linux-ext4 - bigalloc cluster size

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Date:	Tue, 21 Apr 2015 16:31:20 +0300
From:	Alexander Tsvetkov <alexander.tsvetkov@...cle.com>
To:	linux-ext4@...r.kernel.org
Subject: bigalloc cluster size

Hello,

I've noted that valid cluster size is not limited by 256M according to 
"mke2fs" manual:

"-C  cluster-size
Specify the size of cluster in bytes for filesystems using the bigalloc 
feature.  Valid cluster-size values are from 2048 to 256M bytes per 
cluster."

but actually it's limited by 512M:

"[root@...ora ~]# mkfs.ext4 -O bigalloc -C 512m /dev/sdb
mke2fs 1.43-WIP (29-Mar-2015)
/dev/sdb contains a ext4 file system
     created on Tue Apr 21 15:30:27 2015
Proceed anyway? (y,n) yes

Warning: the bigalloc feature is still under development
See https://ext4.wiki.kernel.org/index.php/Bigalloc for more information

Creating filesystem with 2097152 4k blocks and 16 inodes

Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

[root@...ora ~]# mkfs.ext4 -O bigalloc -C 1024m /dev/sdb
mkfs.ext4: invalid cluster size - 1024m"

(running on vbox Fedora x86_64, latest e2fsprogs, kernel 4.0.0-rc5)

Is it documentation issue?

Thanks,
Alexander Tsvetkov
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