From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 3 Aug 2007 02:20:10 +0200 From: Nick Piggin Subject: Re: [rfc] balance-on-fork NUMA placement Message-ID: <20070803002010.GB14775@wotan.suse.de> References: <20070731054142.GB11306@wotan.suse.de> <200707311114.09284.ak@suse.de> <20070801002313.GC31006@wotan.suse.de> <46B0C8A3.8090506@mbligh.org> <1185993169.5059.79.camel@localhost> <46B10E9B.2030907@mbligh.org> <20070802013631.GA15595@wotan.suse.de> <46B22383.5020109@mbligh.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <46B22383.5020109@mbligh.org> Sender: owner-linux-mm@kvack.org Return-Path: To: Martin Bligh Cc: Lee Schermerhorn , Andi Kleen , Ingo Molnar , Linux Kernel Mailing List , Linux Memory Management List , Eric Whitney List-ID: On Thu, Aug 02, 2007 at 11:33:39AM -0700, Martin Bligh wrote: > Nick Piggin wrote: > >On Wed, Aug 01, 2007 at 03:52:11PM -0700, Martin Bligh wrote: > >>>And so forth. Initial forks will balance. If the children refuse to > >>>die, forks will continue to balance. If the parent starts seeing short > >>>lived children, fork()s will eventually start to stay local. > >>Fork without exec is much more rare than without. Optimising for > >>the uncommon case is the Wrong Thing to Do (tm). What we decided > > > >It's only the wrong thing to do if it hurts the common case too > >much. Considering we _already_ balance on exec, then adding another > >balance on fork is not going to introduce some order of magnitude > >problem -- at worst it would be 2x but it really isn't too slow > >anyway (at least nobody complained when we added it). > > > >One place where we found it helps is clone for threads. > > > >If we didn't do such a bad job at keeping tasks together with their > >local memory, then we might indeed reduce some of the balance-on-crap > >and increase the aggressiveness of periodic balancing. > > > >Considering we _already_ balance on fork/clone, I don't know what > >your argument is against this patch is? Doing the balance earlier > >and allocating more stuff on the local node is surely not a bad > >idea. > > I don't know who turned that on ;-( I suspect nobody bothered > actually measuring it at the time though, or used some crap > benchmark like stream to do so. It should get reverted. So you have numbers to show it hurts? I tested some things where it is not supposed to help, and it didn't make any difference. Nobody else noticed either. If the cost of doing the double balance is _really_ that painful, then we ccould skip balance-on-exec for domains with balance-on-fork set. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org