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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 E3B05C433E0 for ; Sun, 28 Jun 2020 02:35:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BB5CC207E8 for ; Sun, 28 Jun 2020 02:35:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725950AbgF1Cff (ORCPT ); Sat, 27 Jun 2020 22:35:35 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:6842 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725880AbgF1Cfe (ORCPT ); Sat, 27 Jun 2020 22:35:34 -0400 Received: from DGGEMS412-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 9B1649CC2879B92F08CD; Sun, 28 Jun 2020 10:35:32 +0800 (CST) Received: from [10.134.22.195] (10.134.22.195) by smtp.huawei.com (10.3.19.212) with Microsoft SMTP Server (TLS) id 14.3.487.0; Sun, 28 Jun 2020 10:35:27 +0800 Subject: Re: [f2fs-dev] [PATCH] f2fs: avoid readahead race condition To: Jaegeuk Kim , , , References: <20200624012148.180050-1-jaegeuk@kernel.org> From: Chao Yu Message-ID: <368cf853-0411-c237-f0ad-481f78a1eef3@huawei.com> Date: Sun, 28 Jun 2020 10:35:26 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20200624012148.180050-1-jaegeuk@kernel.org> Content-Type: text/plain; charset="windows-1252" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.134.22.195] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/6/24 9:21, Jaegeuk Kim wrote: > If two readahead threads having same offset enter in readpages, every read > IOs are split and issued to the disk which giving lower bandwidth. > > This patch tries to avoid redundant readahead calls. > > Signed-off-by: Jaegeuk Kim > --- > fs/f2fs/data.c | 15 +++++++++++++++ > fs/f2fs/f2fs.h | 1 + > fs/f2fs/super.c | 2 ++ > 3 files changed, 18 insertions(+) > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c > index dfd3225153570..1886d83bc5f15 100644 > --- a/fs/f2fs/data.c > +++ b/fs/f2fs/data.c > @@ -2292,6 +2292,7 @@ static int f2fs_mpage_readpages(struct inode *inode, > unsigned nr_pages = rac ? readahead_count(rac) : 1; > unsigned max_nr_pages = nr_pages; > int ret = 0; > + bool drop_ra = false; > > map.m_pblk = 0; > map.m_lblk = 0; > @@ -2302,6 +2303,17 @@ static int f2fs_mpage_readpages(struct inode *inode, > map.m_seg_type = NO_CHECK_TYPE; > map.m_may_create = false; > > + /* > + * Two readahead threads for same address range can cause race condition > + * which fragments sequential read IOs. So let's avoid each other. > + */ > + if (rac && readahead_count(rac)) { > + if (F2FS_I(inode)->ra_offset == readahead_index(rac)) > + drop_ra = true; I guess you missed to return at somewhere when drop_ra is true? thanks, > + else > + F2FS_I(inode)->ra_offset = readahead_index(rac); > + } > + > for (; nr_pages; nr_pages--) { > if (rac) { > page = readahead_page(rac); > @@ -2368,6 +2380,9 @@ static int f2fs_mpage_readpages(struct inode *inode, > } > if (bio) > __submit_bio(F2FS_I_SB(inode), bio, DATA); > + > + if (rac && readahead_count(rac) && !drop_ra) > + F2FS_I(inode)->ra_offset = -1; > return ret; > } > > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h > index 7fb2a1a334388..753782426feac 100644 > --- a/fs/f2fs/f2fs.h > +++ b/fs/f2fs/f2fs.h > @@ -809,6 +809,7 @@ struct f2fs_inode_info { > struct list_head inmem_pages; /* inmemory pages managed by f2fs */ > struct task_struct *inmem_task; /* store inmemory task */ > struct mutex inmem_lock; /* lock for inmemory pages */ > + pgoff_t ra_offset; /* ongoing readahead offset */ > struct extent_tree *extent_tree; /* cached extent_tree entry */ > > /* avoid racing between foreground op and gc */ > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c > index 7326522057378..80cb7cd358f84 100644 > --- a/fs/f2fs/super.c > +++ b/fs/f2fs/super.c > @@ -1015,6 +1015,8 @@ static struct inode *f2fs_alloc_inode(struct super_block *sb) > /* Will be used by directory only */ > fi->i_dir_level = F2FS_SB(sb)->dir_level; > > + fi->ra_offset = -1; > + > return &fi->vfs_inode; > } > >