High 'Creating block layer request' or '[sleep_on_page] ' latency

[Dongsheng Song]

Hi all,

I have observed many high 'Creating block layer request' or
'[sleep_on_page] ' latency on Linux 3.2.4 and btrfs.

Cause                           Maximum          Percentage
synchronous write               14590.0 msec          5.9 %
[btrfs_pin_log_trans]           12743.8 msec          7.8 %
[lock_rename]                    2624.6 msec          1.1 %
Creating a file                  1835.7 msec          3.2 %
Creating block layer request     1835.2 msec         53.8 %
Reading directory content        1674.0 msec          4.8 %
[sleep_on_page]                  1661.9 msec         21.0 %
Reading from file                1626.9 msec          2.2 %
Opening file                      118.7 msec          0.2 %

Cause                           Maximum         Percentage
Creating block layer request    3716.4 msec         55.1 %
[sleep_on_page]                  606.5 msec         27.7 %
Reading from file                571.9 msec          4.4 %
Page fault                       550.8 msec          6.8 %
Pagecache sync readahead         108.3 msec          0.2 %
synchronous write                103.0 msec          0.8 %
Creating a file                   88.3 msec          3.1 %
[btrfs_tree_lock]                 58.2 msec          0.1 %
[btrfs_pin_log_trans]             33.8 msec          0.1 %

Is there something wrong ?

Regards,
Dongsheng
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