From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751554AbeCLOw1 (ORCPT ); Mon, 12 Mar 2018 10:52:27 -0400 Received: from mail-lf0-f68.google.com ([209.85.215.68]:38699 "EHLO mail-lf0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751232AbeCLOwZ (ORCPT ); Mon, 12 Mar 2018 10:52:25 -0400 X-Google-Smtp-Source: AG47ELtxrCT1mX2ZjDWgKl2K6cTNLJ4qg3f6d/nxtQKaQwB3g5TcXyFpYaBlKqv+l+1/itAz1L6ROw== Date: Mon, 12 Mar 2018 17:52:22 +0300 From: Cyrill Gorcunov To: Ingo Molnar Cc: "Kirill A. Shutemov" , Peter Zijlstra , kirill.shutemov@linux.intel.com, luto@amacapital.net, keescook@chromium.org, willy@infradead.org, torvalds@linux-foundation.org, tglx@linutronix.de, bp@suse.de, andy.shevchenko@gmail.com, linux-kernel@vger.kernel.org, hpa@zytor.com, ebiederm@xmission.com, jgross@suse.com, linux-tip-commits@vger.kernel.org Subject: Re: [tip:x86/mm] x86/boot/compressed/64: Describe the logic behind the LA57 check Message-ID: <20180312145222.GC22761@uranus.lan> References: <20180226180451.86788-2-kirill.shutemov@linux.intel.com> <20180312124027.GG4064@hirez.programming.kicks-ass.net> <20180312124337.vw7bchm6brfzghfa@node.shutemov.name> <20180312131055.GH4064@hirez.programming.kicks-ass.net> <20180312140449.oyngtgqppnjuh3lf@node.shutemov.name> <20180312143212.77z2ptyqbsbqdll3@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180312143212.77z2ptyqbsbqdll3@gmail.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 12, 2018 at 03:32:12PM +0100, Ingo Molnar wrote: > > * Kirill A. Shutemov wrote: > > > > We can of course bike shed / benchmark this once my desktop refresh > > > sports this feature, but ISTR this being one of the very first things > > > Ingo mentioned when we started this whole 5L thing. > > > > I would rather not fix the problem that may not actually exist. :) > > That 5 level pagetables involve more overhead is a realy problem. > > By default we should only enable 5-level paging if memory mappings exist in > the memory map that require the extended physical memory space. Does it mean that if a machine supports 5lvl but has phisycal memory installed fitting the 4lvl space, and has memory hotplug supported, adding more memory won't have effect until next reboot?