linux-ext4 - Re: [PATCH 3/3] mke2fs: prevent creation of unmountable ext4 with large flex

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Date:	Fri, 13 Jun 2014 15:45:03 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	Akira Fujita <a-fujita@...jp.nec.com>,
	Theodore Tso <tytso@....edu>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 3/3] mke2fs: prevent creation of unmountable ext4 with large flex_bg count

On Jun 12, 2014, at 5:50 PM, Darrick J. Wong <darrick.wong@...cle.com> wrote:
> On Wed, Jun 11, 2014 at 01:01:29PM -0600, Andreas Dilger wrote:
>> 
>> This also reminds me of my previous flex_bg patch:
>> [PATCH][RFC] mke2fs: handle flex_bg collision with backup descriptors
>> http://permalink.gmane.org/gmane.comp.file-systems.ext4/42298
>> 
>> which fixes the "bmap-imap-itable-bmap-imap-itable" problem when a large
>> flex_bg size is used.  Sadly, there were no comments on that patch.
> 
> I had wondered if you were planning to address the FIXMEs in the patch, but
> then forgot to ever follow up... :/

Well, I was thinking that the patch was good enough to land as-is.  It fixes 99% the problem for flex_bg size up to 65536, but only 95% of the groups for flex_bg of 131072.  I guess I'll send it out again without [RFC], and if people start using flex_bg >= 131072 (which is enough for all the metadata in a 16TB chunk) then we can work out the final details.  I suspect that the sparse_super2 feature would probably become more prevalent and avoid this problem entirely.

Cheers, Andreas

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