From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH 2/2] tuntap: limit the number of flow caches Date: Thu, 24 Jan 2013 11:22:52 +0800 Message-ID: <5100A90C.2030406@redhat.com> References: <1358949553-30309-1-git-send-email-jasowang@redhat.com> <1358949553-30309-2-git-send-email-jasowang@redhat.com> <20130123.135024.1407137924304146015.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: mst@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stephen@networkplumber.org To: David Miller Return-path: In-Reply-To: <20130123.135024.1407137924304146015.davem@davemloft.net> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 01/24/2013 02:50 AM, David Miller wrote: > From: Jason Wang > Date: Wed, 23 Jan 2013 21:59:13 +0800 > >> We create new flow caches when a new flow is identified by tuntap, This may lead >> some issues: >> >> - userspace may produce a huge amount of short live flows to exhaust host memory >> - the unlimited number of flow caches may produce a long list which increase the >> time in the linear searching >> >> Solve this by introducing a limit of total number of flow caches. >> >> Cc: Stephen Hemminger >> Signed-off-by: Jason Wang >> --- > Applied, but really flow caches are an extremely broken concept especially > when external entities control the population of such caches. > > We removed the routing cache of the ipv4 networking code exactly because > this kind of crap does not work at all. > > Next you're going to have to add a delicately managed garbage > collection scheme for this tuntap flow cache, and that will be tuned > endlessly, when the real issue is that fundamentally this does not > work. > > Instead, make the full lookup scale properly and use appropriate data > structures. It won't be as fast as a simple hash table demux, but > it'll actually be immune to growth issues and DoS attacks and give > consistent and repeatable lookup performance regardless of traffic > patterns. Ok, I will rework it in 3.9. Thanks > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html