From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757667AbXFLSvP (ORCPT ); Tue, 12 Jun 2007 14:51:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757243AbXFLSut (ORCPT ); Tue, 12 Jun 2007 14:50:49 -0400 Received: from brick.kernel.dk ([80.160.20.94]:21793 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757308AbXFLSur (ORCPT ); Tue, 12 Jun 2007 14:50:47 -0400 Date: Tue, 12 Jun 2007 20:48:26 +0200 From: Jens Axboe To: Andrew Morton Cc: Peter Zijlstra , linux-kernel@vger.kernel.org Subject: Re: splice: move balance_dirty_pages_ratelimited() outside of splice actor Message-ID: <20070612184826.GS18832@kernel.dk> References: <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> <20070612114322.dfb4e90c.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070612114322.dfb4e90c.akpm@linux-foundation.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 12 2007, Andrew Morton wrote: > 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 ;) I just love commenting stuff, so I'll treat you to a pipe_buffer commentary as well :-) > What sorts of pages can find themselves inside a pipe_buffer, and which of > these types of pages is the above test detecting? Any type of page, really. But for generic_pipe_buf_steal(), it's a page allocated through alloc_page(). The ops must match the buf contents (hence it's placed in the pipe_buffer, not the pipe itself). So if you shoving different pages in there, then your steal function (and others) must reflect that. -- Jens Axboe