linux-ext4 - Re: [PATCH] mke2fs: Add support for lazy journal initialization

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Message-Id: <7925BD53-B86D-4ED6-8EA1-20A00DB7D4C0@dilger.ca>
Date:	Mon, 7 Feb 2011 08:29:09 -0800
From:	Andreas Dilger <adilger.kernel@...ger.ca>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	Ted Ts'o <tytso@....EDU>, ext4 List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] mke2fs: Add support for lazy journal initialization

On 2011-02-07, at 06:15, Lukas Czerner wrote:
> On Thu, 3 Feb 2011, Andreas Dilger wrote:
>> This patch adds the ability to skip zeroing the journal on disk.  This can
>> significantly speed up mke2fs with large journals.  At worst the uninitialized
>> journal is only a very short-term risk (if at all), because the journal will
>> be overwritten on any new filesystem as soon as any significant amount of data
>> is written to disk, unlike lazy_itable_init which can leave uninitialized
>> itable blocks indefinitely (in the absence of the kernel init thread).
> 
> I think that we can skip the journal zeroing if the underlying device,
> or the journal device supports discard, and advertise that discard
> zeroes data. It is the same behavior as in the case of inode tables and
> it would be nice to have the same thing for journal. Are you planning to
> implement this as well ?

That detection didn't exist when I originally wrote that patch.  It definitely makes sense to default to not zeroing the journal if discard has been done.

Cheers, Andreas





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