ffdc8cdebc..1dc99ab158457a 100644 > --- a/drivers/char/mem.c > +++ b/drivers/char/mem.c > @@ -726,6 +726,27 @@ static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter) > return written; > } > > +static ssize_t read_zero(struct file *file, char __user *buf, > + size_t count, loff_t *ppos) > +{ > + size_t cleared = 0; > + > + while (count) { > + size_t chunk = min_t(size_t, count, PAGE_SIZE); > + > + if (clear_user(buf + cleared, chunk)) > + return cleared ? cleared : -EFAULT; > + cleared += chunk; > + count -= chunk; > + > + if (signal_pending(current)) > + return cleared ? cleared : -ERESTARTSYS; > + cond_resched(); > + } > + > + return cleared; > +} > + > static int mmap_zero(struct file *file, struct vm_area_struct *vma) > { > #ifndef CONFIG_MMU > @@ -921,6 +942,7 @@ static const struct file_operations zero_fops = { > .llseek = zero_lseek, > .write = write_zero, > .read_iter = read_iter_zero, > + .read = read_zero, > .write_iter = write_iter_zero, > .mmap = mmap_zero, > .get_unmapped_area = get_unmapped_area_zero, >