From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751591AbdJWMWE (ORCPT ); Mon, 23 Oct 2017 08:22:04 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:47881 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751280AbdJWMWC (ORCPT ); Mon, 23 Oct 2017 08:22:02 -0400 X-Google-Smtp-Source: ABhQp+RVXCxL5DiizYtXLJLCPsIVZG6r/lcc2kF/R1RiONAtjtlihC3knhsYZvxZb9Z0sqn3xofqig== Date: Mon, 23 Oct 2017 15:21:59 +0300 From: "Kirill A. Shutemov" To: Ingo Molnar 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: <20171023122159.wyztmsbgt5k2d4tb@node.shutemov.name> 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> <20171023115658.geccs22o2t733np3@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171023115658.geccs22o2t733np3@gmail.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 23, 2017 at 01:56:58PM +0200, Ingo Molnar wrote: > > * 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 wast majority of > > cases. > > Almost nothing uses it - and even in those few cases it caused problems. It's used in many places indirectly. See MAXMEM. > Making a variable that 'looks' like a constant macro dynamic in a rare Kconfig > scenario is asking for trouble. We expect boot-time page mode switching to be enabled in kernel of next generation enterprise distros. It shoudn't be that rare. -- Kirill A. Shutemov From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f200.google.com (mail-wr0-f200.google.com [209.85.128.200]) by kanga.kvack.org (Postfix) with ESMTP id 5980E6B0033 for ; Mon, 23 Oct 2017 08:22:03 -0400 (EDT) Received: by mail-wr0-f200.google.com with SMTP id z55so9990226wrz.2 for ; Mon, 23 Oct 2017 05:22:03 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id j9sor3617148edf.30.2017.10.23.05.22.01 for (Google Transport Security); Mon, 23 Oct 2017 05:22:02 -0700 (PDT) Date: Mon, 23 Oct 2017 15:21:59 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH 0/6] Boot-time switching between 4- and 5-level paging for 4.15, Part 1 Message-ID: <20171023122159.wyztmsbgt5k2d4tb@node.shutemov.name> 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> <20171023115658.geccs22o2t733np3@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171023115658.geccs22o2t733np3@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Ingo Molnar 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 On Mon, Oct 23, 2017 at 01:56:58PM +0200, Ingo Molnar wrote: > > * 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 wast majority of > > cases. > > Almost nothing uses it - and even in those few cases it caused problems. It's used in many places indirectly. See MAXMEM. > Making a variable that 'looks' like a constant macro dynamic in a rare Kconfig > scenario is asking for trouble. We expect boot-time page mode switching to be enabled in kernel of next generation enterprise distros. It shoudn't be that rare. -- Kirill A. Shutemov -- 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