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Date: Mon, 07 Sep 2009 19:48:02 -0400
From: Ric Wheeler <ricwheeler@...il.com>
To: Eric Sandeen <sandeen@...hat.com>
CC: Theodore Ts'o <tytso@....edu>,
Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 2/2] ext4: Automatically enable journal_async_commit on
ext4 file systems
Eric Sandeen wrote:
> Theodore Ts'o wrote:
>> Now that we have cleaned up journal_async_commit, it's safe to enable
>> it all the time. But we only want to do so if ext4-specific INCOMPAT
>> features are enabled, since otherwise we will prevent the filesystem
>> from being mounted using ext3.
>
> Has anyone done some serious power-fail/crash (real or simulated)
> testing with this? If not, I think we should before it's default...
>
> -Eric
I think that we also need to see some very compelling performance
numbers to justify the complexity. Journaling is complex enough, so if
this is not a win, we should (in my opinion) go with the simplest
technique :-)
ric
>
>> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
>> ---
>> Documentation/filesystems/ext4.txt | 8 ++++++--
>> fs/ext4/super.c | 26 ++++++++++++++++++++++++--
>> 2 files changed, 30 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/filesystems/ext4.txt
>> b/Documentation/filesystems/ext4.txt
>> index 3e329db..4f8d73a 100644
>> --- a/Documentation/filesystems/ext4.txt
>> +++ b/Documentation/filesystems/ext4.txt
>> @@ -135,8 +135,12 @@ ro Mount filesystem read
>> only. Note that ext4 will
>> writes to the filesystem.
>>
>> journal_async_commit Commit block can be written to disk without
>> waiting
>> - for descriptor blocks. If enabled older kernels cannot
>> - mount the device.
>> + for descriptor blocks. This mount option will be
>> + automatically enabled if ext4-specific INCOMPAT
>> + features are present in the file system.
>> +
>> +nojournal_async_commit Disable the journal_async_commit option, even
>> + for ext4 filesystems.
>>
>> journal=update Update the ext4 file system's journal to the
>> current
>> format.
>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>> index f1815d3..f644a5c 100644
>> --- a/fs/ext4/super.c
>> +++ b/fs/ext4/super.c
>> @@ -75,6 +75,15 @@ static int ext4_unfreeze(struct super_block *sb);
>> static void ext4_write_super(struct super_block *sb);
>> static int ext4_freeze(struct super_block *sb);
>>
>> +/*
>> + * If ext4 filesystem features are enabled, then enable async_commits
>> + * by default.
>> + */
>> +#define ASYNC_COMMIT_DEFAULT(sb) (EXT4_HAS_INCOMPAT_FEATURE(sb, \
>> + (EXT4_FEATURE_INCOMPAT_EXTENTS| \
>> + EXT4_FEATURE_INCOMPAT_64BIT| \
>> + EXT4_FEATURE_INCOMPAT_FLEX_BG)))
>> +
>>
>> ext4_fsblk_t ext4_block_bitmap(struct super_block *sb,
>> struct ext4_group_desc *bg)
>> @@ -845,8 +854,13 @@ static int ext4_show_options(struct seq_file
>> *seq, struct vfsmount *vfs)
>> */
>> seq_puts(seq, ",barrier=");
>> seq_puts(seq, test_opt(sb, BARRIER) ? "1" : "0");
>> - if (test_opt(sb, JOURNAL_ASYNC_COMMIT))
>> - seq_puts(seq, ",journal_async_commit");
>> + if (ASYNC_COMMIT_DEFAULT(sb)) {
>> + if (!test_opt(sb, JOURNAL_ASYNC_COMMIT))
>> + seq_puts(seq, ",nojournal_async_commit");
>> + } else {
>> + if (test_opt(sb, JOURNAL_ASYNC_COMMIT))
>> + seq_puts(seq, ",journal_async_commit");
>> + }
>> if (test_opt(sb, NOBH))
>> seq_puts(seq, ",nobh");
>> if (test_opt(sb, I_VERSION))
>> @@ -1050,6 +1064,7 @@ enum {
>> Opt_commit, Opt_min_batch_time, Opt_max_batch_time,
>> Opt_journal_update, Opt_journal_dev,
>> Opt_journal_checksum, Opt_journal_async_commit,
>> + Opt_nojournal_async_commit,
>> Opt_abort, Opt_data_journal, Opt_data_ordered, Opt_data_writeback,
>> Opt_data_err_abort, Opt_data_err_ignore, Opt_mb_history_length,
>> Opt_usrjquota, Opt_grpjquota, Opt_offusrjquota, Opt_offgrpjquota,
>> @@ -1092,6 +1107,7 @@ static const match_table_t tokens = {
>> {Opt_journal_dev, "journal_dev=%u"},
>> {Opt_journal_checksum, "journal_checksum"},
>> {Opt_journal_async_commit, "journal_async_commit"},
>> + {Opt_nojournal_async_commit, "nojournal_async_commit"},
>> {Opt_abort, "abort"},
>> {Opt_data_journal, "data=journal"},
>> {Opt_data_ordered, "data=ordered"},
>> @@ -1284,6 +1300,9 @@ static int parse_options(char *options, struct
>> super_block *sb,
>> case Opt_journal_async_commit:
>> set_opt(sbi->s_mount_opt, JOURNAL_ASYNC_COMMIT);
>> break;
>> + case Opt_nojournal_async_commit:
>> + clear_opt(sbi->s_mount_opt, JOURNAL_ASYNC_COMMIT);
>> + break;
>> case Opt_noload:
>> set_opt(sbi->s_mount_opt, NOLOAD);
>> break;
>> @@ -2422,6 +2441,9 @@ static int ext4_fill_super(struct super_block
>> *sb, void *data, int silent)
>> */
>> set_opt(sbi->s_mount_opt, DELALLOC);
>>
>> + if (ASYNC_COMMIT_DEFAULT(sb))
>> + set_opt(sbi->s_mount_opt, JOURNAL_ASYNC_COMMIT);
>> +
>> if (!parse_options((char *) data, sb, &journal_devnum,
>> &journal_ioprio, NULL, 0))
>> goto failed_mount;
>
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