linux-ext4 - Re: [PATCH v2] ext4: Deprecate data=journal mount option

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Date:	Fri, 12 Aug 2011 09:25:24 +0100
From:	Ric Wheeler <rwheeler@...hat.com>
To:	Lukas Czerner <lczerner@...hat.com>
CC:	Andreas Dilger <adilger@...ger.ca>,
	linux-ext4 List <linux-ext4@...r.kernel.org>,
	"Theodore Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
	Eric Sandeen <sandeen@...hat.com>
Subject: Re: [PATCH v2] ext4: Deprecate data=journal mount option

On 08/12/2011 09:16 AM, Lukas Czerner wrote:
> On Thu, 11 Aug 2011, Andreas Dilger wrote:
>
>> On 2011-08-11, at 9:01 AM, Lukas Czerner wrote:
>>> On Tue, 28 Jun 2011, Lukas Czerner wrote:
>>>> Data journalling mode (data=journal) is known to be neglected by
>>>> developers and only minority of people is actually using it. This
>>>> mode is also less tested than the other two modes by the developers.
>>>>
>>>> This creates a dangerous combination, because the option which seems
>>>> *safer* is actually less safe the others. So this commit adds a warning
>>>> message in case that data=journal mode is used, so the user is informed
>>>> that the mode might be removed in the future.
>>> Any comments on this ? Is that feasible to remove is someday ?
>> I'm less in favour of removing data=journal.  Jan made some fixes to
>> data=journal mode in the last few weeks, which means that people are
>> still using this.
> I think that Jan was actually the one who was in favour of this change
> IIRC. But you're right that there are still some (very little possibly?)
> users of this. But this change does not remove it, but just let the
> users know that it might be removed someday, hence discouraging them from
> using it.
>
> Also we were discussing that several times, so I think that letting
> users know that we are considering it is a good thing.
>
> Thanks!
> -Lukas

I think that this will be very useful to have - users should definitely chime in 
when they see this warning if they are using data journal mode.

The only work load that I know that benefits from a performance point of view is 
one which involves an fsync() heavy, small file creation workload.  Any workload 
with larger files tends to lose roughly 50% of the write bandwidth under 
streaming writes since we end up writing everything twice.

Regards,

Ric


>
>>>> Signed-off-by: Lukas Czerner<lczerner@...hat.com>
>>>> ---
>>>> fs/ext4/super.c |    5 +++++
>>>> 1 files changed, 5 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>>>> index 9ea71aa..9d189cf 100644
>>>> --- a/fs/ext4/super.c
>>>> +++ b/fs/ext4/super.c
>>>> @@ -1631,6 +1631,11 @@ static int parse_options(char *options, struct super_block *sb,
>>>> 			sbi->s_min_batch_time = option;
>>>> 			break;
>>>> 		case Opt_data_journal:
>>>> +			ext4_msg(sb, KERN_WARNING,
>>>> +				 "Using data=journal may be removed in the "
>>>> +				 "future. Please, contact "
>>>> +				 "linux-ext4@...r.kernel.org if you are "
>>>> +				 "using this feature.");
>>>> 			data_opt = EXT4_MOUNT_JOURNAL_DATA;
>>>> 			goto datacheck;
>>>> 		case Opt_data_ordered:
>>>>
>>> --
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>>
>> Cheers, Andreas
>>
>>
>>
>>
>>
>>

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