From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pablo Neira Ayuso Subject: Re: [PATCH v3] netfilter: nft_hash: bug fixes and resizing Date: Fri, 7 Mar 2014 11:49:02 +0100 Message-ID: <20140307104902.GA12188@localhost> References: <1393946511-28174-1-git-send-email-kaber@trash.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netfilter-devel@vger.kernel.org, josh@joshtriplett.org, paulmck@linux.vnet.ibm.com To: Patrick McHardy Return-path: Received: from mail.us.es ([193.147.175.20]:47373 "EHLO mail.us.es" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752099AbaCGKtH (ORCPT ); Fri, 7 Mar 2014 05:49:07 -0500 Content-Disposition: inline In-Reply-To: <1393946511-28174-1-git-send-email-kaber@trash.net> Sender: netfilter-devel-owner@vger.kernel.org List-ID: On Tue, Mar 04, 2014 at 04:21:51PM +0100, Patrick McHardy wrote: > The hash set type is very broken and was never meant to be merged in this > state. Missing RCU synchronization on element removal, leaking chain > refcounts when used as a verdict map, races during lookups, a fixed table > size are probably just some of the problems. Luckily it is currently > never chosen by the kernel when the rbtree type is also available. > > Rewrite it to be usable. > > The new implementation supports automatic hash table resizing using RCU, > based on Paul McKenney's and Josh Triplett's algorithm "Optimized Resizing > For RCU-Protected Hash Tables" described in [1]. > > Resizing doesn't require a second list head in the elements, it works by > chosing a hash function that remaps elements to a predictable set of buckets, > only resizing by integral factors and > > - during expansion: linking new buckets to the old bucket that contains > elements for any of the new buckets, thereby creating imprecise chains, > then incrementally seperating the elements until the new buckets only > contain elements that hash directly to them. > > - during shrinking: linking the hash chains of all old buckets that hash > to the same new bucket to form a single chain. > > Expansion requires at most the number of elements in the longest hash chain > grace periods, shrinking requires a single grace period. > > Due to the requirement of having hash chains/elements linked to multiple > buckets during resizing, homemade single linked lists are used instead of > the existing list helpers, that don't support this in a clean fashion. > As a side effect, the amount of memory required per element is reduced by > one pointer. > > Expansion is triggered when the load factors exceeds 75%, shrinking when > the load factor goes below 30%. Both operations are allowed to fail and > will be retried on the next insertion or removal if their respective > conditions still hold. Applied, thanks Patrick.