• Thomas Graf's avatar
    rhashtable: Per bucket locks & deferred expansion/shrinking · 97defe1e
    Thomas Graf authored
    Introduces an array of spinlocks to protect bucket mutations. The number
    of spinlocks per CPU is configurable and selected based on the hash of
    the bucket. This allows for parallel insertions and removals of entries
    which do not share a lock.
    
    The patch also defers expansion and shrinking to a worker queue which
    allows insertion and removal from atomic context. Insertions and
    deletions may occur in parallel to it and are only held up briefly
    while the particular bucket is linked or unzipped.
    
    Mutations of the bucket table pointer is protected by a new mutex, read
    access is RCU protected.
    
    In the event of an expansion or shrinking, the new bucket table allocated
    is exposed as a so called future table as soon as the resize process
    starts.  Lookups, deletions, and insertions will briefly use both tables.
    The future table becomes the main table after an RCU grace period and
    initial linking of the old to the new table was performed. Optimization
    of the chains to make use of the new number of buckets follows only the
    new table is in use.
    
    The side effect of this is that during that RCU grace period, a bucket
    traversal using any rht_for_each() variant on the main table will not see
    any insertions performed during the RCU grace period which would at that
    point land in the future table. The lookup will see them as it searches
    both tables if needed.
    
    Having multiple insertions and removals occur in parallel requires nelems
    to become an atomic counter.
    Signed-off-by: default avatarThomas Graf <tgraf@suug.ch>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    97defe1e
rhashtable.h 9.96 KB