From patchwork Sat Feb 9 21:53:46 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Theodore Ts'o X-Patchwork-Id: 219454 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id AD0382C008D for ; Sun, 10 Feb 2013 08:54:01 +1100 (EST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760855Ab3BIVx7 (ORCPT ); Sat, 9 Feb 2013 16:53:59 -0500 Received: from li9-11.members.linode.com ([67.18.176.11]:47607 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760837Ab3BIVxz (ORCPT ); Sat, 9 Feb 2013 16:53:55 -0500 Received: from root (helo=closure.thunk.org) by imap.thunk.org with local-esmtp (Exim 4.80) (envelope-from ) id 1U4IMt-0001Zv-4T; Sat, 09 Feb 2013 21:53:55 +0000 Received: by closure.thunk.org (Postfix, from userid 15806) id 53B812E93EE; Sat, 9 Feb 2013 16:53:52 -0500 (EST) From: Theodore Ts'o To: Ext4 Developers List Cc: Theodore Ts'o Subject: [PATCH 06/12] ext4: grab page before starting transaction handle in write_begin() Date: Sat, 9 Feb 2013 16:53:46 -0500 Message-Id: <1360446832-12724-7-git-send-email-tytso@mit.edu> X-Mailer: git-send-email 1.7.12.rc0.22.gcdd159b In-Reply-To: <1360446832-12724-1-git-send-email-tytso@mit.edu> References: <1360446832-12724-1-git-send-email-tytso@mit.edu> X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on imap.thunk.org); SAEximRunCond expanded to false Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org The grab_cache_page_write_begin() function can potentially sleep for a long time, since it may need to do memory allocation which can block if the system is under significant memory pressure, and because it may be blocked on page writeback. If it does take a long time to grab the page, it's better that we not hold an active jbd2 handle. So grab a handle on the page first, and _then_ start the transaction handle. This commit fixes the following long transaction handle hold time: postmark-2917 [000] .... 196.435786: jbd2_handle_stats: dev 254,32 tid 570 type 2 line_no 2541 interval 311 sync 0 requested_blocks 1 dirtied_blocks 0 Signed-off-by: "Theodore Ts'o" --- fs/ext4/inode.c | 111 ++++++++++++++++++++++++++++++++++---------------------- 1 file changed, 68 insertions(+), 43 deletions(-) diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index c3c47e2..38164a8 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -906,32 +906,40 @@ static int ext4_write_begin(struct file *file, struct address_space *mapping, ret = ext4_try_to_write_inline_data(mapping, inode, pos, len, flags, pagep); if (ret < 0) - goto out; - if (ret == 1) { - ret = 0; - goto out; - } + return ret; + if (ret == 1) + return 0; } -retry: + /* + * grab_cache_page_write_begin() can take a long time if the + * system is thrashing due to memory pressure, or if the page + * is being written back. So grab it first before we start + * the transaction handle. This also allows us to allocate + * the page (if needed) without using GFP_NOFS. + */ +retry_grab: + page = grab_cache_page_write_begin(mapping, index, flags); + if (!page) + return -ENOMEM; + unlock_page(page); + +retry_journal: handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE, needed_blocks); if (IS_ERR(handle)) { - ret = PTR_ERR(handle); - goto out; + page_cache_release(page); + return PTR_ERR(handle); } - /* We cannot recurse into the filesystem as the transaction is already - * started */ - flags |= AOP_FLAG_NOFS; - - page = grab_cache_page_write_begin(mapping, index, flags); - if (!page) { + lock_page(page); + if (page->mapping != mapping) { + /* The page got truncated from under us */ + unlock_page(page); + page_cache_release(page); ext4_journal_stop(handle); - ret = -ENOMEM; - goto out; + goto retry_grab; } - - *pagep = page; + wait_on_page_writeback(page); if (ext4_should_dioread_nolock(inode)) ret = __block_write_begin(page, pos, len, ext4_get_block_write); @@ -946,7 +954,6 @@ retry: if (ret) { unlock_page(page); - page_cache_release(page); /* * __block_write_begin may have instantiated a few blocks * outside i_size. Trim these off again. Don't need @@ -970,11 +977,14 @@ retry: if (inode->i_nlink) ext4_orphan_del(NULL, inode); } - } - if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries)) - goto retry; -out: + if (ret == -ENOSPC && + ext4_should_retry_alloc(inode->i_sb, &retries)) + goto retry_journal; + page_cache_release(page); + return ret; + } + *pagep = page; return ret; } @@ -2524,42 +2534,52 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping, pos, len, flags, pagep, fsdata); if (ret < 0) - goto out; - if (ret == 1) { - ret = 0; - goto out; - } + return ret; + if (ret == 1) + return 0; } -retry: + /* + * grab_cache_page_write_begin() can take a long time if the + * system is thrashing due to memory pressure, or if the page + * is being written back. So grab it first before we start + * the transaction handle. This also allows us to allocate + * the page (if needed) without using GFP_NOFS. + */ +retry_grab: + page = grab_cache_page_write_begin(mapping, index, flags); + if (!page) + return -ENOMEM; + unlock_page(page); + /* * With delayed allocation, we don't log the i_disksize update * if there is delayed block allocation. But we still need * to journalling the i_disksize update if writes to the end * of file which has an already mapped buffer. */ +retry_journal: handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE, 1); if (IS_ERR(handle)) { - ret = PTR_ERR(handle); - goto out; + page_cache_release(page); + return PTR_ERR(handle); } - /* We cannot recurse into the filesystem as the transaction is already - * started */ - flags |= AOP_FLAG_NOFS; - page = grab_cache_page_write_begin(mapping, index, flags); - if (!page) { + lock_page(page); + if (page->mapping != mapping) { + /* The page got truncated from under us */ + unlock_page(page); + page_cache_release(page); ext4_journal_stop(handle); - ret = -ENOMEM; - goto out; + goto retry_grab; } - *pagep = page; + /* In case writeback began while the page was unlocked */ + wait_on_page_writeback(page); ret = __block_write_begin(page, pos, len, ext4_da_get_block_prep); if (ret < 0) { unlock_page(page); ext4_journal_stop(handle); - page_cache_release(page); /* * block_write_begin may have instantiated a few blocks * outside i_size. Trim these off again. Don't need @@ -2567,11 +2587,16 @@ retry: */ if (pos + len > inode->i_size) ext4_truncate_failed_write(inode); + + if (ret == -ENOSPC && + ext4_should_retry_alloc(inode->i_sb, &retries)) + goto retry_journal; + + page_cache_release(page); + return ret; } - if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries)) - goto retry; -out: + *pagep = page; return ret; }