linux-ext4 - Re: [PATCH] mke2fs: disable resize_inode feature if 64bit feature is enabled

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Date:	Tue, 4 Mar 2014 10:19:25 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Lukáš Czerner <lczerner@...hat.com>
Cc:	Eryu Guan <guaneryu@...il.com>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] mke2fs: disable resize_inode feature if 64bit feature is
 enabled

On Mon, Mar 03, 2014 at 04:40:21PM +0100, Lukáš Czerner wrote:
> 
> are you going to take this in ?
> 
> > It's better to use the resize_inode for file systems that are smaller
> > than 16TB, even if the 64-bit flag is enabled, since using the meta_bg
> > style resizing spreads out the block group descriptors, which
> > increases the time to mount the file system.  Using the resize_inode
> > will defer the need to go to the meta_bg-style resizing until we cross
> > the 16TB boundary.

See my comments above.

If we create a file system which is say, 1T but with the 64-bit flag,
we do want the resize_inode feature to be used until we cross over the
32-bit boundary, because keeping block group descriptors contiguous
speeds up the mount time.

If I were to accept this patch, and/or Red Hat were to ship with it, I
will predict that you will get angry customer support calls about file
system mount times getting slow after doing a resize.

At some point what we may want to lazily load the block group
descriptors at mount time, to mitigate the slow mount time issue when
using meta_bg.  We have a lot of assumptions in the code that the
block group descriptors are always available, though.

      	    		    	   	      - Ted
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