• Dave Chinner's avatar
    xfs: Introduce ordered log vector support · fd63875c
    Dave Chinner authored
    And "ordered log vector" is a log vector that is used for
    tracking a log item through the CIL and into the AIL as part of the
    log checkpointing. These ordered log vectors are special in that
    they are not written to to journal in any way, and are not accounted
    to the checkpoint being written.
    
    The reason for this behaviour is to allow operations to attach items
    to transactions and have them follow the normal transactional
    lifecycle without actually having to write them to the journal. This
    allows logging of items that track high level logical changes and
    writing them to the log, while the physical items being modified
    pass through into the AIL and pin the tail of the log (and therefore
    the logical item in the log) until all the modified items are
    physically written to disk.
    
    IOWs, it allows us to write metadata without physically logging
    every individual change but still maintain the full transactional
    integrity guarantees we currently have w.r.t. crash recovery.
    
    This change modifies some of the CIL item insertion loops, as
    ordered log vectors introduce some new constraints as they don't
    track any data. One advantage of this change is that it combines
    two log vector chain walks into a single pass, so there is less
    overhead in the transaction commit pass as well. It also kills some
    unused code in the log vector walk loop when committing the CIL.
    Signed-off-by: default avatarDave Chinner <dchinner@redhat.com>
    Reviewed-by: default avatarMark Tinguely <tinguely@sgi.com>
    Signed-off-by: default avatarBen Myers <bpm@sgi.com>
    fd63875c
xfs_log.c 105 KB