From: Eric Sandeen Subject: Re: barriers off by default? Date: Thu, 15 May 2008 15:44:04 -0500 Message-ID: <482CA094.20703@redhat.com> References: <482868A5.1000102@redhat.com> <20080515144355.GB19325@atrey.karlin.mff.cuni.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: ext4 development To: Jan Kara Return-path: Received: from mx1.redhat.com ([66.187.233.31]:38228 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751546AbYEOUoN (ORCPT ); Thu, 15 May 2008 16:44:13 -0400 In-Reply-To: <20080515144355.GB19325@atrey.karlin.mff.cuni.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: 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...) -Eric 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))