• Johannes Weiner's avatar
    net: tcp_memcontrol: sanitize tcp memory accounting callbacks · e805605c
    Johannes Weiner authored
    There won't be a tcp control soft limit, so integrating the memcg code
    into the global skmem limiting scheme complicates things unnecessarily.
    Replace this with simple and clear charge and uncharge calls--hidden
    behind a jump label--to account skb memory.
    
    Note that this is not purely aesthetic: as a result of shoehorning the
    per-memcg code into the same memory accounting functions that handle the
    global level, the old code would compare the per-memcg consumption
    against the smaller of the per-memcg limit and the global limit.  This
    allowed the total consumption of multiple sockets to exceed the global
    limit, as long as the individual sockets stayed within bounds.  After
    this change, the code will always compare the per-memcg consumption to
    the per-memcg limit, and the global consumption to the global limit, and
    thus close this loophole.
    
    Without a soft limit, the per-memcg memory pressure state in sockets is
    generally questionable.  However, we did it until now, so we continue to
    enter it when the hard limit is hit, and packets are dropped, to let
    other sockets in the cgroup know that they shouldn't grow their transmit
    windows, either.  However, keep it simple in the new callback model and
    leave memory pressure lazily when the next packet is accepted (as
    opposed to doing it synchroneously when packets are processed).  When
    packets are dropped, network performance will already be in the toilet,
    so that should be a reasonable trade-off.
    
    As described above, consumption is now checked on the per-memcg level
    and the global level separately.  Likewise, memory pressure states are
    maintained on both the per-memcg level and the global level, and a
    socket is considered under pressure when either level asserts as much.
    Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
    Reviewed-by: default avatarVladimir Davydov <vdavydov@virtuozzo.com>
    Acked-by: default avatarDavid S. Miller <davem@davemloft.net>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    e805605c
tcp.h 54.4 KB