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 105AAC433FE for ; Tue, 14 Dec 2021 19:02:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237293AbhLNTCB (ORCPT ); Tue, 14 Dec 2021 14:02:01 -0500 Received: from ams.source.kernel.org ([145.40.68.75]:54008 "EHLO ams.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234429AbhLNTB7 (ORCPT ); Tue, 14 Dec 2021 14:01:59 -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 3800BB81667 for ; Tue, 14 Dec 2021 19:01:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D4347C34600; Tue, 14 Dec 2021 19:01:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1639508517; bh=3jXrjZMUUllEdVwoHar50e5mfi/E6/goCnlo3Lz/d3Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Z5RWaNZf3h+K3cZO7BKPXE2aPLe7DyBOZphnGPwhh4RITP98hSzfDlXIROpFB3aE0 6eiVK/Jazsjt5FV0QYZmRRuCubq9+dJtUrrkRho1t5dCBzFyYWOqjhhRpO9uU4gFxl TiVzv8sP3C881eg1uwyGITX395VS+lALMMQ5LoahRkBAX3nQzWcaHGywG/tFmceS3F oE8B2GA7iIg6KztwL7oRjfrGmnuH8pCjcxvXlZyxFB3tXvwVDwP7dwVDvYKkSBKxwV h5AvCLTTrBvC6/R6DweiBLgIba0L4yyXZPRQyyHLAG+HfD/4mLCMm2zMA7F/nxTRYs Rk0WU65btqDHQ== Date: Tue, 14 Dec 2021 11:01:55 -0800 From: Jaegeuk Kim To: Chao Yu Cc: niuzhiguo84@gmail.com, Jing.Xia@unisoc.com, 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: <1636438608-27597-1-git-send-email-niuzhiguo84@gmail.com> <80bc28c5-f050-05a9-e9a8-ff42781a191a@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <80bc28c5-f050-05a9-e9a8-ff42781a191a@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? > > 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 > > > > > >