From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 27 Nov 2007 15:42:13 -0800 From: Andrew Morton Subject: Re: [PATCH 1/1] mm: Prevent dereferencing non-allocated per_cpu variables Message-Id: <20071127154213.11970e63.akpm@linux-foundation.org> In-Reply-To: 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> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: 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, 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. I think I've heard of situations where benefits have been seen in userspace - if a loop does a lot of calculation on each datum which it fetches then there's a good opportunity to pipeline the fetch with the on-core crunching. But kernel doesn't do that sort of thing.. -- 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