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    Btrfs: introduce qgroup_ulist to avoid frequently allocating/freeing ulist · 1e8f9158
    Wang Shilong 提交于
    When doing qgroup accounting, we call ulist_alloc()/ulist_free() every time
    when we want to walk qgroup tree.
    
    By introducing 'qgroup_ulist', we only need to call ulist_alloc()/ulist_free()
    once. This reduce some sys time to allocate memory, see the measurements below
    
    fsstress -p 4 -n 10000 -d $dir
    
    With this patch:
    
    real    0m50.153s
    user    0m0.081s
    sys     0m6.294s
    
    real    0m51.113s
    user    0m0.092s
    sys     0m6.220s
    
    real    0m52.610s
    user    0m0.096s
    sys     0m6.125s	avg 6.213
    -----------------------------------------------------
    Without the patch:
    
    real    0m54.825s
    user    0m0.061s
    sys     0m10.665s
    
    real    1m6.401s
    user    0m0.089s
    sys     0m11.218s
    
    real    1m13.768s
    user    0m0.087s
    sys     0m10.665s       avg 10.849
    
    we can see the sys time reduce ~43%.
    Signed-off-by: NWang Shilong <wangsl-fnst@cn.fujitsu.com>
    Signed-off-by: NJosef Bacik <jbacik@fusionio.com>
    1e8f9158
disk-io.c 108.2 KB