udp: optimize bind(0) if many ports are in use
commit 9088c560 (udp: Improve port randomization) introduced a regression for UDP bind() syscall to null port (getting a random port) in case lot of ports are already in use. This is because we do about 28000 scans of very long chains (220 sockets per chain), with many spin_lock_bh()/spin_unlock_bh() calls. Fix this using a bitmap (64 bytes for current value of UDP_HTABLE_SIZE) so that we scan chains at most once. Instead of 250 ms per bind() call, we get after patch a time of 2.9 ms Based on a report from Vitaly Mayatskikh Reported-by: Vitaly Mayatskikh <v.mayatskih@gmail.com> Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> Tested-by: Vitaly Mayatskikh <v.mayatskih@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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