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

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Message-ID: <alpine.LFD.2.00.1403061458340.2249@localhost.localdomain>
Date:	Thu, 6 Mar 2014 15:03:30 +0100 (CET)
From:	Lukáš Czerner <lczerner@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
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 Tue, 4 Mar 2014, Theodore Ts'o wrote:

> 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

Hi Ted,

I am sorry, but am I missing something ? This patch seems to do
exactly that.

	if ((fs_blocks_count > MAX_32_NUM) &&
+	    (fs_param.s_feature_incompat & EXT4_FEATURE_INCOMPAT_64BIT))
+		fs_param.s_feature_compat &= ~EXT2_FEATURE_COMPAT_RESIZE_INODE;

The answer from you on that patch is commenting on a guestion from
Zheng Liu who is asking whether we could skip the MAX_32_NUM check.

So the patch seems to be ok for me.

Thanks!
-Lukas