From patchwork Sat Jan 9 07:59:00 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 12008029 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=-19.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 48A3AC4361B for ; Sat, 9 Jan 2021 08:01:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2F31C23A5B for ; Sat, 9 Jan 2021 08:01:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726745AbhAIIBM (ORCPT ); Sat, 9 Jan 2021 03:01:12 -0500 Received: from mail.kernel.org ([198.145.29.99]:41210 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726748AbhAIIBG (ORCPT ); Sat, 9 Jan 2021 03:01:06 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 971DF23A7C; Sat, 9 Jan 2021 07:59:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1610179186; bh=D2cLsgvBZJFGW9YnFrwrA+vuwvsBuSsiyb+lhDCp2YA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=r5QndVHWjZk6u7rqhVsoxams/JD8MNoS8E8134pGAOKcfy/W4HnDInVFwg8sbEEFp 7CHWAHWyQGIZoZ94yydkwzpAYhvMJVjbbgEVWlnMuxDKf7+Z2i0RO0Iv7oxCRhCAII AAktC4bPG7raefyxI2t2J3xz9PNXgYIHwLsRDAy+EIJc4gnOYAEg9v30npfco7nljx GorEyuHhWKODU/RpYM79+YYzl5L5vAf1Wdp0QxuBxG+91+l0APfc5JobO+OM+DATCD 12YJuHKBOJhm05uzuD/Za3XLnD6cU5qNsKwkodBMng8GKiyR1lQSs4XDmiU2uqfyk8 G/LTIYYbI+Svw== From: Eric Biggers To: linux-fsdevel@vger.kernel.org Cc: linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, Theodore Ts'o , Christoph Hellwig Subject: [PATCH v2 09/12] fs: improve comments for writeback_single_inode() Date: Fri, 8 Jan 2021 23:59:00 -0800 Message-Id: <20210109075903.208222-10-ebiggers@kernel.org> X-Mailer: git-send-email 2.30.0 In-Reply-To: <20210109075903.208222-1-ebiggers@kernel.org> References: <20210109075903.208222-1-ebiggers@kernel.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org From: Eric Biggers Some comments for writeback_single_inode() and __writeback_single_inode() are outdated or not very helpful, especially with regards to writeback list handling. Update them. Signed-off-by: Eric Biggers Reviewed-by: Christoph Hellwig Reviewed-by: Jan Kara --- fs/fs-writeback.c | 57 +++++++++++++++++++++++++++-------------------- 1 file changed, 33 insertions(+), 24 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index cee1df6e3bd43..e91980f493884 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -1442,9 +1442,15 @@ static void requeue_inode(struct inode *inode, struct bdi_writeback *wb, } /* - * Write out an inode and its dirty pages. Do not update the writeback list - * linkage. That is left to the caller. The caller is also responsible for - * setting I_SYNC flag and calling inode_sync_complete() to clear it. + * Write out an inode and its dirty pages (or some of its dirty pages, depending + * on @wbc->nr_to_write), and clear the relevant dirty flags from i_state. + * + * This doesn't remove the inode from the writeback list it is on, except + * potentially to move it from b_dirty_time to b_dirty due to timestamp + * expiration. The caller is otherwise responsible for writeback list handling. + * + * The caller is also responsible for setting the I_SYNC flag beforehand and + * calling inode_sync_complete() to clear it afterwards. */ static int __writeback_single_inode(struct inode *inode, struct writeback_control *wbc) @@ -1487,9 +1493,10 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc) } /* - * Some filesystems may redirty the inode during the writeback - * due to delalloc, clear dirty metadata flags right before - * write_inode() + * Get and clear the dirty flags from i_state. This needs to be done + * after calling writepages because some filesystems may redirty the + * inode during writepages due to delalloc. It also needs to be done + * after handling timestamp expiration, as that may dirty the inode too. */ spin_lock(&inode->i_lock); dirty = inode->i_state & I_DIRTY; @@ -1524,12 +1531,13 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc) } /* - * Write out an inode's dirty pages. Either the caller has an active reference - * on the inode or the inode has I_WILL_FREE set. + * Write out an inode's dirty data and metadata on-demand, i.e. separately from + * the regular batched writeback done by the flusher threads in + * writeback_sb_inodes(). @wbc controls various aspects of the write, such as + * whether it is a data-integrity sync (%WB_SYNC_ALL) or not (%WB_SYNC_NONE). * - * This function is designed to be called for writing back one inode which - * we go e.g. from filesystem. Flusher thread uses __writeback_single_inode() - * and does more profound writeback list handling in writeback_sb_inodes(). + * To prevent the inode from going away, either the caller must have a reference + * to the inode, or the inode must have I_WILL_FREE or I_FREEING set. */ static int writeback_single_inode(struct inode *inode, struct writeback_control *wbc) @@ -1544,23 +1552,23 @@ static int writeback_single_inode(struct inode *inode, WARN_ON(inode->i_state & I_WILL_FREE); if (inode->i_state & I_SYNC) { - if (wbc->sync_mode != WB_SYNC_ALL) - goto out; /* - * It's a data-integrity sync. We must wait. Since callers hold - * inode reference or inode has I_WILL_FREE set, it cannot go - * away under us. + * Writeback is already running on the inode. For WB_SYNC_NONE, + * that's enough and we can just return. For WB_SYNC_ALL, we + * must wait for the existing writeback to complete, then do + * writeback again if there's anything left. */ + if (wbc->sync_mode != WB_SYNC_ALL) + goto out; __inode_wait_for_writeback(inode); } WARN_ON(inode->i_state & I_SYNC); /* - * Skip inode if it is clean and we have no outstanding writeback in - * WB_SYNC_ALL mode. We don't want to mess with writeback lists in this - * function since flusher thread may be doing for example sync in - * parallel and if we move the inode, it could get skipped. So here we - * make sure inode is on some writeback list and leave it there unless - * we have completely cleaned the inode. + * If the inode is already fully clean, then there's nothing to do. + * + * For data-integrity syncs we also need to check whether any pages are + * still under writeback, e.g. due to prior WB_SYNC_NONE writeback. If + * there are any such pages, we'll need to wait for them. */ if (!(inode->i_state & I_DIRTY_ALL) && (wbc->sync_mode != WB_SYNC_ALL || @@ -1576,8 +1584,9 @@ static int writeback_single_inode(struct inode *inode, wb = inode_to_wb_and_lock_list(inode); spin_lock(&inode->i_lock); /* - * If inode is clean, remove it from writeback lists. Otherwise don't - * touch it. See comment above for explanation. + * If the inode is now fully clean, then it can be safely removed from + * its writeback list (if any). Otherwise the flusher threads are + * responsible for the writeback lists. */ if (!(inode->i_state & I_DIRTY_ALL)) inode_io_list_del_locked(inode, wb);