Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 609F6C433F5 for ; Fri, 17 Dec 2021 16:41:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239183AbhLQQk7 (ORCPT ); Fri, 17 Dec 2021 11:40:59 -0500 Received: from ams.source.kernel.org ([145.40.68.75]:35892 "EHLO ams.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239189AbhLQQk6 (ORCPT ); Fri, 17 Dec 2021 11:40:58 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id D77E3B82954 for ; Fri, 17 Dec 2021 16:40:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 576C8C36AE8; Fri, 17 Dec 2021 16:40:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1639759255; bh=DuCWxOF8xwW5JZgXvfMFgH5c57m8bIZ61WHsH+oFdhU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=P4LmZfE+x3MA1XLc2RxCqg/y7GwxPw4nBjYm+1Ehsxu8hCKpDJ2iAFY9w2MaAth0b 14mCH2sbG4y7uw66bK1WYXvCj+Qx9ZVJAh34lCqbNRPr47FTCx+Zk43S+pIAST4bMj /gvGCkJgYUXykwwYo9xpkKu//x7AXo0kDHDNWjrgqU8ICRuKcSLlifAmRX8Jd8Uqa6 xPNetUG9TJguYQPxrU+z+o3/xxi502uZXfjRJxtA8qFzBQYVbLg3zkRN7vAGkVPZQP 619/i4CENsIawt2jvx3vsc7oI1/iZyFuIIslUQR19R1qowlMjrKxW34/GmlKTUn63l FW1Chc6eP+UcA== Date: Fri, 17 Dec 2021 08:40:53 -0800 From: Jaegeuk Kim To: Zhiguo Niu Cc: Chao Yu , =?utf-8?B?5aSP6Z2ZIChKaW5nIFhpYSk=?= , linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net Subject: Re: [f2fs-dev] [PATCH Vx 1/1] f2fs: Avoid deadlock between writeback and checkpoint Message-ID: References: <80bc28c5-f050-05a9-e9a8-ff42781a191a@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/17, Zhiguo Niu wrote: > Hi Jaegeuk, > > As f2fs_write_node_pages codes: > > 2060 > blk_start_plug > (&plug > );2061 > > f2fs_sync_node_pages > (sbi > , wbc > , *true*, > FS_NODE_IO );2062 > > blk_finish_plug > (&plug > ); > > > if writeback to sync node pages, blk_statr_plug in line 2060 just do nothing Isn't it a different task's plug, yes? > > > > 3449 > *void* blk_start_plug > (*struct* > blk_plug > *plug )3450 > > {3451 > *struct* task_struct > > *tsk = > current ;3452 > > 3453 > /*3454 > * If this is a nested plug, don't actually assign it.3455 > > */3456 > *if* (tsk ->plug > )3457 > > *return*; > > so the NodeA IO is pulged in writeback and stuck. > > > thanks > > Jaegeuk Kim 于2021年12月17日周五 07:22写道： > > > On 12/14, Jaegeuk Kim wrote: > > > On 12/03, Chao Yu wrote: > > > > On 2021/12/3 2:15, Jaegeuk Kim wrote: > > > > > On 12/02, Chao Yu wrote: > > > > > > On 2021/12/2 6:20, Jaegeuk Kim wrote: > > > > > > > On 11/20, Chao Yu wrote: > > > > > > > > On 2021/11/18 14:46, Chao Yu wrote: > > > > > > > > > On 2021/11/18 0:56, Jaegeuk Kim wrote: > > > > > > > > > > On 11/09, niuzhiguo84@gmail.com wrote: > > > > > > > > > > > From: Zhiguo Niu > > > > > > > > > > > > > > > > > > > > > > There could be a scenario as following: > > > > > > > > > > > The inodeA and inodeB are in b_io queue of writeback > > > > > > > > > > > inodeA : f2fs's node inode > > > > > > > > > > > inodeB : a dir inode with only one dirty pages, and the > > node page > > > > > > > > > > > of inodeB cached into inodeA > > > > > > > > > > > > > > > > > > > > > > writeback: > > > > > > > > > > > > > > > > > > > > > > wb_workfn > > > > > > > > > > > wb_writeback > > > > > > > > > > > blk_start_plug > > > > > > > > > > > loop { > > > > > > > > > > > queue_io > > > > > > > > > > > progress=__writeback_inodes_wb > > > > > > > > > > > __writeback_single_inode > > > > > > > > > > > do_writepages > > > > > > > > > > > f2fs_write_data_pages > > > > > > > > > > > wbc->pages_skipped > > +=get_dirty_pages > > > > > > > > > > > inode->i_state &= ~dirty > > > > > > > > > > > wrote++ > > > > > > > > > > > requeue_inode > > > > > > > > > > > } > > > > > > > > > > > blk_finish_plug > > > > > > > > > > > > > > > > > > > > > > checkpoint: > > > > > > > > > > > > > > > > > > > > > > f2fs_write_checkpoint > > > > > > > > > > > f2fs_sync_dirty_inodes > > > > > > > > > > > filemap_fdatawrite > > > > > > > > > > > do_writepages > > > > > > > > > > > f2fs_write_data_pages > > > > > > > > > > > f2fs_write_single_data_page > > > > > > > > > > > f2fs_do_write_data_page > > > > > > > > > > > set_page_writeback > > > > > > > > > > > f2fs_outplace_write_data > > > > > > > > > > > > > f2fs_update_data_blkaddr > > > > > > > > > > > > > f2fs_wait_on_page_writeback > > > > > > > > > > > inode_dec_dirty_pages > > > > > > > > > > > > > > > > > > > > > > 1. Writeback thread flush inodeA, and push it's bio > > request in task's plug; > > > > > > > > > > > 2. Checkpoint thread writes inodeB's dirty page, and > > then wait its node > > > > > > > > > > > page writeback cached into inodeA which is in > > writeback task's plug > > > > > > > > > > > 3. Writeback thread flush inodeB and skip writing the > > dirty page as > > > > > > > > > > > wb_sync_req[DATA] > 0. > > > > > > > > > > > 4. As none of the inodeB's page is marked as > > PAGECACHE_TAG_DIRTY, writeback > > > > > > > > > > > thread clear inodeB's dirty state. > > > > > > > > > > > 5. Then inodeB is moved from b_io to b_dirty because of > > pages_skipped > 0 > > > > > > > > > > > as checkpoint thread is stuck before dec > > dirty_pages. > > > > > > > > > > > > > > > > > > > > > > This patch collect correct pages_skipped according to > > the tag state in > > > > > > > > > > > page tree of inode > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Zhiguo Niu > > > > > > > > > > > Signed-off-by: Jing Xia > > > > > > > > > > > --- > > > > > > > > > > > fs/f2fs/data.c | 4 +++- > > > > > > > > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > > > > > > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c > > > > > > > > > > > index f4fd6c246c9a..e98628e3868c 100644 > > > > > > > > > > > --- a/fs/f2fs/data.c > > > > > > > > > > > +++ b/fs/f2fs/data.c > > > > > > > > > > > @@ -3237,7 +3237,9 @@ static int > > __f2fs_write_data_pages(struct address_space *mapping, > > > > > > > > > > > return ret; > > > > > > > > > > > skip_write: > > > > > > > > > > > - wbc->pages_skipped += get_dirty_pages(inode); > > > > > > > > > > > + wbc->pages_skipped += > > > > > > > > > > > + mapping_tagged(inode->i_mapping, > > PAGECACHE_TAG_DIRTY) ? > > > > > > > > > > > > > > > > > > > > Is there any race condition to get 0, if there's any dirty > > page? IOWs, it > > > > > > > > > > > > > > > > > > Quoted from Jing Xia's explanation: > > > > > > > > > > > > > > > > > > [T:writeback] [T:checkpoint] > > > > > > > > > > > > > > > > My bad, [1] should be here: > > > > > > > > > > > > > > > > bio contains NodeA was plugged in writeback threads > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > - do_writepages -- sync > > write inodeB, inc wb_sync_req[DATA] > > > > > > > > > - f2fs_write_data_pages > > > > > > > > > - > > f2fs_write_single_data_page -- write last dirty page > > > > > > > > > - > > f2fs_do_write_data_page > > > > > > > > > - set_page_writeback > > -- clear page dirty flag and > > > > > > > > > PAGECACHE_TAG_DIRTY > > tag in radix tree > > > > > > > > > - > > f2fs_outplace_write_data > > > > > > > > > - > > f2fs_update_data_blkaddr > > > > > > > > > - > > f2fs_wait_on_page_writeback -- wait NodeA to writeback here > > > > > > > > > - inode_dec_dirty_pages > > > > > > > > > > > > > > > > > bio contains NodeA was plugged in writeback threads > > > > > > > > > > > > > > > > [1] > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > - writeback_sb_inodes > > > > > > > > > - writeback_single_inode > > > > > > > > > - do_writepages > > > > > > > > > - f2fs_write_data_pages -- skip writepages due to > > wb_sync_req[DATA] > > > > > > > > > - wbc->pages_skipped += get_dirty_pages() -- > > PAGECACHE_TAG_DIRTY is not set but get_dirty_pages() returns one > > > > > > > > > - requeue_inode -- requeue inode to wb->b_dirty queue > > due to non-zero.pages_skipped > > > > > > > > > > > > > > So, my question was why this is the problem? > > > > > > > > > > > > kworker will loop writebacking this requeued inode. > > > > > > > > > > Does it make a problem? > > > > > > > > The problem here is kworker will loop for ever. > > > > > > Could you point out where it goes in the loop? > > > > How can we have NodeA IO being stuck in the plug forever? > > I think f2fs_write_node_pages() should have flushed it before. > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > seems the current condition is just requeuing the inode as > > dirty, but next > > > > > > > > > > flushing time will remove it from dirty list. Is this > > giving too much overheads? > > > > > > > > > > > > > > > > > > I prefer to let writeback thread call blk_flush_plug() after > > skipping > > > > > > > > > writepages() due to wb_sync_req[DATA/NODE] check condition, > > thoughts? > > > > > > > > > > > > > > > > > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c > > > > > > > > > index 9f754aaef558..b6e1ed73f8f5 100644 > > > > > > > > > --- a/fs/f2fs/data.c > > > > > > > > > +++ b/fs/f2fs/data.c > > > > > > > > > @@ -3087,6 +3087,8 @@ static int > > f2fs_write_cache_pages(struct address_space *mapping, > > > > > > > > > /* give a priority to WB_SYNC > > threads */ > > > > > > > > > if > > (atomic_read(&sbi->wb_sync_req[DATA]) && > > > > > > > > > wbc->sync_mode == > > WB_SYNC_NONE) { > > > > > > > > > + if (current->plug) > > > > > > > > > + > > blk_flush_plug(current->plug, false); > > > > > > > > > done = 1; > > > > > > > > > break; > > > > > > > > > } > > > > > > > > > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c > > > > > > > > > index 556fcd8457f3..dd9a817d8dab 100644 > > > > > > > > > --- a/fs/f2fs/node.c > > > > > > > > > +++ b/fs/f2fs/node.c > > > > > > > > > @@ -1946,6 +1946,8 @@ int f2fs_sync_node_pages(struct > > f2fs_sb_info *sbi, > > > > > > > > > if > > (atomic_read(&sbi->wb_sync_req[NODE]) && > > > > > > > > > wbc->sync_mode == > > WB_SYNC_NONE) { > > > > > > > > > done = 1; > > > > > > > > > + if (current->plug) > > > > > > > > > + > > blk_flush_plug(current->plug, false); > > > > > > > > > break; > > > > > > > > > } > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > + get_dirty_pages(inode) : 0; > > > > > > > > > > > trace_f2fs_writepages(mapping->host, wbc, DATA); > > > > > > > > > > > return 0; > > > > > > > > > > > } > > > > > > > > > > > -- > > > > > > > > > > > 2.28.0 > > > > > > > > > > > > > > > > > > > > > > > > > > > _______________________________________________ > > > > > > > > > Linux-f2fs-devel mailing list > > > > > > > > > Linux-f2fs-devel@lists.sourceforge.net > > > > > > > > > > > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel > > > > > > > > > > > > > > > > > > _______________________________________________ > > > Linux-f2fs-devel mailing list > > > Linux-f2fs-devel@lists.sourceforge.net > > > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel > >