From: David S. Miller Date: Tue, 24 Mar 2015 02:07:56 +0000 (-0400) Subject: Merge branch 'rhashtable-next' X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=cc330b55903aad9bce554427a0181d1ee3873b7c;p=openwrt%2Fstaging%2Fblogic.git Merge branch 'rhashtable-next' Herbert Xu says: ==================== rhashtable: Multiple rehashing This series introduces multiple rehashing. Recall that the original implementation in br_multicast used two list pointers per hash node and therefore is limited to at most one rehash at a time since you need one list pointer for the old table and one for the new table. Thanks to Josh Triplett's suggestion of using a single list pointer we're no longer limited by that. So it is perfectly OK to have an arbitrary number of tables in existence at any one time. The reader and removal simply has to walk from the oldest table to the newest table in order not to miss anything. Insertion without lookup are just as easy as we simply go to the last table that we can find and add the entry there. However, insertion with uniqueness lookup is more complicated because we need to ensure that two simultaneous insertions of the same key do not both succeed. To achieve this, all insertions including those without lookups are required to obtain the bucket lock from the oldest hash table that is still alive. This is determined by having the rehasher (there is only one rehashing thread in the system) keep a pointer of where it is up to. If a bucket has already been rehashed then it is dead, i.e., there cannot be any more insertions to it, otherwise it is considered alive. This guarantees that the same key cannot be inserted in two different tables in parallel. Patch 1 is actually a bug fix for the walker. Patch 2-5 eliminates unnecessary out-of-line copies of jhash. Patch 6 makes rhashtable_shrink shrink to fit. Patch 7 introduces multiple rehashing. This means that if we decide to grow then we will grow regardless of whether the previous one has finished. However, this is still asynchronous meaning that if insertions come fast enough we may still end up with a table that is overutilised. Patch 8 adds support for GFP_ATOMIC allocations of struct bucket_table. Finally patch 9 enables immediate rehashing. This is done either when the table reaches 100% utilisation, or when the chain length exceeds 16 (the latter can be disabled on request, e.g., for nft_hash. With these patches the system should no longer have any trouble dealing with fast insertions on a small table. In the worst case you end up with a list of tables that's log N in length while the rehasher catches up. v3 restores rhashtable_shrink and fixes a number of bugs in the multiple rehashing patches (7 and 9). ==================== Signed-off-by: David S. Miller --- cc330b55903aad9bce554427a0181d1ee3873b7c