From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932239AbdJWL5J (ORCPT ); Mon, 23 Oct 2017 07:57:09 -0400 Received: from mail-wm0-f54.google.com ([74.125.82.54]:52323 "EHLO mail-wm0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932096AbdJWL5H (ORCPT ); Mon, 23 Oct 2017 07:57:07 -0400 X-Google-Smtp-Source: ABhQp+Tod+PeYf/1v07G2b8UQF3eGzd1W9OdmN71GYv4FWnR3jGSFyYLn0au7ffDaDHWFrq2piwXZg== Date: Mon, 23 Oct 2017 13:56:58 +0200 From: Ingo Molnar To: "Kirill A. Shutemov" Cc: "Kirill A. Shutemov" , Ingo Molnar , Linus Torvalds , x86@kernel.org, Thomas Gleixner , "H. Peter Anvin" , Andrew Morton , Andy Lutomirski , Cyrill Gorcunov , Borislav Petkov , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/6] Boot-time switching between 4- and 5-level paging for 4.15, Part 1 Message-ID: <20171023115658.geccs22o2t733np3@gmail.com> References: <20170929140821.37654-1-kirill.shutemov@linux.intel.com> <20171003082754.no6ym45oirah53zp@node.shutemov.name> <20171017154241.f4zaxakfl7fcrdz5@node.shutemov.name> <20171020081853.lmnvaiydxhy5c63t@gmail.com> <20171020094152.skx5sh5ramq2a3vu@black.fi.intel.com> <20171020152346.f6tjybt7i5kzbhld@gmail.com> <20171020162349.3kwhdgv7qo45w4lh@node.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171020162349.3kwhdgv7qo45w4lh@node.shutemov.name> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Kirill A. Shutemov wrote: > > Or, could we keep MAX_PHYSMEM_BITS constant, and introduce a _different_ constant > > that is dynamic, and which could be used in the cases where the 5-level paging > > config causes too much memory footprint in the common 4-level paging case? > > This is more labor intensive case with unclear benefit. > > Dynamic MAX_PHYSMEM_BITS doesn't cause any issue in waste majority of > cases. Almost nothing uses it - and even in those few cases it caused problems. Making a variable that 'looks' like a constant macro dynamic in a rare Kconfig scenario is asking for trouble. Thanks, Ingo From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id EA1606B0033 for ; Mon, 23 Oct 2017 07:57:07 -0400 (EDT) Received: by mail-wm0-f72.google.com with SMTP id r202so6623096wmd.17 for ; Mon, 23 Oct 2017 04:57:07 -0700 (PDT) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id b74sor1204385wme.62.2017.10.23.04.57.06 for (Google Transport Security); Mon, 23 Oct 2017 04:57:06 -0700 (PDT) Date: Mon, 23 Oct 2017 13:56:58 +0200 From: Ingo Molnar Subject: Re: [PATCH 0/6] Boot-time switching between 4- and 5-level paging for 4.15, Part 1 Message-ID: <20171023115658.geccs22o2t733np3@gmail.com> References: <20170929140821.37654-1-kirill.shutemov@linux.intel.com> <20171003082754.no6ym45oirah53zp@node.shutemov.name> <20171017154241.f4zaxakfl7fcrdz5@node.shutemov.name> <20171020081853.lmnvaiydxhy5c63t@gmail.com> <20171020094152.skx5sh5ramq2a3vu@black.fi.intel.com> <20171020152346.f6tjybt7i5kzbhld@gmail.com> <20171020162349.3kwhdgv7qo45w4lh@node.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171020162349.3kwhdgv7qo45w4lh@node.shutemov.name> Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: "Kirill A. Shutemov" , Ingo Molnar , Linus Torvalds , x86@kernel.org, Thomas Gleixner , "H. Peter Anvin" , Andrew Morton , Andy Lutomirski , Cyrill Gorcunov , Borislav Petkov , linux-mm@kvack.org, linux-kernel@vger.kernel.org * Kirill A. Shutemov wrote: > > Or, could we keep MAX_PHYSMEM_BITS constant, and introduce a _different_ constant > > that is dynamic, and which could be used in the cases where the 5-level paging > > config causes too much memory footprint in the common 4-level paging case? > > This is more labor intensive case with unclear benefit. > > Dynamic MAX_PHYSMEM_BITS doesn't cause any issue in waste majority of > cases. Almost nothing uses it - and even in those few cases it caused problems. Making a variable that 'looks' like a constant macro dynamic in a rare Kconfig scenario is asking for trouble. Thanks, Ingo -- 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