From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 3 Jan 2008 04:32:46 +0100 From: Nick Piggin Subject: Re: [patch] mm: fix PageUptodate memory ordering bug Message-ID: <20080103033245.GA26487@wotan.suse.de> References: <20071218012632.GA23110@wotan.suse.de> <20071230163315.GA1384@elte.hu> <20080101232634.GA29301@wotan.suse.de> <200801022201.28025.ak@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200801022201.28025.ak@suse.de> Sender: owner-linux-mm@kvack.org Return-Path: To: Andi Kleen Cc: Ingo Molnar , Andrew Morton , Hugh Dickins , Linux Memory Management List , Benjamin Herrenschmidt , Linus Torvalds , Alan Cox List-ID: On Wed, Jan 02, 2008 at 10:01:27PM +0100, Andi Kleen wrote: > On Wednesday 02 January 2008 00:26:34 Nick Piggin wrote: > > On Sun, Dec 30, 2007 at 05:33:15PM +0100, Ingo Molnar wrote: > > > > > > * Nick Piggin wrote: > > > > > > > > Sounds worthwhile, if we can't do it via altinstructions. > > > > > > > > Altinstructions means we still have code bloat, and sometimes extra > > > > branches etc (an extra 900 bytes of icache in mm/ alone, even before > > > > my fix). I'll let Linus or one of the x86 guys weigh in, though. It's > > > > a really sad cost for distro kernels to carry. > > > > > > hm, we should at minimum display a warning if the workaround is not > > > enabled and such a kernel is booted on a true PPro that is affected by > > > this. > > > > The patch does have the warning: > > printk(KERN_INFO "Pentium Pro with Errata#66, #92 detected. Limiting maxcpus to 1. > > Enable CONFIG_X86_BROKEN_PPRO_SMP to run with multiple CPUs\n"); > > Haven't seen the full patch, but the printk suggest you're changing the max_cpus > variable. That is not 100% safe because user space could hot plug CPUs later > using sysfs. The only safe way would be to limit cpu_possible_map Hmm, but I did want to allow it to be overridden via maxcpus= command line (or hotplug I guess, I hadn't thought of the hotplug case but it allows runtime override). -- 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