linux-ext4 - Re: Need of revoke mechanism in JBD

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Date:	Tue, 26 Apr 2011 17:23:21 +0800
From:	Ding Dinghua <dingdinghua85@...il.com>
To:	Yongqiang Yang <xiaoqiangnk@...il.com>
Cc:	Niraj Kulkarni <kulkarniniraj14@...il.com>,
	linux-ext4@...r.kernel.org
Subject: Re: Need of revoke mechanism in JBD

I think it's not only a performance issue but more important, a
correctness issue.
Revoke table is used for preventing the wrong replay of journal which
cause data corruption:
If block A has been journalled its modification, committed to journal
and hasn't been checkpointed,
and in later transactions block A is freed and reused for data in
no-journalled-data mode, then If
we don't have revoke table which recording the releasing event, replay
of journal will overwrite the new data,
which causing data corruption.

2011/4/26 Yongqiang Yang <xiaoqiangnk@...il.com>:
> AFAIK, it can accelerate the recovering process.  If a block is in the
> revoke table of a transaction t1 and t1 is committed, then the there
> is no need to recover the block in transactions which is earlier than
> t1.
>
> On Tue, Apr 26, 2011 at 4:29 PM, Niraj Kulkarni
> <kulkarniniraj14@...il.com> wrote:
>> Hi all,
>>      I am new to fs development. I am trying to modify the journal structure
>> of JBD. While analyzing the code, I could understand most of the things, but
>> I am not able to understand the need of revoke mechanism. Can anybody
>> enlighten me on this issue?
>>
>> Regards
>> Niraj
>> --
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>
>
>
> --
> Best Wishes
> Yongqiang Yang
> --
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-- 
Ding Dinghua
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