From: akpm@linux-foundation.org Subject: + jbd-fix-the-way-the-b_modified-flag-is-cleared.patch added to -mm tree Date: Fri, 29 Feb 2008 16:04:03 -0800 Message-ID: <200803010004.m210434b027541@imap1.linux-foundation.org> Cc: jbacik@redhat.com, jack@ucw.cz, linux-ext4@vger.kernel.org To: mm-commits@vger.kernel.org Return-path: Received: from smtp1.linux-foundation.org ([207.189.120.13]:59354 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754374AbYCAAFQ (ORCPT ); Fri, 29 Feb 2008 19:05:16 -0500 Sender: linux-ext4-owner@vger.kernel.org List-ID: The patch titled jbd: fix the way the b_modified flag is cleared has been added to the -mm tree. Its filename is jbd-fix-the-way-the-b_modified-flag-is-cleared.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find out what to do about this The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: jbd: fix the way the b_modified flag is cleared From: Josef Bacik Currently at the start of a journal commit we loop through all of the buffers on the committing transaction and clear the b_modified flag (the flag that is set when a transaction modifies the buffer) under the j_list_lock. The problem is that everywhere else this flag is modified only under the jbd lock buffer flag, so it will race with a running transaction who could potentially set it, and have it unset by the committing transaction. This is also a big waste, you can have several thousands of buffers that you are clearing the modified flag on when you may not need to. This patch removes this code and instead clears the b_modified flag upon entering do_get_write_access/journal_get_create_access, so if that transaction does indeed use the buffer then it will be accounted for properly, and if it does not then we know we didn't use it. That will be important for the next patch in this series. Tested thoroughly by myself using postmark/iozone/bonnie++. Signed-off-by: Josef Bacik Cc: Cc: Jan Kara Signed-off-by: Andrew Morton --- fs/jbd/commit.c | 16 ---------------- fs/jbd/transaction.c | 13 +++++++++++++ 2 files changed, 13 insertions(+), 16 deletions(-) diff -puN fs/jbd/commit.c~jbd-fix-the-way-the-b_modified-flag-is-cleared fs/jbd/commit.c --- a/fs/jbd/commit.c~jbd-fix-the-way-the-b_modified-flag-is-cleared +++ a/fs/jbd/commit.c @@ -407,22 +407,6 @@ void journal_commit_transaction(journal_ jbd_debug (3, "JBD: commit phase 2\n"); /* - * First, drop modified flag: all accesses to the buffers - * will be tracked for a new trasaction only -bzzz - */ - spin_lock(&journal->j_list_lock); - if (commit_transaction->t_buffers) { - new_jh = jh = commit_transaction->t_buffers->b_tnext; - do { - J_ASSERT_JH(new_jh, new_jh->b_modified == 1 || - new_jh->b_modified == 0); - new_jh->b_modified = 0; - new_jh = new_jh->b_tnext; - } while (new_jh != jh); - } - spin_unlock(&journal->j_list_lock); - - /* * Now start flushing things to disk, in the order they appear * on the transaction lists. Data blocks go first. */ diff -puN fs/jbd/transaction.c~jbd-fix-the-way-the-b_modified-flag-is-cleared fs/jbd/transaction.c --- a/fs/jbd/transaction.c~jbd-fix-the-way-the-b_modified-flag-is-cleared +++ a/fs/jbd/transaction.c @@ -609,6 +609,12 @@ repeat: goto done; /* + * this is the first time this transaction is touching this buffer, + * reset the modified flag + */ + jh->b_modified = 0; + + /* * If there is already a copy-out version of this buffer, then we don't * need to make another one */ @@ -820,9 +826,16 @@ int journal_get_create_access(handle_t * if (jh->b_transaction == NULL) { jh->b_transaction = transaction; + + /* first access by this transaction */ + jh->b_modified = 0; + JBUFFER_TRACE(jh, "file as BJ_Reserved"); __journal_file_buffer(jh, transaction, BJ_Reserved); } else if (jh->b_transaction == journal->j_committing_transaction) { + /* first access by this transaction */ + jh->b_modified = 0; + JBUFFER_TRACE(jh, "set next transaction"); jh->b_next_transaction = transaction; } _ Patches currently in -mm which might be from jbacik@redhat.com are jbd-fix-the-way-the-b_modified-flag-is-cleared.patch jbd2-fix-the-way-the-b_modified-flag-is-cleared.patch jbd-fix-possible-journal-overflow-issues.patch jbd2-fix-possible-journal-overflow-issues.patch