[ovs-dev] [PATCH net-next v5 0/3] Lockless netlink_lookup() with new concurrent hash table

Thomas Graf tgraf at suug.ch
Sat Aug 2 09:47:43 UTC 2014

Netlink sockets are maintained in a hash table to allow efficient lookup
via the port ID for unicast messages. However, lookups currently require
a read lock to be taken. This series adds a new generic, resizable,
scalable, concurrent hash table based on the paper referenced in the first
patch. It then makes use of the new data type to implement lockless

Patch 3/3 to convert nft_hash is included for reference but should be
merged via the netfilter tree. Inclusion in this series is to provide
context for the suggested API.

Against net-next since the initial user of the new hash table is in net/

 - use GFP_KERNEL to alloc Netlink buckets as suggested by Nikolay
 - free nft hash element on removal as spotted by Nikolay Aleksandrov
   and Patrick McHardy
 - fixed wrong shift assignment placement as spotted by Nikolay Aleksandrov
 - reverted default size of nft_hash to 4 as requested by Patrick McHardy,
   default size for other hash tables remains at 64 if no hint is given
 - fixed copyright as requested by Patrick McHardy
 - fixed typo in nft_hash_destroy() when passing rhashtable handle
 - fixed traversal off-by-one as spotted by Tobias Klauser
 - removed unlikely() from BUG_ON() as spotted by Josh Triplett
 - new 3rd patch to convert nft_hash to rhashtable
 - make rhashtable_insert() return void
 - nl_sk_hash_lock must be a mutex
 - fixed wrong name of rht_shrink_below_30()
 - exported symbols rht_grow_above_75() and rht_shrink_below_30()
 - allow table freeing with RCU callback

Thomas Graf (3):
  lib: Resizable, Scalable, Concurrent Hash Table
  netlink: Convert netlink_lookup() to use RCU protected hash table
  nftables: Convert nft_hash to use generic rhashtable

 include/linux/rhashtable.h | 213 ++++++++++++
 lib/Kconfig.debug          |   8 +
 lib/Makefile               |   2 +-
 lib/rhashtable.c           | 797 +++++++++++++++++++++++++++++++++++++++++++++
 net/netfilter/nft_hash.c   | 291 ++++-------------
 net/netlink/af_netlink.c   | 285 ++++++----------
 net/netlink/af_netlink.h   |  18 +-
 net/netlink/diag.c         |  11 +-
 8 files changed, 1193 insertions(+), 432 deletions(-)
 create mode 100644 include/linux/rhashtable.h
 create mode 100644 lib/rhashtable.c


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