linux-ext4 - Re: [PATCH 4/4 v2] ext4: Do not discard group with BLOCK

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Message-ID: <20120306221815.GA5472@thunk.org>
Date:	Tue, 6 Mar 2012 17:18:15 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 4/4 v2] ext4: Do not discard group with BLOCK_UNINIT set

On Fri, Mar 02, 2012 at 01:11:58PM +0100, Lukas Czerner wrote:
> Because the BLOCK_UNINIT is only set on mke2fs time and cleared when
> allocation from that group takes place we know that when set, there was
> not anything allocated from that group, hence there should not be anything
> to discard from the file system point of view.

There's a really good reason to set BLOCK_UNINIT once we have noticed
that all of the blocks in the block group have been released....

If you have a 3TB HDD, running e2fsck takes 4 times as long if all of
the block groups have BLOCK_UNINIT cleared, compared to a freshly
mkfs'ed file system.  As a result of my getting really annoyed at how
long it took in this case, I'm planning on making e2fsck clear
BLOCK_UNINIT if possible, so that subsequent e2fsck's (and dumpe2fs
and debugfs invocations) can also be fast.

					- Ted
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