• Daniel Borkmann's avatar
    rhashtable: unconditionally grow when max_shift is not specified · 8331de75
    Daniel Borkmann authored
    While commit c0c09bfd ("rhashtable: avoid unnecessary wakeup for
    worker queue") rightfully moved part of the decision making of
    whether we should expand or shrink from the expand/shrink functions
    themselves into insert/delete functions in order to avoid unnecessary
    worker wake-ups, it however introduced a regression by doing so.
    
    Before that change, if no max_shift was specified (= 0) on rhashtable
    initialization, rhashtable_expand() would just grow unconditionally
    and lets the available memory be the limiting factor. After that
    change, if no max_shift was specified, there would be _no_ expansion
    step at all.
    
    Given that netlink and tipc have a max_shift specified, it was not
    visible there, but Josh Hunt reported that if nft that starts out
    with a default element hint of 3 if not otherwise provided, would
    slow i.e. inserts down trememdously as it cannot grow larger to
    relax table occupancy.
    
    Given that the test case verifies shrinks/expands manually, we also
    must remove pointer to the helper functions to explicitly avoid
    parallel resizing on insertions/deletions. test_bucket_stats() and
    test_rht_lookup() could also be wrapped around rhashtable mutex to
    explicitly synchronize a walk from resizing, but I think that defeats
    the actual test case which intended to have explicit test steps,
    i.e. 1) inserts, 2) expands, 3) shrinks, 4) deletions, with object
    verification after each stage.
    Reported-by: default avatarJosh Hunt <johunt@akamai.com>
    Fixes: c0c09bfd ("rhashtable: avoid unnecessary wakeup for worker queue")
    Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
    Cc: Ying Xue <ying.xue@windriver.com>
    Cc: Josh Hunt <johunt@akamai.com>
    Acked-by: default avatarThomas Graf <tgraf@suug.ch>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    8331de75
test_rhashtable.c 4.99 KB