• Theodore Ts'o's avatar
    ext4: Fix async commit mode to be safe by using a barrier · 19cc48e3
    Theodore Ts'o authored
    Previously the journal_async_commit mount option was equivalent to
    using barrier=0 (and just as unsafe).  This patch fixes it so that we
    eliminate the barrier before the commit block (by not using ordered
    mode), and explicitly issuing an empty barrier bio after writing the
    commit block.  Because of the journal checksum, it is safe to do this;
    if the journal blocks are not all written before a power failure, the
    checksum in the commit block will prevent the last transaction from
    being replayed.
    
    Using the fs_mark benchmark, using journal_async_commit shows a 50%
    improvement:
    
    FSUse%        Count         Size    Files/sec     App Overhead
         8         1000        10240         30.5            28242
    
    vs.
    
    FSUse%        Count         Size    Files/sec     App Overhead
         8         1000        10240         45.8            28620
    Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
    19cc48e3
commit.c 32.2 KB