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Date: Sun, 23 Nov 2008 14:33:00 -0800 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Eric Dumazet <dada1@...mosbay.com> Cc: David Miller <davem@...emloft.net>, Corey Minyard <minyard@....org>, Stephen Hemminger <shemminger@...tta.com>, benny+usenet@...rsen.dk, Linux Netdev List <netdev@...r.kernel.org>, Christoph Lameter <cl@...ux-foundation.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Evgeniy Polyakov <zbr@...emap.net>, Christian Bell <christian@...i.com> Subject: Re: [PATCH] net: Convert TCP/DCCP listening hash tables to use RCU On Sun, Nov 23, 2008 at 09:18:17PM +0100, Eric Dumazet wrote: > Paul E. McKenney a écrit : >> On Sun, Nov 23, 2008 at 07:42:14PM +0100, Eric Dumazet wrote: >>> Paul E. McKenney a écrit : >>>> On Sun, Nov 23, 2008 at 10:33:28AM +0100, Eric Dumazet wrote: >>>>> Hi David >>>>> >>>>> Please find patch to convert TCP/DCCP listening hash tables >>>>> to RCU. >>>>> >>>>> A followup patch will cleanup all sk_node fields and macros >>>>> that are not used anymore. >>>>> >>>>> Thanks >>>>> >>>>> [PATCH] net: Convert TCP/DCCP listening hash tables to use RCU >>>>> >>>>> This is the last step to be able to perform full RCU lookups >>>>> in __inet_lookup() : After established/timewait tables, we >>>>> add RCU lookups to listening hash table. >>>>> >>>>> The only trick here is that a socket of a given type (TCP ipv4, >>>>> TCP ipv6, ...) can now flight between two different tables >>>>> (established and listening) during a RCU grace period, so we >>>>> must use different 'nulls' end-of-chain values for two tables. >>>>> >>>>> We define a large value : >>>>> >>>>> #define LISTENING_NULLS_BASE (1U << 29) >>>> I do like this use of the full set up upper bits! However, wouldn't it >>>> be a good idea to use a larger base value for 64-bit systems, perhaps >>>> using CONFIG_64BIT to choose? 500M entries might not seem like that >>>> many in a few years time... >>> Well, this value is correct up to 2^29 slots, and a hash table of 2^32 >>> bytes >>> (8 bytes per pointer) >>> >>> A TCP socket uses about 1472 bytes on 64bit arches, so 2^29 sessions >>> would need 800 GB of ram, not counting dentries, inodes, ... >>> >>> I really doubt a machine, even with 4096 cpus should/can handle so many >>> tcp sessions :) >> 200MB per CPU, right? >> But yes, now that you mention it, 800GB of memory dedicated to TCP >> connections sounds almost as ridiculous as did 640K of memory in the >> late 1970s. ;-) > > ;) > >> Nevertheless, I don't have an overwhelming objection to the current >> code. Easy enough to change should it become a problem, right? > > Sure. By that time, cpus might be 128 bits or 256 bits anyway :) Or even 640K bits. ;-) Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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