• Herbert Xu's avatar
    rhashtable: Add cap on number of elements in hash table · 07ee0722
    Herbert Xu authored
    We currently have no limit on the number of elements in a hash table.
    This is a problem because some users (tipc) set a ceiling on the
    maximum table size and when that is reached the hash table may
    degenerate.  Others may encounter OOM when growing and if we allow
    insertions when that happens the hash table perofrmance may also
    suffer.
    
    This patch adds a new paramater insecure_max_entries which becomes
    the cap on the table.  If unset it defaults to max_size * 2.  If
    it is also zero it means that there is no cap on the number of
    elements in the table.  However, the table will grow whenever the
    utilisation hits 100% and if that growth fails, you will get ENOMEM
    on insertion.
    
    As allowing oversubscription is potentially dangerous, the name
    contains the word insecure.
    
    Note that the cap is not a hard limit.  This is done for performance
    reasons as enforcing a hard limit will result in use of atomic ops
    that are heavier than the ones we currently use.
    
    The reasoning is that we're only guarding against a gross over-
    subscription of the table, rather than a small breach of the limit.
    Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    07ee0722
rhashtable.h 24.8 KB