Fwd: Far too long mount time

Fwd: Far too long mount time

[Javier Marcet]

Hi,

I'm in the process of setting up a new software raid with four 3TB disks.
So far I'm doing the tests using also bcache on a 60GB partition on a 120GB
SSD. Everything is protected by a UPS.

On the software side: self compiled kernel 3.5.1 and util-linux 2.20.1

Thus far, ext4 is doing really really well but for one thing, the mount
time. At the
moment I'm testing a RAID5 which makes the partition 8.2TB.

ext4 takes:
$ time mount /mnt/raid
0.00s user 79.49s system 92% cpu 1:26.25 total

xfs, OTOH, is way faster:
time mount /mnt/raid
0.00s user 0.01s system 0% cpu 1.869 total

I'v tried everything I could think of but the mount time remains constant.
Is
there anything I can do to speed up the mount time?


--
Javier Marcet <jmarcet@gmail.com>

Re: Far too long mount time

[Andreas Dilger]

On 2012-08-16, at 1:54 AM, Javier Marcet wrote:
> I'm in the process of setting up a new software raid with four 3TB disks.
> So far I'm doing the tests using also bcache on a 60GB partition on a 120GB
> SSD. Everything is protected by a UPS.
> 
> On the software side: self compiled kernel 3.5.1 and util-linux 2.20.1
> 
> Thus far, ext4 is doing really really well but for one thing, the mount
> time. At the moment I'm testing a RAID5 which makes the partition 8.2TB.
> 
> ext4 takes:
> $ time mount /mnt/raid
> 0.00s user 79.49s system 92% cpu 1:26.25 total
> 
> xfs, OTOH, is way faster:
> time mount /mnt/raid
> 0.00s user 0.01s system 0% cpu 1.869 total
> 
> I'v tried everything I could think of but the mount time remains constant.
> Is there anything I can do to speed up the mount time?

Did you format the filesystem with "mke2fs -t ext4"?  Without the "-t ext4" option, you won't get the "flex_bg" formatting option, which improves the layout of the filesystem metadata, and definitely reduces mount times.

It is a bit strange that _mounting_ uses 92% CPU.  Hmm, there was a bug
reported for 3.5.1, see "Re: Upgraded from 3.4 to 3.5.1 kernel: machine
does not boot", and reverting the patch with git commit hash
"8aeb00ff85ad25453765dd339b408c0087db1527" resolved the problem.  This
slowdown was only seen with larger devices.

Cheers, Andreas

Re: Far too long mount time

[Javier Marcet]

On Thu, Aug 16, 2012 at 11:09 AM, Andreas Dilger <adilger@dilger.ca> wrote:

>> I'm in the process of setting up a new software raid with four 3TB disks.
>> So far I'm doing the tests using also bcache on a 60GB partition on a 120GB
>> SSD. Everything is protected by a UPS.
>>
>> On the software side: self compiled kernel 3.5.1 and util-linux 2.20.1
>>
>> Thus far, ext4 is doing really really well but for one thing, the mount
>> time. At the moment I'm testing a RAID5 which makes the partition 8.2TB.
>>
>> ext4 takes:
>> $ time mount /mnt/raid
>> 0.00s user 79.49s system 92% cpu 1:26.25 total
>>
>> xfs, OTOH, is way faster:
>> time mount /mnt/raid
>> 0.00s user 0.01s system 0% cpu 1.869 total
>>
>> I'v tried everything I could think of but the mount time remains constant.
>> Is there anything I can do to speed up the mount time?
>
> Did you format the filesystem with "mke2fs -t ext4"?  Without the "-t ext4" option, you won't get the "flex_bg" formatting option, which improves the layout of the filesystem metadata, and definitely reduces mount times.

Hmm, I used mkfs.ext4. Loooking at /etc/mke2fs.conf :

defaults]
        base_features = sparse_super,filetype,resize_inode,dir_index,ext_attr
        default_mntopts = acl,user_xattr
        enable_periodic_fsck = 0
        blocksize = 4096
        inode_size = 256
        inode_ratio = 16384

[fs_types]
        ext3 = {
                features = has_journal
        }
        ext4 = {
                features =
has_journal,extent,huge_file,flex_bg,uninit_bg,dir_nlink,extra_isize
                auto_64-bit_support = 1
                inode_size = 256
        }

It looks like flex_bg is being used.

> It is a bit strange that _mounting_ uses 92% CPU.  Hmm, there was a bug
> reported for 3.5.1, see "Re: Upgraded from 3.4 to 3.5.1 kernel: machine

That also surprised me. At first I thought it was bcache, but with zfs the
behavior is normal.

> does not boot", and reverting the patch with git commit hash
> "8aeb00ff85ad25453765dd339b408c0087db1527" resolved the problem.  This
> slowdown was only seen with larger devices.

I'll check it right now.

I've reverted it and I'm compiling the new kernel. I'll keep you
posted on the results.

By the way, when you say larger, you mean much larger than 8TB?


-- 
Javier Marcet <jmarcet@gmail.com>

Re: Far too long mount time

[Javier Marcet]

On Thu, Aug 16, 2012 at 11:09 AM, Andreas Dilger <adilger@dilger.ca> wrote:

> It is a bit strange that _mounting_ uses 92% CPU.  Hmm, there was a bug
> reported for 3.5.1, see "Re: Upgraded from 3.4 to 3.5.1 kernel: machine
> does not boot", and reverting the patch with git commit hash
> "8aeb00ff85ad25453765dd339b408c0087db1527" resolved the problem.  This
> slowdown was only seen with larger devices.

Thanks a lot Andreas, that commit was the cause. Reverting it:

$ time mount /mnt/raid
0.00s user 0.03s system 5% cpu 0.511 total


-- 
Javier Marcet <jmarcet@gmail.com>

Re: Far too long mount time

[Calvin Walton]

On Thu, 2012-08-16 at 03:09 -0600, Andreas Dilger wrote:
> On 2012-08-16, at 1:54 AM, Javier Marcet wrote:
> > I'm in the process of setting up a new software raid with four 3TB disks.
> > So far I'm doing the tests using also bcache on a 60GB partition on a 120GB
> > SSD. Everything is protected by a UPS.
> > 
> > On the software side: self compiled kernel 3.5.1 and util-linux 2.20.1
> > 
> > Thus far, ext4 is doing really really well but for one thing, the mount
> > time. At the moment I'm testing a RAID5 which makes the partition 8.2TB.
> > 
> > ext4 takes:
> > $ time mount /mnt/raid
> > 0.00s user 79.49s system 92% cpu 1:26.25 total

> It is a bit strange that _mounting_ uses 92% CPU.  Hmm, there was a bug
> reported for 3.5.1, see "Re: Upgraded from 3.4 to 3.5.1 kernel: machine
> does not boot", and reverting the patch with git commit hash
> "8aeb00ff85ad25453765dd339b408c0087db1527" resolved the problem.  This
> slowdown was only seen with larger devices.

I've been seeing this as well, the symptom being the boot time on my
computer going from <5s to ~20s while my 6TB ext4 filesystem mounts.
I'll try reverting this patch; hopefully that helps.

Is there any fix for this issue queued up for an upcoming stable
release? It still reverts cleanly on 3.5.2.

-- 
Calvin Walton <calvin.walton@kepstin.ca>

Re: Far too long mount time

[Theodore Ts'o]

On Thu, Aug 16, 2012 at 10:16:48AM -0400, Calvin Walton wrote:
> On Thu, 2012-08-16 at 03:09 -0600, Andreas Dilger wrote:
> Is there any fix for this issue queued up for an upcoming stable
> release? It still reverts cleanly on 3.5.2.

There isn't a fix queued up yet, but there will be one soon....

					- Ted

Re: Far too long mount time

[Theodore Ts'o]

On Thu, Aug 16, 2012 at 10:42:19AM -0400, Theodore Ts'o wrote:
> On Thu, Aug 16, 2012 at 10:16:48AM -0400, Calvin Walton wrote:
> > On Thu, 2012-08-16 at 03:09 -0600, Andreas Dilger wrote:
> > Is there any fix for this issue queued up for an upcoming stable
> > release? It still reverts cleanly on 3.5.2.
> 
> There isn't a fix queued up yet, but there will be one soon....

This patch should solve the problem (as an alternative to reverting
8aeb00ff85a).

						- Ted


>From dc43c7a8a6c266c31aa4f0408000c4d1b9f3c787 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@mit.edu>
Date: Thu, 16 Aug 2012 11:59:04 -0400
Subject: [PATCH] ext4: fix long mount times on very big file systems

Commit 8aeb00ff85a: "ext4: fix overhead calculation used by
ext4_statfs()" introduced a O(n**2) calculation which makes very large
file systems take forever to mount.  Fix this with an optimization for
non-bigalloc file systems.  (For bigalloc file systems the overhead
needs to be set in the the superblock.)

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org
---
 fs/ext4/super.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 603023b..055c65b 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3129,6 +3129,10 @@ static int count_overhead(struct super_block *sb, ext4_group_t grp,
 	ext4_group_t		i, ngroups = ext4_get_groups_count(sb);
 	int			s, j, count = 0;
 
+	if (!EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_BIGALLOC))
+		return (ext4_bg_has_super(sb, grp) + ext4_bg_num_gdb(sb, i) +
+			sbi->s_itb_per_group + 2);
+
 	first_block = le32_to_cpu(sbi->s_es->s_first_data_block) +
 		(grp * EXT4_BLOCKS_PER_GROUP(sb));
 	last_block = first_block + EXT4_BLOCKS_PER_GROUP(sb) - 1;
-- 
1.7.12.rc0.22.gcdd159b

Re: Far too long mount time

[Eric Sandeen]

On 8/16/12 1:53 PM, Theodore Ts'o wrote:
> On Thu, Aug 16, 2012 at 10:42:19AM -0400, Theodore Ts'o wrote:
>> On Thu, Aug 16, 2012 at 10:16:48AM -0400, Calvin Walton wrote:
>>> On Thu, 2012-08-16 at 03:09 -0600, Andreas Dilger wrote:
>>> Is there any fix for this issue queued up for an upcoming stable
>>> release? It still reverts cleanly on 3.5.2.
>>
>> There isn't a fix queued up yet, but there will be one soon....
>
> This patch should solve the problem (as an alternative to reverting
> 8aeb00ff85a).
>
> 						- Ted
>
>
>  From dc43c7a8a6c266c31aa4f0408000c4d1b9f3c787 Mon Sep 17 00:00:00 2001
> From: Theodore Ts'o <tytso@mit.edu>
> Date: Thu, 16 Aug 2012 11:59:04 -0400
> Subject: [PATCH] ext4: fix long mount times on very big file systems
>
> Commit 8aeb00ff85a: "ext4: fix overhead calculation used by
> ext4_statfs()" introduced a O(n**2) calculation which makes very large
> file systems take forever to mount.  Fix this with an optimization for
> non-bigalloc file systems.  (For bigalloc file systems the overhead
> needs to be set in the the superblock.)

And mkfs with bigalloc will do that, right?

Hm.
         /*
          * Get the # of file system overhead blocks from the
          * superblock if present.
          */
         if (es->s_overhead_clusters)
                 sbi->s_overhead = le32_to_cpu(es->s_overhead_clusters);
         else {
                 ret = ext4_calculate_overhead(sb);
                 if (ret)
                         goto failed_mount_wq;
         }

so if we mkfs'd with bigalloc, s_overhead_clusters will be set and we 
won't call ext4_calculate_overhead, right?

But if we didn't mkfs with bigalloc, we won't have the feature, and
ext4_calc_overhead will exit early.

So when does all of the code after the short-circuit ever run?

-Eric

> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
> Cc: stable@vger.kernel.org
> ---
>   fs/ext4/super.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 603023b..055c65b 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3129,6 +3129,10 @@ static int count_overhead(struct super_block *sb, ext4_group_t grp,
>   	ext4_group_t		i, ngroups = ext4_get_groups_count(sb);
>   	int			s, j, count = 0;
>
> +	if (!EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_BIGALLOC))
> +		return (ext4_bg_has_super(sb, grp) + ext4_bg_num_gdb(sb, i) +
> +			sbi->s_itb_per_group + 2);
> +
>   	first_block = le32_to_cpu(sbi->s_es->s_first_data_block) +
>   		(grp * EXT4_BLOCKS_PER_GROUP(sb));
>   	last_block = first_block + EXT4_BLOCKS_PER_GROUP(sb) - 1;
>

Re: Far too long mount time

[Theodore Ts'o]

On Thu, Aug 16, 2012 at 02:23:37PM -0500, Eric Sandeen wrote:
> 
> And mkfs with bigalloc will do that, right?

Not yet.

We also need to make sure s_overhead_clusters gets updated after a
resize operation, but I wanted to get a fix for non-bigalloc file
systems out there as soon as possible.

> So when does all of the code after the short-circuit ever run?

Until we get ths rest of the code fixed up, it will needed for all
bigalloc file systems.  The one saving grace is that bigalloc file
systems will have fewer block groups, so the O(n**2) won't be as bad
--- but it is something we really should fix.

					- Ted

Re: Far too long mount time

[Theodore Ts'o]

On Thu, Aug 16, 2012 at 02:53:37PM -0400, Theodore Ts'o wrote:
> This patch should solve the problem (as an alternative to reverting
> 8aeb00ff85a).
> 
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 603023b..055c65b 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3129,6 +3129,10 @@ static int count_overhead(struct super_block *sb, ext4_group_t grp,
>  	ext4_group_t		i, ngroups = ext4_get_groups_count(sb);
>  	int			s, j, count = 0;
>  
> +	if (!EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_BIGALLOC))
> +		return (ext4_bg_has_super(sb, grp) + ext4_bg_num_gdb(sb, i) +
                                                                        ^^^

This should be "grp"; stupid typo on my part.

This patch with the fix-up will be pushed to Linus shortly and tagged
for the stable tree.

     	       	      	     	     	- Ted

RE: Far too long mount time

[Justin Piszcz]

-----Original Message-----
From: Theodore Ts'o [mailto:tytso@mit.edu] 
Sent: Friday, August 17, 2012 9:55 AM
To: Calvin Walton
Cc: Andreas Dilger; Javier Marcet; Linux Ext4 Mailing List;
jpiszcz@lucidpixels.com
Subject: Re: Far too long mount time

On Thu, Aug 16, 2012 at 02:53:37PM -0400, Theodore Ts'o wrote:
> This patch should solve the problem (as an alternative to reverting
> 8aeb00ff85a).

This should be "grp"; stupid typo on my part.

This patch with the fix-up will be pushed to Linus shortly and tagged
for the stable tree.

--

Hi Theo,

Found the patch here:
http://www.spinics.net/lists/linux-ext4/msg33498.html

Patched against the fresh+stable 3.5.1 tree:

p34:/usr/src/linux-3.5.1# patch -p1 < ../tso.patch
patching file fs/ext4/super.c
Hunk #1 succeeded at 3109 (offset -20 lines).
p34:/usr/src/linux-3.5.1#

Rebooted, but we have a problem, my 60TB RAID-6 is now a 46TB RAID-6?
I am rebooting back into the 3.5.1+earlier reverted patch.

p34:~# uptime; uname -a ; df -h | grep /r1
 10:46:51 up 0 min,  1 user,  load average: 1.04, 0.27, 0.09
Linux p34 3.5.1 #5 SMP Fri Aug 17 10:24:22 EDT 2012 x86_64 GNU/Linux
/dev/sda1        46T  1.5T   45T   4% /r1
p34:~#

Justin.

Re: Far too long mount time

[Theodore Ts'o]

I'm confused; I didn't see your original message.  Your complaint was
with my buggy patch at:

   http://www.spinics.net/lists/linux-ext4/msg33498.html

without the s/i/grp/ fix applied, right?

						- Ted

RE: Far too long mount time

[Justin Piszcz]

-----Original Message-----
From: Justin Piszcz [mailto:jpiszcz@lucidpixels.com] 
Sent: Friday, August 17, 2012 10:48 AM
To: 'Theodore Ts'o'; 'Calvin Walton'; ap@solarrain.com
Cc: 'Andreas Dilger'; 'Javier Marcet'; 'Linux Ext4 Mailing List'
Subject: RE: Far too long mount time



-----Original Message-----
From: Theodore Ts'o [mailto:tytso@mit.edu] 
Sent: Friday, August 17, 2012 9:55 AM
To: Calvin Walton
Cc: Andreas Dilger; Javier Marcet; Linux Ext4 Mailing List;
jpiszcz@lucidpixels.com
Subject: Re: Far too long mount time

On Thu, Aug 16, 2012 at 02:53:37PM -0400, Theodore Ts'o wrote:
> This patch should solve the problem (as an alternative to reverting
> 8aeb00ff85a).

This should be "grp"; stupid typo on my part.

This patch with the fix-up will be pushed to Linus shortly and tagged
for the stable tree.

--

Hi Theo,

Found the patch here:
http://www.spinics.net/lists/linux-ext4/msg33498.html

Patched against the fresh+stable 3.5.1 tree:

p34:/usr/src/linux-3.5.1# patch -p1 < ../tso.patch
patching file fs/ext4/super.c
Hunk #1 succeeded at 3109 (offset -20 lines).
p34:/usr/src/linux-3.5.1#

Rebooted, but we have a problem, my 60TB RAID-6 is now a 46TB RAID-6?
I am rebooting back into the 3.5.1+earlier reverted patch.

p34:~# uptime; uname -a ; df -h | grep /r1
 10:46:51 up 0 min,  1 user,  load average: 1.04, 0.27, 0.09
Linux p34 3.5.1 #5 SMP Fri Aug 17 10:24:22 EDT 2012 x86_64 GNU/Linux
/dev/sda1        46T  1.5T   45T   4% /r1
p34:~#
--

Went back to old kernel (w/reverted patch, it is ok now)

p34:~# uname -a; uptime; df -h |grep /r1
Linux p34 3.5.1+ #3 SMP Sun Aug 12 10:31:34 EDT 2012 x86_64 GNU/Linux
 10:59:51 up 9 min,  1 user,  load average: 0.00, 0.20, 0.23
/dev/sda1        61T   16T   45T  27% /r1
p34:~#

Justin.

Re: Far too long mount time

[Theodore Ts'o]

On Fri, Aug 17, 2012 at 11:00:19AM -0400, Justin Piszcz wrote:
> 
> 
> -----Original Message-----
> From: Justin Piszcz [mailto:jpiszcz@lucidpixels.com] 
> Sent: Friday, August 17, 2012 10:48 AM
> To: 'Theodore Ts'o'; 'Calvin Walton'; ap@solarrain.com
> Cc: 'Andreas Dilger'; 'Javier Marcet'; 'Linux Ext4 Mailing List'
> Subject: RE: Far too long mount time
> 
> 
> 
> -----Original Message-----
> From: Theodore Ts'o [mailto:tytso@mit.edu] 
> Sent: Friday, August 17, 2012 9:55 AM
> To: Calvin Walton
> Cc: Andreas Dilger; Javier Marcet; Linux Ext4 Mailing List;
> jpiszcz@lucidpixels.com
> Subject: Re: Far too long mount time

I think there's something wrong with your mailer?  You just forwarded
your original message without any further additional text? 

Still confused,

     	      	      	      	  	  - Ted

Re: Far too long mount time

[Theodore Ts'o]

OK, I think what you were trying to say; that you've only gone back to
the original kernel and you have not tried the fixed patch.  Yes?

Sorry, all of the excess quoting made it very hard for me to parse
your reply....

						- Ted

RE: Far too long mount time

[Justin Piszcz]

-----Original Message-----
From: Theodore Ts'o [mailto:tytso@mit.edu] 
Sent: Friday, August 17, 2012 11:28 AM
To: Justin Piszcz
Cc: 'Calvin Walton'; ap@solarrain.com; 'Andreas Dilger'; 'Javier Marcet';
'Linux Ext4 Mailing List'
Subject: Re: Far too long mount time

OK, I think what you were trying to say; that you've only gone back to
the original kernel and you have not tried the fixed patch.  Yes?

Sorry, all of the excess quoting made it very hard for me to parse
your reply....

						- Ted


Hi Theo,

I used the patch from this URL:
http://www.spinics.net/lists/linux-ext4/msg33498.html

The filesystem does mount quickly and normally BUT it shows up as 45TB and
not the 60TB it is normally.
I went back to the 3.5.1 kernel with 8aeb00ff85a reverted and all is back to
normal.

Justin.

Re: Far too long mount time

[Eric Sandeen]

On 8/17/12 2:18 PM, Justin Piszcz wrote:
>
>
> -----Original Message-----
> From: Theodore Ts'o [mailto:tytso@mit.edu]
> Sent: Friday, August 17, 2012 11:28 AM
> To: Justin Piszcz
> Cc: 'Calvin Walton'; ap@solarrain.com; 'Andreas Dilger'; 'Javier Marcet';
> 'Linux Ext4 Mailing List'
> Subject: Re: Far too long mount time
>
> OK, I think what you were trying to say; that you've only gone back to
> the original kernel and you have not tried the fixed patch.  Yes?
>
> Sorry, all of the excess quoting made it very hard for me to parse
> your reply....
>
> 						- Ted
>
>
> Hi Theo,
>
> I used the patch from this URL:
> http://www.spinics.net/lists/linux-ext4/msg33498.html
>
> The filesystem does mount quickly and normally BUT it shows up as 45TB and
> not the 60TB it is normally.
> I went back to the 3.5.1 kernel with 8aeb00ff85a reverted and all is back to
> normal.

Didn't this all start w/ df reporting issues?  Seems like we need an xfs 
test explicitly for extN, with and without minixdf ....

-Eric

Re: Far too long mount time

[Andreas Dilger]

On 2012-08-16, at 12:53, Theodore Ts'o <tytso@mit.edu> wrote:
> On Thu, Aug 16, 2012 at 10:42:19AM -0400, Theodore Ts'o wrote:
>> On Thu, Aug 16, 2012 at 10:16:48AM -0400, Calvin Walton wrote:
>>> On Thu, 2012-08-16 at 03:09 -0600, Andreas Dilger wrote:
>>> Is there any fix for this issue queued up for an upcoming stable
>>> release? It still reverts cleanly on 3.5.2.
>> 
>> There isn't a fix queued up yet, but there will be one soon....
> 
> This patch should solve the problem (as an alternative to reverting
> 8aeb00ff85a).

Why not save the newly calculated value for s_oberhead_blocks to disk after the first time it is calculated?  The only time it would need to be changed again is after a resize operation, which could be done by calling count_overhead() at the end again. 

Cheers, Andreas

> From dc43c7a8a6c266c31aa4f0408000c4d1b9f3c787 Mon Sep 17 00:00:00 2001
> From: Theodore Ts'o <tytso@mit.edu>
> Date: Thu, 16 Aug 2012 11:59:04 -0400
> Subject: [PATCH] ext4: fix long mount times on very big file systems
> 
> Commit 8aeb00ff85a: "ext4: fix overhead calculation used by
> ext4_statfs()" introduced a O(n**2) calculation which makes very large
> file systems take forever to mount.  Fix this with an optimization for
> non-bigalloc file systems.  (For bigalloc file systems the overhead
> needs to be set in the the superblock.)
> 
> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
> Cc: stable@vger.kernel.org
> ---
> fs/ext4/super.c | 4 ++++
> 1 file changed, 4 insertions(+)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 603023b..055c65b 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3129,6 +3129,10 @@ static int count_overhead(struct super_block *sb, ext4_group_t grp,
>    ext4_group_t        i, ngroups = ext4_get_groups_count(sb);
>    int            s, j, count = 0;
> 
> +    if (!EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_BIGALLOC))
> +        return (ext4_bg_has_super(sb, grp) + ext4_bg_num_gdb(sb, i) +
> +            sbi->s_itb_per_group + 2);
> +
>    first_block = le32_to_cpu(sbi->s_es->s_first_data_block) +
>        (grp * EXT4_BLOCKS_PER_GROUP(sb));
>    last_block = first_block + EXT4_BLOCKS_PER_GROUP(sb) - 1;
> -- 
> 1.7.12.rc0.22.gcdd159b
>