Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761872Ab3EBUDQ (ORCPT ); Thu, 2 May 2013 16:03:16 -0400 Received: from mail-ve0-f175.google.com ([209.85.128.175]:50958 "EHLO mail-ve0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755392Ab3EBUDP (ORCPT ); Thu, 2 May 2013 16:03:15 -0400 MIME-Version: 1.0 In-Reply-To: <20130501224604.21ebc42a@annuminas.surriel.com> References: <517B1153.8000401@valvesoftware.com> <517B2FB4.30605@redhat.com> <20130427024248.GA1229@cmpxchg.org> <517EEBD1.503@valvesoftware.com> <517F14D1.3070307@redhat.com> <20130502013426.GC9583@home.goodmis.org> <20130501224604.21ebc42a@annuminas.surriel.com> Date: Thu, 2 May 2013 13:03:14 -0700 X-Google-Sender-Auth: lUzQ-FInTiRUKPq512fBUzIKmjQ Message-ID: Subject: Re: [PATCH] mm,x86: limit 32 bit kernel to 12GB memory From: Linus Torvalds To: Rik van Riel Cc: Steven Rostedt , "Pierre-Loup A. Griffais" , Johannes Weiner , Linux Kernel Mailing List , sonnyrao@chromium.org, KAMEZAWA Hiroyuki , Andrew Morton Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2102 Lines: 45 On Wed, May 1, 2013 at 7:46 PM, Rik van Riel wrote: > > Here's a somewhat friendlier one. Printing out the total amount of > memory in the system may give them some extra motivation to upgrade > to a 64 bit kernel :) This needs more work: - suggesting a 64-bit kernel on a truly 32-bit CPU is insane, so it had better actually check the CPUID for 64-bit support ("lm" for "long mode"). - we don't remove features, so there should be a kernel command line option to say "I'm insane, I know this is going to have problems, I want you to try to use more memory anyway" and disable the new 12GB limit - I don't think it's necessarily "system stability". The problem with large amounts of highmem ends up being that we end up using up almost all of the lowmem just to *track* the huge amount of highmem, and then we have so little lowmem that we suck at performance and have various random problems. So it's not just "system stability", it's more fluid than that. The "it's more fluid than that" is also why I'd want to have a way to override it. Using up all lowmem to track highmem is actually ok under some very specific loads. If you have a setup where you have tons of highmem, but all it is ever used for is anonymous user pages, you don't need a lot of lowmem. Some of the craziest PAE users were that class of use, and for all we know there are still crazy people with real 32-bit CPU's that want to do it. We don't really want to support it, we don't really care, but I don't think we want to then say "you cannot do that" either. We want to say "you're a f*cking crazy moron, and we don't think what you do is a good idea, but if if you absolutely want to shoot yourself in the foot, here's how to do it. Don't expect things to work well in general, but you might have a load where it's acceptable". Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/