• Dave Chinner's avatar
    xfs: remove bitfield based superblock updates · 4d11a402
    Dave Chinner authored
    When we log changes to the superblock, we first have to write them
    to the on-disk buffer, and then log that. Right now we have a
    complex bitfield based arrangement to only write the modified field
    to the buffer before we log it.
    
    This used to be necessary as a performance optimisation because we
    logged the superblock buffer in every extent or inode allocation or
    freeing, and so performance was extremely important. We haven't done
    this for years, however, ever since the lazy superblock counters
    pulled the superblock logging out of the transaction commit
    fast path.
    
    Hence we have a bunch of complexity that is not necessary that makes
    writing the in-core superblock to disk much more complex than it
    needs to be. We only need to log the superblock now during
    management operations (e.g. during mount, unmount or quota control
    operations) so it is not a performance critical path anymore.
    
    As such, remove the complex field based logging mechanism and
    replace it with a simple conversion function similar to what we use
    for all other on-disk structures.
    
    This means we always log the entirity of the superblock, but again
    because we rarely modify the superblock this is not an issue for log
    bandwidth or CPU time. Indeed, if we do log the superblock
    frequently, delayed logging will minimise the impact of this
    overhead.
    
    [Fixed gquota/pquota inode sharing regression noticed by bfoster.]
    Signed-off-by: default avatarDave Chinner <dchinner@redhat.com>
    Reviewed-by: default avatarBrian Foster <bfoster@redhat.com>
    Signed-off-by: default avatarDave Chinner <david@fromorbit.com>
    4d11a402
xfs_qm.c 46.8 KB