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

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Message-ID: <alpine.LFD.2.00.1203070807220.5117@dhcp-27-109.brq.redhat.com>
Date:	Wed, 7 Mar 2012 08:10:00 +0100 (CET)
From:	Lukas Czerner <lczerner@...hat.com>
To:	"Ted Ts'o" <tytso@....edu>
cc:	Lukas Czerner <lczerner@...hat.com>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 4/4 v2] ext4: Do not discard group with BLOCK_UNINIT
 set

On Tue, 6 Mar 2012, Ted Ts'o wrote:

> 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

Ok, if there is a plan to implement that, I am fine with dropping th
patches. But since this optimization would be helpful for discard, we
can introduce BLOCK_DISCARDED/UNPROVISIONED flag maybe ? Which would be
sen only after discard and cleared with the first allocation ?

Thanks!
-Lukas
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