From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 28 Oct 2002 21:30:54 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 28 Oct 2002 21:30:54 -0500 Received: from pizda.ninka.net ([216.101.162.242]:24239 "EHLO pizda.ninka.net") by vger.kernel.org with ESMTP id ; Mon, 28 Oct 2002 21:30:52 -0500 Date: Mon, 28 Oct 2002 18:27:57 -0800 (PST) Message-Id: <20021028.182757.77947646.davem@redhat.com> To: axboe@suse.de Cc: linux-kernel@vger.kernel.org, akpm@digeo.com Subject: Re: [patch][cft] zero-copy dma cd writing and ripping From: "David S. Miller" In-Reply-To: <20021028161857.GK2937@suse.de> References: <20021028155401.GI2937@suse.de> <1035822310.8970.9.camel@rth.ninka.net> <20021028161857.GK2937@suse.de> X-FalunGong: Information control. X-Mailer: Mew version 2.1 on Emacs 21.1 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org From: Jens Axboe Date: Mon, 28 Oct 2002 17:18:57 +0100 A related question. get_user_pages() does page_cache_get() on the page, except if it's reserved. First question is 'why' doesn't it do that on a reserved page? We get this conditional when mapping, and the unmapping needs to check for reserved as well before doing page_cache_release(). Surely the extra reference would be ok to hold for PageReserved pages as well? The basic behavior of the whole MM for reserved pages is supposed to be to not do any kind of reference counting, COW'ing, etc. on them. Any deviation from this behavior is going to lead to problems and can be considered a bug until some later time at which we decide to change this behavior. Look at how copy_page_range() deals with reserved pages, for example. This logic is all over the VM.