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    ext4: limit the length of per-inode prealloc list · 27bc446e
    brookxu authored
    In the scenario of writing sparse files, the per-inode prealloc list may
    be very long, resulting in high overhead for ext4_mb_use_preallocated().
    To circumvent this problem, we limit the maximum length of per-inode
    prealloc list to 512 and allow users to modify it.
    
    After patching, we observed that the sys ratio of cpu has dropped, and
    the system throughput has increased significantly. We created a process
    to write the sparse file, and the running time of the process on the
    fixed kernel was significantly reduced, as follows:
    
    Running time on unfixed kernel:
    [root@TENCENT64 ~]# time taskset 0x01 ./sparse /data1/sparce.dat
    real    0m2.051s
    user    0m0.008s
    sys     0m2.026s
    
    Running time on fixed kernel:
    [root@TENCENT64 ~]# time taskset 0x01 ./sparse /data1/sparce.dat
    real    0m0.471s
    user    0m0.004s
    sys     0m0.395s
    Signed-off-by: default avatarChunguang Xu <brookxu@tencent.com>
    Link: https://lore.kernel.org/r/d7a98178-056b-6db5-6bce-4ead23f4a257@gmail.comSigned-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
    27bc446e
super.c 182 KB