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    jbd: fix the way the b_modified flag is cleared · 5bc833fe
    Josef Bacik 提交于
    Currently at the start of a journal commit we loop through all of the buffers
    on the committing transaction and clear the b_modified flag (the flag that is
    set when a transaction modifies the buffer) under the j_list_lock.
    
    The problem is that everywhere else this flag is modified only under the jbd
    lock buffer flag, so it will race with a running transaction who could
    potentially set it, and have it unset by the committing transaction.
    
    This is also a big waste, you can have several thousands of buffers that you
    are clearing the modified flag on when you may not need to.  This patch
    removes this code and instead clears the b_modified flag upon entering
    do_get_write_access/journal_get_create_access, so if that transaction does
    indeed use the buffer then it will be accounted for properly, and if it does
    not then we know we didn't use it.
    
    That will be important for the next patch in this series.  Tested thoroughly
    by myself using postmark/iozone/bonnie++.
    Signed-off-by: NJosef Bacik <jbacik@redhat.com>
    Cc: <linux-ext4@vger.kernel.org>
    Acked-by: NJan Kara <jack@ucw.cz>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    5bc833fe
transaction.c 62.0 KB