From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 2 Mar 2007 17:58:56 -0800 From: Andrew Morton Subject: Re: The performance and behaviour of the anti-fragmentation related patches Message-Id: <20070302175856.bb9de72d.akpm@linux-foundation.org> In-Reply-To: <20070303014004.GC23573@holomorphy.com> References: <20070302100619.cec06d6a.akpm@linux-foundation.org> <45E86BA0.50508@redhat.com> <20070302211207.GJ10643@holomorphy.com> <45E894D7.2040309@redhat.com> <20070302135243.ada51084.akpm@linux-foundation.org> <45E89F1E.8020803@redhat.com> <20070302142256.0127f5ac.akpm@linux-foundation.org> <45E8A677.7000205@redhat.com> <20070302145906.653d3b82.akpm@linux-foundation.org> <20070303014004.GC23573@holomorphy.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: William Lee Irwin III Cc: Rik van Riel , Bill Irwin , Christoph Lameter , Mel Gorman , npiggin@suse.de, mingo@elte.hu, jschopp@austin.ibm.com, arjan@infradead.org, torvalds@linux-foundation.org, mbligh@mbligh.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Fri, 2 Mar 2007 17:40:04 -0800 William Lee Irwin III wrote: > On Fri, Mar 02, 2007 at 02:59:06PM -0800, Andrew Morton wrote: > > Somehow I don't believe that a person or organisation which is incapable of > > preparing even a simple testcase will be capable of fixing problems such as > > this without breaking things. > > My gut feeling is to agree, but I get nagging doubts when I try to > think of how to boil things like [major benchmarks whose names are > trademarked/copyrighted/etc. censored] down to simple testcases. Some > other things are obvious but require vast resources, like zillions of > disks fooling throttling/etc. heuristics of ancient downrev kernels. noooooooooo. You're approaching it from the wrong direction. Step 1 is to understand what is happening on the affected production system. Completely. Once that is fully understood then it is a relatively simple matter to concoct a test case which triggers the same failure mode. It is very hard to go the other way: to poke around with various stress tests which you think are doing something similar to what you think the application does in the hope that similar symptoms will trigger so you can then work out what the kernel is doing. yuk. -- 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