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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT 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 CC107C43387 for ; Tue, 18 Dec 2018 12:33:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 97E2520874 for ; Tue, 18 Dec 2018 12:33:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="FZt34N9g" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726674AbeLRMdu (ORCPT ); Tue, 18 Dec 2018 07:33:50 -0500 Received: from pandora.armlinux.org.uk ([78.32.30.218]:41376 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726451AbeLRMdu (ORCPT ); Tue, 18 Dec 2018 07:33:50 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2014; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=g2wZq5y5ENq8UiNCs5gTLmGTpkFs7b8zTmrQA3nLddI=; b=FZt34N9gz4KJHOfktbCTFkJtG ymyudHAlx7rpGiuKIqR4CE+fMN4mR+7EO6TbDipXIxtphrOZj3gOpNQvk1UXpkC+ShOovF1tI4pct vLdyQWzmQg0/qHisevw/R6lyHdLM+iCLHG+ks3IJGsFwYz7eXkHS0ajNnmU2HY3yLibuw=; Received: from n2100.armlinux.org.uk ([2002:4e20:1eda:1:214:fdff:fe10:4f86]:44710) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.90_1) (envelope-from ) id 1gZEYt-00066i-5v; Tue, 18 Dec 2018 12:33:23 +0000 Received: from linux by n2100.armlinux.org.uk with local (Exim 4.90_1) (envelope-from ) id 1gZEYq-0007Kf-Ll; Tue, 18 Dec 2018 12:33:20 +0000 Date: Tue, 18 Dec 2018 12:33:19 +0000 From: Russell King - ARM Linux To: Souptick Joarder Cc: Michal Hocko , Heiko Stuebner , linux-rockchip@lists.infradead.org, airlied@linux.ie, hjc@rock-chips.com, Matthew Wilcox , linux-kernel@vger.kernel.org, Linux-MM , dri-devel@lists.freedesktop.org, Andrew Morton , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v4 4/9] drm/rockchip/rockchip_drm_gem.c: Convert to use vm_insert_range Message-ID: <20181218123318.GN26090@n2100.armlinux.org.uk> References: <20181217202334.GA11758@jordon-HP-15-Notebook-PC> <20181218095709.GJ26090@n2100.armlinux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 18, 2018 at 05:36:04PM +0530, Souptick Joarder wrote: > On Tue, Dec 18, 2018 at 3:27 PM Russell King - ARM Linux > wrote: > > This looks like a change in behaviour. > > > > If user_count is zero, and offset is zero, then we pass into > > vm_insert_range() a page_count of zero, and vm_insert_range() does > > nothing and returns zero. > > > > However, as we can see from the above code, the original behaviour > > was to return -ENXIO in that case. > > I think these checks are not necessary. I am not sure if we get into mmap > handlers of driver with user_count = 0. I'm not sure either, I'm just pointing out the change of behaviour. > > The other thing that I'm wondering is that if (eg) count is 8 (the > > object is 8 pages), offset is 2, and the user requests mapping 6 > > pages (user_count = 6), then we call vm_insert_range() with a > > pages of rk_obj->pages + 2, and a pages_count of 6 - 2 = 4. So we > > end up inserting four pages. > > Considering the scenario, user_count will remain 8 (user_count = > vma_pages(vma) ). ? No ? > Then we call vm_insert_range() with a pages of rk_obj->pages + 2, and > a pages_count > of 8 - 2 = 6. So we end up inserting 6 pages. > > Please correct me if I am wrong. vma_pages(vma) is the number of pages that the user requested, it is the difference between vma->vm_end and vma->vm_start in pages. As I said above, "the user requests mapping 6 pages", so vma_pages() will be 6, and so user_count will also be 6. You are passing user_count - offset into vm_insert_range(), which will be 6 - 2 = 4 in my example. This is two pages short of what the user requested. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up