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    xfs: bulk AIL insertion during transaction commit · 0e57f6a3
    Dave Chinner 提交于
    When inserting items into the AIL from the transaction committed
    callbacks, we take the AIL lock for every single item that is to be
    inserted. For a CIL checkpoint commit, this can be tens of thousands
    of individual inserts, yet almost all of the items will be inserted
    at the same point in the AIL because they have the same index.
    
    To reduce the overhead and contention on the AIL lock for such
    operations, introduce a "bulk insert" operation which allows a list
    of log items with the same LSN to be inserted in a single operation
    via a list splice. To do this, we need to pre-sort the log items
    being committed into a temporary list for insertion.
    
    The complexity is that not every log item will end up with the same
    LSN, and not every item is actually inserted into the AIL. Items
    that don't match the commit LSN will be inserted and unpinned as per
    the current one-at-a-time method (relatively rare), while items that
    are not to be inserted will be unpinned and freed immediately. Items
    that are to be inserted at the given commit lsn are placed in a
    temporary array and inserted into the AIL in bulk each time the
    array fills up.
    
    As a result of this, we trade off AIL hold time for a significant
    reduction in traffic. lock_stat output shows that the worst case
    hold time is unchanged, but contention from AIL inserts drops by an
    order of magnitude and the number of lock traversal decreases
    significantly.
    Signed-off-by: NDave Chinner <dchinner@redhat.com>
    Reviewed-by: NChristoph Hellwig <hch@lst.de>
    0e57f6a3
xfs_log_cil.c 24.3 KB