Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933630Ab0KQKKO (ORCPT ); Wed, 17 Nov 2010 05:10:14 -0500 Received: from cn.fujitsu.com ([222.73.24.84]:60281 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S932951Ab0KQKKM (ORCPT ); Wed, 17 Nov 2010 05:10:12 -0500 Message-ID: <4CE3AA37.8060709@cn.fujitsu.com> Date: Wed, 17 Nov 2010 18:11:03 +0800 From: Miao Xie Reply-To: miaox@cn.fujitsu.com User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100413 Fedora/3.0.4-2.fc13 Thunderbird/3.0.4 MIME-Version: 1.0 To: Josef Bacik CC: viro@zeniv.linux.org.uk, Chris Mason , Linux Fsdevel , Linux Kernel , Linux Btrfs , Andrew Morton , Ito Subject: Re: [PATCH 1/3] direct-io: add a hook for the fs to provide its own bio merging check function References: <4CE3579B.1000301@cn.fujitsu.com> <20101117070658.GF5618@dhcp231-156.rdu.redhat.com> <20101117093720.GG5618@dhcp231-156.rdu.redhat.com> In-Reply-To: <20101117093720.GG5618@dhcp231-156.rdu.redhat.com> X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.1FP4|July 25, 2010) at 2010-11-17 18:10:32, Serialize by Router on mailserver/fnst(Release 8.5.1FP4|July 25, 2010) at 2010-11-17 18:10:32, Serialize complete at 2010-11-17 18:10:32 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=ISO-8859-1; format=flowed Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2176 Lines: 52 Hi, Josef On wed, 17 Nov 2010 04:37:21 -0500, Josef Bacik wrote: >> Heh so I was going to fix this after the hole punching stuff. The fact is btrfs >> maps everything that is ok to do in one IO via get_blocks(). So all we need to >> do is add another DIO_ flag to tell us to treat each get_blocks() call as >> discrete. I wanted to use buffer_boundary for this, but I think it's too >> drastic of a change for people who already use buffer_boundary(); >> >> What happens today is that say we map 4k, we do submit_page_section, but if this >> is our first bit of IO we just set dio->cur_page and such and then loop again. >> Say there is 4k-hole-4k, we do the next mapping and set buffer_boundary again, >> and come into submit_page_section and because cur_page is set, we do >> dio_send_cur_page. Because there is no dio->bio we setup a new bio, but when we >> do that we clear dio->boundary, and leave the bio all setup. So the next time >> we loop around the tail 4k gets added to our previously setup bio and boom we >> hit this problem with btrfs. >> >> If we can add a DIO_GET_BLOCKS_DISCRETE or some other such non-sense then we can >> easily kill all the logical offset code I had and just make some simple changes >> to make the DIO stuff work for us. All we do is in get_more_blocks we do >> >> if ((dio->flags& DIO_GET_BLOCKS_DISCRETE)&& dio->bio) >> dio_submit_bio(dio); >> > > Right after I went to bed I realized this should be > > if (dio->flags& DIO_GET_BLOCKS_DISCRETE) { > if (dio->cur_page) { > dio_send_cur_page(dio); > page_cache_release(dio->cur_page); > dio->cur_page = NULL; > } > > if (dio->bio) > dio_submit_bio(dio); > } As far as I know, get_block() can not make sure the IO doesn't span the chunks or stripes. Maybe we can do this check in get_blocks(). In this way, we needn't change vfs. I have written the patch and is testing it now. Up to now, it works well. Thanks Miao -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/