linux-ext4 - Re: Incompatibility between mballoc and online resize

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Message-id: <20080610062445.GH3726@webber.adilger.int>
Date:	Tue, 10 Jun 2008 00:24:45 -0600
From:	Andreas Dilger <adilger@....com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	Alex Tomas <alex.tomas@....com>, linux-ext4@...r.kernel.org
Subject: Re: Incompatibility between mballoc and online resize

On Jun 09, 2008  23:46 -0400, Theodore Ts'o wrote:
> I've been trying to track down the problems in ext4's online-resizing,
> and one of the ones which is most noticeable is that online resizing
> mballoc has some specific data structures which need to be enlarged when
> the number of block groups in the filesystem are grown dynamically.
> 
> Specifically, the s_group_info array; in the current ext4 patch queue,
> this isn't happening, which means after the online resizing operation,
> when the filesystem is unmounted, ext4_put_super() calls
> ext4_mb_release(), which then iterates over s_group_info array, and then
> this triggers a kernel oops.
> 
> Is clusterfs running with mballoc in production?  If so, how was this
> problem fixed?  Did we miss a patch to make sure that on-line resizing
> worked with mballoc enabled?

When Lustre is mounting the backing filesystem on the server, there is
no ext3 mountpoint visible to userspace, hence no access to the underlying
filesystem to pass the resize ioctl to, so we haven't had this problem
yet.  We filed a bug on it, for the time that we can pass an ioctl through:

https://bugzilla.lustre.org/show_bug.cgi?id=15208

We have another open bug related to resize2fs and uninit_bg, but that
is for offline resizing:

https://bugzilla.lustre.org/show_bug.cgi?id=12002

Both of these bugs are mere placeholders, they don't have any patches.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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