From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757692AbXFLSnw (ORCPT ); Tue, 12 Jun 2007 14:43:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756815AbXFLSno (ORCPT ); Tue, 12 Jun 2007 14:43:44 -0400 Received: from smtp2.linux-foundation.org ([207.189.120.14]:44808 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756277AbXFLSnn (ORCPT ); Tue, 12 Jun 2007 14:43:43 -0400 Date: Tue, 12 Jun 2007 11:43:22 -0700 From: Andrew Morton To: Jens Axboe Cc: Peter Zijlstra , linux-kernel@vger.kernel.org Subject: Re: splice: move balance_dirty_pages_ratelimited() outside of splice actor Message-Id: <20070612114322.dfb4e90c.akpm@linux-foundation.org> In-Reply-To: <20070612181540.GP18832@kernel.dk> References: <20070611163433.dbc541ec.akpm@linux-foundation.org> <20070612063510.GO18832@kernel.dk> <20070612112059.GY18832@kernel.dk> <20070612113101.GZ18832@kernel.dk> <1181649983.7348.309.camel@twins> <20070612121047.GB18832@kernel.dk> <1181650572.7348.312.camel@twins> <20070612124449.GD18832@kernel.dk> <20070612094615.9e5557e5.akpm@linux-foundation.org> <20070612173202.GO18832@kernel.dk> <20070612181540.GP18832@kernel.dk> X-Mailer: Sylpheed version 2.2.7 (GTK+ 2.8.6; i686-pc-linux-gnu) 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 On Tue, 12 Jun 2007 20:15:41 +0200 Jens Axboe wrote: > On Tue, Jun 12 2007, Jens Axboe wrote: > > On Tue, Jun 12 2007, Andrew Morton wrote: > > > On Tue, 12 Jun 2007 14:44:50 +0200 Jens Axboe wrote: > > > > > > > splice > > > > > > btw, I'm staring in profound mystification at this: > > > > > > int generic_pipe_buf_steal(struct pipe_inode_info *pipe, > > > struct pipe_buffer *buf) > > > { > > > struct page *page = buf->page; > > > > > > if (page_count(page) == 1) { > > > lock_page(page); > > > return 0; > > > } > > > > > > return 1; > > > } > > > > > > > > > afacit that `if page_count(page)' test could be replaced by > > > `if today_is_tuesday()'. But then I don't have the foggiest idea > > > what it's trying to do. > > > > > > It would be nice to get some comments in and around here. > > > > > > Also, I was trying to work out the role and responsibility of the ->pin > > > callback, and gave up. > > > > > > There isn't a lot of point in explaining this over email - one should be > > > able to gain an understanding of these things by reading the code. I think > > > the best way of tackling this would be to comprehensively document > > > pipe_buf_operations and pipe_inode_info, please... > > > > OK so I wont explain it in detail here, I'll write up a good set of > > comments tonight. > > I'll merge this into the #splice branch. Great, thanks. > +/** > + * generic_pipe_buf_steal - attempt to take ownership of a @pipe_buffer > + * @pipe: the pipe that the buffer belongs to > + * @buf: the buffer to attempt to steal > + * > + * Description: > + * This function attempts to steal the @struct page attached to > + * @buf. If successful, this function returns 0 and returns with > + * the page locked. The caller may then reuse the page for whatever > + * he wishes, the typical use is insertion into a different file > + * page cache. > + */ > int generic_pipe_buf_steal(struct pipe_inode_info *pipe, > struct pipe_buffer *buf) > { > struct page *page = buf->page; > > + /* > + * A reference of one is golden, that means that the owner of this > + * page is the only one holding a reference to it. lock the page > + * and return OK. > + */ > if (page_count(page) == 1) { > lock_page(page); > return 0; I still don't get this code. I guess I should have asked for pipe_buffer docs too ;) What sorts of pages can find themselves inside a pipe_buffer, and which of these types of pages is the above test detecting?