1. 20 Sep, 2017 1 commit
    • Jesper Dangaard Brouer's avatar
      Revert "net: use lib/percpu_counter API for fragmentation mem accounting" · 021c60ff
      Jesper Dangaard Brouer authored
      
      [ Upstream commit fb452a1a ]
      
      This reverts commit 6d7b857d.
      
      There is a bug in fragmentation codes use of the percpu_counter API,
      that can cause issues on systems with many CPUs.
      
      The frag_mem_limit() just reads the global counter (fbc->count),
      without considering other CPUs can have upto batch size (130K) that
      haven't been subtracted yet.  Due to the 3MBytes lower thresh limit,
      this become dangerous at >=24 CPUs (3*1024*1024/130000=24).
      
      The correct API usage would be to use __percpu_counter_compare() which
      does the right thing, and takes into account the number of (online)
      CPUs and batch size, to account for this and call __percpu_counter_sum()
      when needed.
      
      We choose to revert the use of the lib/percpu_counter API for frag
      memory accounting for several reasons:
      
      1) On systems with CPUs > 24, the heavier fully locked
         __percpu_counter_sum() is always invoked, which will be more
         expensive than the atomic_t that is reverted to.
      
      Given systems with more than 24 CPUs are becoming common this doesn't
      seem like a good option.  To mitigate this, the batch size could be
      decreased and thresh be increased.
      
      2) The add_frag_mem_limit+sub_frag_mem_limit pairs happen on the RX
         CPU, before SKBs are pushed into sockets on remote CPUs.  Given
         NICs can only hash on L2 part of the IP-header, the NIC-RXq's will
         likely be limited.  Thus, a fair chance that atomic add+dec happen
         on the same CPU.
      
      Revert note that commit 1d6119ba ("net: fix percpu memory leaks")
      removed init_frag_mem_limit() and instead use inet_frags_init_net().
      After this revert, inet_frags_uninit_net() becomes empty.
      
      Fixes: 6d7b857d ("net: use lib/percpu_counter API for fragmentation mem accounting")
      Fixes: 1d6119ba ("net: fix percpu memory leaks")
      Signed-off-by: default avatarJesper Dangaard Brouer <brouer@redhat.com>
      Acked-by: default avatarFlorian Westphal <fw@strlen.de>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      021c60ff
  2. 13 Sep, 2017 29 commits
  3. 10 Sep, 2017 1 commit
  4. 09 Sep, 2017 9 commits