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Date: Fri, 27 Jul 2001 01:49:00 +1000
From: Andrew Morton <akpm@zip.com.au>
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To: Daniel Phillips <phillips@bonn-fries.net>
CC: Matthias Andree <matthias.andree@stud.uni-dortmund.de>,
        Alan Cox <alan@lxorguk.ukuu.org.uk>,
        Rik van Riel <riel@conectiva.com.br>,
        lkml <linux-kernel@vger.kernel.org>,
        "ext3-users@redhat.com" <ext3-users@redhat.com>
Subject: Re: ext3-2.4-0.9.4
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Daniel Phillips wrote:
> 
> Ext3 does *not* leave a
> lot of dirty blocks hanging around in normal operation, so sync is not
> nearly as slow as it is with good old Ext2.

eek.

In fully-journalled data mode, we write everything to the journal
in a linear chunk, wait on it, write a commit block, wait on that
and then release all the just-journalled data into the main
filesystem for conventional bdflush/kupdate writeback in twenty
seconds time.

Calling anything which uses fsync_dev() would cause all that writeback
data to be written out and waited on, with the consequential seeking
storm.  Disastrous.

Note that fsync() is OK - in full data journalling mode nothing
is ever attached to i_dirty_buffers.

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