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Date:	Sun, 3 Apr 2011 21:07:43 +0300
From:	Zeev Tarantov <>
Subject: problem(?) in ext4 or mke2fs

While testing zram I ran a script that creates a block devices,
creates a filesystem on in and untars Qt on that filesystem.
I was surprised to find ext4_mb_scan_aligned near the top of the profile output.
This was evidently because the command "mke2fs -t ext4 -m 0 -I 128 -O
^has_journal,^ext_attr <block device>"
 created a filesystem with (output of tune2fs):
RAID stride:              1
RAID stripe width:        1

I thought this strange and removed these values using debugfs:
set_super_value raid_stride 0
set_super_value raid_stripe_width 0

With this "fix" the symbol ext4_mb_scan_aligned disappeared from perf's output:

    18.98%     -3.66%  gzip                            [.] zip
     0.00%    +14.84%  [kernel.kallsyms]               [k] ext4_mb_scan_aligned
    17.91%     -3.44%  gzip                            [.]
    13.73%     -2.47%  [csnappy_compress]              [k]
     3.96%     -0.77%  [kernel.kallsyms]               [k]
     3.05%     -0.41%                    [.] __memcpy_ssse3
     0.89%     +1.49%  [kernel.kallsyms]               [k] _raw_spin_lock
     2.63%     -0.49%  [kernel.kallsyms]               [k] __memcpy
     1.61%     -0.17%  [kernel.kallsyms]               [k] __memset
     0.78%     -0.11%  [kernel.kallsyms]               [k] ext4_mark_iloc_dirty
     0.63%     -0.11%  [kernel.kallsyms]               [k] system_call
     0.66%     -0.14%  gzip                            [.] treat_stdin.2262
     0.58%     -0.12%                    [.] _int_malloc

This is using mke2fs 1.41.14 (22-Dec-2010) on Linux

Is this expected behavior? Do you need me to provide more information?

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