From mboxrd@z Thu Jan 1 00:00:00 1970 From: Theodore Ts'o Subject: Re: [PATCH] jbd2: Optimize jbd2_log_do_checkpoint() a bit Date: Tue, 2 Sep 2014 17:59:30 -0400 Message-ID: <20140902215930.GJ6232@thunk.org> References: <1409678310-11646-1-git-send-email-jack@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-ext4@vger.kernel.org To: Jan Kara Return-path: Received: from imap.thunk.org ([74.207.234.97]:33730 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755315AbaIBWoA (ORCPT ); Tue, 2 Sep 2014 18:44:00 -0400 Content-Disposition: inline In-Reply-To: <1409678310-11646-1-git-send-email-jack@suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Sep 02, 2014 at 07:18:30PM +0200, Jan Kara wrote: > When we discover written out buffer in transaction checkpoint list we > don't have to recheck validity of a transaction. Either this is the last > buffer in a transaction - and then we are done - or this isn't and then > we can just take another buffer from the checkpoint list without > dropping j_list_lock. > > Signed-off-by: Jan Kara > --- > fs/jbd2/checkpoint.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c > index 993a187527f3..3722e2e53638 100644 > --- a/fs/jbd2/checkpoint.c > +++ b/fs/jbd2/checkpoint.c > @@ -343,12 +343,15 @@ restart: > if (!buffer_dirty(bh)) { > if (unlikely(buffer_write_io_error(bh)) && !result) > result = -EIO; > - get_bh(bh); > BUFFER_TRACE(bh, "remove from checkpoint"); > - __jbd2_journal_remove_checkpoint(jh); > - spin_unlock(&journal->j_list_lock); > - __brelse(bh); Currently, all of the places which call __jbd2_jouranl_remove_checkpoint(jh) are doing so with an elevated b_count. For example, see __try_to_free_cp_buf(). After doing a lot of desk checking, I can't see any reason for holding the elevanted b_count, so I think it should be to remove it, but then we can simplify the other uses __try_to_free_cp_buf(). For example, in the loop that I folded from __wait_cp_io, we could drop the done variable and change: done = __jbd2_journal_remove_checkpoint(jh); __brelse(bh); to this: __brelse(bh); if (__jbd2_journal_remove_checkpoint(jh)) break; How much testing have you done of this optimization? I'm tempted to try nuking all of the elevated b_counts around the call to __jbd2_journal_remove_checkpoint(), and then doing a test to see if anything blows up. Cheers, - Ted