• Dave Chinner's avatar
    percpu_counter: batch size aware __percpu_counter_compare() · 80188b0d
    Dave Chinner authored
    XFS uses non-stanard batch sizes for avoiding frequent global
    counter updates on it's allocated inode counters, as they increment
    or decrement in batches of 64 inodes. Hence the standard percpu
    counter batch of 32 means that the counter is effectively a global
    counter. Currently Xfs uses a batch size of 128 so that it doesn't
    take the global lock on every single modification.
    However, Xfs also needs to compare accurately against zero, which
    means we need to use percpu_counter_compare(), and that has a
    hard-coded batch size of 32, and hence will spuriously fail to
    detect when it is supposed to use precise comparisons and hence
    the accounting goes wrong.
    Add __percpu_counter_compare() to take a custom batch size so we can
    use it sanely in XFS and factor percpu_counter_compare() to use it.
    Signed-off-by: default avatarDave Chinner <dchinner@redhat.com>
    Acked-by: default avatarTejun Heo <tj@kernel.org>
    Signed-off-by: default avatarDave Chinner <david@fromorbit.com>
percpu_counter.c 5.47 KB