From: Jan Kara Subject: Re: barriers off by default? Date: Fri, 16 May 2008 02:21:45 +0200 Message-ID: <20080516002145.GA24369@duck.suse.cz> References: <482868A5.1000102@redhat.com> <20080515144355.GB19325@atrey.karlin.mff.cuni.cz> <482CA094.20703@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: ext4 development To: Eric Sandeen Return-path: Received: from styx.suse.cz ([82.119.242.94]:47373 "EHLO mail.suse.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751569AbYEPAVr (ORCPT ); Thu, 15 May 2008 20:21:47 -0400 Content-Disposition: inline In-Reply-To: <482CA094.20703@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu 15-05-08 15:44:04, Eric Sandeen wrote: > Jan Kara wrote: > > >> As I look at my shiny new 500G disks with 32MB of cache, I find myself > >> wondering why the default for ext3 and ext4 is to have barriers disabled. > >> > >> This is a pretty dangerous default w.r.t. filesystem integrity on power > >> loss, no? > >> > > JFYI: SUSE kernel carries for ages a patch which changes this default. > > I'd be more than happy to drop it ;). > > > > Honza > > > What do folks think of this? > > the show_options change is a little funky since jbd may do a test > write and fail... (actually I was thinking maybe at fill_super we > should do a test barrier write and get it out of the way early...) Yes, the patch looks fine with me. Acked-by: Jan Kara > diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt > index b45f3c1..daab1f5 100644 > --- a/Documentation/filesystems/ext3.txt > +++ b/Documentation/filesystems/ext3.txt > @@ -52,8 +52,16 @@ commit=nrsec (*) Ext3 can be told to sync all its data and metadata > Setting it to very large values will improve > performance. > > -barrier=1 This enables/disables barriers. barrier=0 disables > - it, barrier=1 enables it. > +barrier=<0|1(*)> This enables/disables the use of write barriers in > + the jbd code. barrier=0 disables, barrier=1 enables. > + This also requires an IO stack which can support > + barriers, and if jbd gets an error on a barrier > + write, it will disable again with a warning. > + Write barriers enforce proper on-disk ordering > + of journal commits, making volatile disk write caches > + safe to use, at some performance penalty. If > + your disks are battery-backed in one way or another, > + disabling barriers may safely improve performance. > > orlov (*) This enables the new Orlov block allocator. It is > enabled by default. > diff --git a/fs/ext3/super.c b/fs/ext3/super.c > index fe3119a..d06e0f3 100644 > --- a/fs/ext3/super.c > +++ b/fs/ext3/super.c > @@ -555,6 +555,7 @@ static int ext3_show_options(struct seq_file *seq, struct vfsmount *vfs) > struct super_block *sb = vfs->mnt_sb; > struct ext3_sb_info *sbi = EXT3_SB(sb); > struct ext3_super_block *es = sbi->s_es; > + journal_t *journal = EXT3_SB(sb)->s_journal; > unsigned long def_mount_opts; > > def_mount_opts = le32_to_cpu(es->s_default_mount_opts); > @@ -613,8 +614,16 @@ static int ext3_show_options(struct seq_file *seq, struct vfsmount *vfs) > seq_printf(seq, ",commit=%u", > (unsigned) (sbi->s_commit_interval / HZ)); > } > - if (test_opt(sb, BARRIER)) > - seq_puts(seq, ",barrier=1"); > + if (!test_opt(sb, BARRIER)) { > + seq_puts(seq, ",barrier=0"); > + } else { > + /* > + * jbd inherits the barrier flag from ext3, and jbd may actually > + * turn off barriers if a write fails, so it's the real test. > + */ > + if (journal && !(journal->j_flags & JFS_BARRIER)) > + seq_puts(seq, ",barrier=1(failed)"); > + } > if (test_opt(sb, NOBH)) > seq_puts(seq, ",nobh"); > > @@ -1589,6 +1598,7 @@ static int ext3_fill_super (struct super_block *sb, void *data, int silent) > sbi->s_resgid = le16_to_cpu(es->s_def_resgid); > > set_opt(sbi->s_mount_opt, RESERVATION); > + set_opt(sbi->s_mount_opt, BARRIER); > > if (!parse_options ((char *) data, sb, &journal_inum, &journal_devnum, > NULL, 0)) > -- Jan Kara SUSE Labs, CR