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We added an automatic route cache rebuilding in commit 1080d709fb9d8cd43 but had to correct few bugs. One of the assumption of original patch, was that entries where kept sorted in a given way. This assumption is known to be wrong (commit 1ddbcb005c395518 gave an explanation of this and corrected a leak) and expensive to respect. Paweł Staszewski reported to me one of his machine got its routing cache disabled after few messages like : [ 2677.850065] Route hash chain too long! [ 2677.850080] Adjust your secret_interval! [82839.662993] Route hash chain too long! [82839.662996] Adjust your secret_interval! [155843.731650] Route hash chain too long! [155843.731664] Adjust your secret_interval! [155843.811881] Route hash chain too long! [155843.811891] Adjust your secret_interval! [155843.858209] vlan0811: 5 rebuilds is over limit, route caching disabled [155843.858212] Route hash chain too long! [155843.858213] Adjust your secret_interval! This is because rt_intern_hash() might be fooled when computing a chain length, because multiple entries with same keys can differ because of TOS (or mark/oif) bits. In the rare case the fast algorithm see a too long chain, and before taking expensive path, we call a helper function in order to not count duplicates of same routes, that only differ with tos/mark/oif bits. This helper works with data already in cpu cache and is not be very expensive, despite its O(N^2) implementation. Paweł Staszewski sucessfully tested this patch on his loaded router. Reported-and-tested-by: Paweł Staszewski <pstaszewski@itcare.pl> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Acked-by: Neil Horman <nhorman@tuxdriver.com> Signed-off-by: David S. Miller <davem@davemloft.net>