From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 28 Nov 2007 00:48:21 +0100 From: Andi Kleen Subject: Re: [PATCH 1/1] mm: Prevent dereferencing non-allocated per_cpu variables Message-ID: <20071127234821.GC31491@one.firstfloor.org> References: <20071127215052.090968000@sgi.com> <20071127215054.660250000@sgi.com> <20071127221628.GG24223@one.firstfloor.org> <20071127151241.038c146d.akpm@linux-foundation.org> <20071127152122.1d5fbce3.akpm@linux-foundation.org> <20071127154213.11970e63.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071127154213.11970e63.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: Christoph Lameter , andi@firstfloor.org, travis@sgi.com, ak@suse.de, pageexec@freemail.hu, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Tue, Nov 27, 2007 at 03:42:13PM -0800, Andrew Morton wrote: > On Tue, 27 Nov 2007 15:22:56 -0800 (PST) > Christoph Lameter wrote: > > > On Tue, 27 Nov 2007, Andrew Morton wrote: > > > > > The prefetch however might still need some work - we can indeed do > > > prefetch() against a not-possible CPU's memory here. And I do recall that > > > 4-5 years ago we did have a CPU (one of mine, iirc) which would oops when > > > prefetching from a bad address. I forget what the conclusion was on that > > > matter. > > > > > > If we do want to fix the prefetch-from-outer-space then we should be using > > > cpu_isset(cpu, *cpumask) here rather than cpu_possible(). > > > > Generally the prefetch things have turned out to be not that useful. How > > about dropping the prefetch? I kept it because it was there. > > I don't recall anyone ever demonstrating that prefetch is useful in-kernel. It was demonstrated useful for some specific cases, like context switch early fetch on IA64. But I agree the prefetch on each list_for_each() is probably a bad idea and should be removed. Will also help code size. The best strategy is probably to figure out which oprofile counters to use and then do some profiling and only insert prefetches where the profiler actually finds significant cache misses. -Andi -- 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