From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 2 Mar 2007 14:59:06 -0800 From: Andrew Morton Subject: Re: The performance and behaviour of the anti-fragmentation related patches Message-Id: <20070302145906.653d3b82.akpm@linux-foundation.org> In-Reply-To: <45E8A677.7000205@redhat.com> References: <20070301101249.GA29351@skynet.ie> <20070301160915.6da876c5.akpm@linux-foundation.org> <45E842F6.5010105@redhat.com> <20070302085838.bcf9099e.akpm@linux-foundation.org> <20070302093501.34c6ef2a.akpm@linux-foundation.org> <45E8624E.2080001@redhat.com> <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> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Rik van Riel Cc: 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, 02 Mar 2007 17:34:31 -0500 Rik van Riel wrote: > >>>> The main reason they end up pounding the LRU locks is the > >>>> swappiness heuristic. They scan too much before deciding > >>>> that it would be a good idea to actually swap something > >>>> out, and with 32 CPUs doing such scanning simultaneously... > >>> What kernel version? > >> Customers are on the 2.6.9 based RHEL4 kernel, but I believe > >> we have reproduced the problem on 2.6.18 too during stress > >> tests. > > > > The prev_priority fixes were post-2.6.18 > > We tested them. They only alleviate the problem slightly in > good situations, but things still fall apart badly with less > friendly workloads. What is it with vendors finding MM problems and either not fixing them or kludging around them and not telling the upstream maintainers about *any* of it? > >> I have no reason to believe we should stick our heads in the > >> sand and pretend it no longer exists on 2.6.21. > > > > I have no reason to believe anything. All I see is handwaviness, > > speculation and grand plans to rewrite vast amounts of stuff without even a > > testcase to demonstrate that said rewrite improved anything. > > Your attitude is exactly why the VM keeps falling apart over > and over again. > > Fixing "a testcase" in the VM tends to introduce problems for > other test cases, ad infinitum. In that case it was a bad fix. The aim is to fix known problems without introducing regressions in other areas. A perfectly legitimate approach. You seem to be saying that we'd be worse off if we actually had a testcase. > There's a reason we end up > fixing the same bugs over and over again. No we don't. > I have been looking through a few hundred VM related bugzillas > and have found the same bugs persist over many different > versions of Linux, sometimes temporarily fixed, but they seem > to always come back eventually... > > > None of this is going anywhere, is is it? > > I will test my changes before I send them to you, but I cannot > promise you that you'll have the computers or software needed > to reproduce the problems. I doubt I'll have full time access > to such systems myself, either. > > 32GB is pretty much the minimum size to reproduce some of these > problems. Some workloads may need larger systems to easily trigger 32GB isn't particularly large. 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. -- 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