• Javier González's avatar
    lightnvm: pblk: enable 1 LUN configuration · 21d22871
    Javier González authored
    Metadata I/Os are scheduled to minimize their impact on user data I/Os.
    When there are enough LUNs instantiated (i.e., enough bandwidth), it is
    easy to interleave metadata and data one after the other so that
    metadata I/Os are the ones being blocked and not vice-versa.
    
    We do this by calculating the distance between the I/Os in terms of the
    LUNs that are not in used, and selecting a free LUN that satisfies a
    the simple heuristic that metadata is scheduled behind. The per-LUN
    semaphores guarantee consistency. This works fine on >1 LUN
    configuration. However, when a single LUN is instantiated, this design
    leads to a deadlock, where metadata waits to be scheduled on a free LUN.
    
    This patch implements the 1 LUN case by simply scheduling the metadada
    I/O after the data I/O. In the process, we refactor the way a line is
    replaced to ensure that metadata writes are submitted after data writes
    in order to guarantee block sequentiality. Note that, since there is
    only one LUN, both I/Os will block each other by design. However, such
    configuration only pursues tight read latencies, not write bandwidth.
    Signed-off-by: default avatarJavier González <javier@cnexlabs.com>
    Signed-off-by: default avatarMatias Bjørling <m@bjorling.me>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    21d22871
pblk-map.c 4.93 KB