Message-ID: <20150430170527.GH11592@birch.djwong.org>
Date:	Thu, 30 Apr 2015 10:05:27 -0700
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	Chanho Park <chanho61.park@...sung.com>, linux-ext4@...r.kernel.org
Subject: Re: [e2fsprogs] resizing to minimum was failed since 45a78b

On Thu, Apr 30, 2015 at 11:13:16AM -0400, Theodore Ts'o wrote:
> On Thu, Apr 30, 2015 at 07:12:04PM +0900, Chanho Park wrote:
> > 
> > In my situation, I usually use the "resize2fs -M" when making a tizen
> > platform image. As you know, like android, tizen also uses ext4 filesystem
> > and flash the image from bootloader. Instead of flashing full image size, we
> > only flash shrinked filesystem image to reduce flashing time and want to
> > avoid download huge files. If the partition size is 3GB, we'll make a 3GB
> > loop image and fill files into it. And I shrink the loop image to the
> > minimum size and flash it to my phone. When first booting, the system will
> > do resizing the partition to 3GB original size.
> 
> What I would recommend is to estimate how big the file system needs to
> doing a "du -s" over the directory that you want to preload onto the
> file system size, add say, 5% or so the file system metadata, and then
> create the file system that way.  If the file system is close enough
> to the right size, then resize2fs -M is much more likely to shrink the
> file system to its minimal size, and also reduce the file

/me wonders if the script I threw into the last patchbomb would help?
http://patchwork.ozlabs.org/patch/457482/

If you intend to write to the FS after it's been expanded into the target
device, you should turn journalling on /after/ the expand operation.

--D

> fragmentation that results from it.  (One of the better uses for using
> resize2fs to slightly shrink a file system was to make room for the
> LVM table at the end of the device, for example.  It's when you try to
> take, say, a 1TB file system and shrink to a few megabytes that
> resize2fs doesn't do a great job, because it really wasn't engineered
> for that use case, and it's hard enough to make sure it does so in a
> efficient and robust manner as it is.)
> 
> You can then take that file system and shrink to a size far larger
> than what it was originally created as --- that works much better than
> taking a large empty file system, shrinking it down to its minimal
> size, and then expanding it to something bigger.  If necessary, you
> can use the "mke2fs -E resize=15T" option to make sure enough metadata
> blocks have been reserved so the file system can be expanded as much
> as you would like.  By default we reserve enough metadata blocks for
> the file system to grow by a factor of a thousand, so if you create a
> super-tiny file system and then expect to grow it to a multi-TB size,
> that mke2fs option will be useful.  It's not strictly necessary for
> ext4 (although it was required for ext3), but it will result in a
> slightly more efficient file system that will mount more quickly under
> ext4.
> 
> So if your Tizen image is, say, 390 megabytes, I'd suggest creating a
> 400 megabyte file system, and load that up with the image.  If you
> then use resize2fs -M, it should shirnk it down to something much
> closer to 390M.
> 
> I suspect you will find that the resulting image will be far more
> efficient than trying to start with a 3GB file system, shrink it down
> to 400M, and then expand it backup to 3GB.
> 
> Best regards,
> 
> 					- Ted
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