linux-ext4 - Re: [PATCH] resize2fs: support online-resizing for meta

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Message-ID: <20120903230030.GF5066@thunk.org>
Date:	Mon, 3 Sep 2012 19:00:30 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Kai Grosshaus <kai@...l.de>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] resize2fs: support online-resizing for meta_bg and
 64bits features

On Mon, Sep 03, 2012 at 11:02:17PM +0200, Kai Grosshaus wrote:
> 
> is offline resizeing possible with this patch without online resize
> kernel patches (i use 3.2.0) with this features?
> 
> Filesystem features:      has_journal ext_attr dir_index filetype
> needs_recovery meta_bg extent 64bit flex_bg sparse_super large_file
> huge_file uninit_bg dir_nlink extra_isize
> 
> I had no luck offline resizing my 24TB fs with e2fstools version
> 1.42 and 1.42.5.

No, offline resizing for 64-bit file systems (and file systems with
meta_bg) hasn't been implemented yet.  It's on the todo list, but the
main issue is that for many of the ext4 developers, our employers
don't require the use of large RAID arrays, so the development has
been somewhat delayed between my work responsibilities and organizing
the kernel summit last week in San Diego.  Yongqiang's patches were
posted for review quite some time ago, but I knew they needed some
review and reworking, and it just didn't rise to the top of the
priority heap until now.

(I'm technically on vacation this week in Santa Fe, and hacking online
resizing for ext4 is fun, so I've been using the early morning and
late nights to finally get around to making forward progress for
online resize.  :-)

Technically, off-line shrink for meta_bg/64-bit file systems is easy,
and off-line growth isn't fundamentally hard, but it simply requires
teaching resize2fs about the new meta_bg and flex_bg formats.  It's
probably only a week or so, full-time, by someone who really
understands the code in question.  The only problem is the only person
who understands that code deeply is me, and I've just been completely
swamped these last couple of months.  Hopefully, now that the kernel
summit is behind me, I'll have a bit more time to work on off-line
resize, as well as reviewing the many other patches for ext4 which
have been submitted in the past few months (i.e., the extent status
tree, which enables SEEK_HOLE and fixing the bigalloc ENOSPC problem
with delalloc bufferred writes, and the inline data patches).

I suspect that for people who really want to be able to grow their
large 64-bit ext4 file systems, the best path forward will be for me
to backport the on-line resizing (for enlarging 64-bit file systems)
patches to 3.2.x, once I'm convinced we've shaken out all of the bugs
and they are well-tested.

Technically, they wouldn't be material for the 3.2.x stable branch
since they're not a bugfix, but if some distro using 3.2 is willing to
sponsor them, we could make the case that since one or more distro's
are willing to use them in shipping product, they should be in 3.2.x.
(Or I could just abuse the fact that no one is currently actively
enforcing rules around the criteria for stable tree patches, but that
would just be bad kernel developer citizenship.  :-)

Regards,

					- Ted
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