From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933939AbcIOHGJ (ORCPT ); Thu, 15 Sep 2016 03:06:09 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:34926 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759534AbcIOHEf (ORCPT ); Thu, 15 Sep 2016 03:04:35 -0400 Date: Thu, 15 Sep 2016 09:04:30 +0200 From: Ingo Molnar To: Denys Vlasenko Cc: Andy Lutomirski , "H. Peter Anvin" , Borislav Petkov , Brian Gerst , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2 v2] x86/e820: Use much less memory for e820/e820_saved, save up to 120k Message-ID: <20160915070430.GA25643@gmail.com> References: <20160909075827.14602-1-dvlasenk@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160909075827.14602-1-dvlasenk@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Denys Vlasenko wrote: > The maximum size of e820 map array for EFI systems is defined as > E820_X_MAX (E820MAX + 3 * MAX_NUMNODES). > > In x86_64 defconfig, this ends up with E820_X_MAX = 320, e820 and e820_saved > are 6404 bytes each. > > With larger configs, for example Fedora kernels, E820_X_MAX = 3200, e820 and e820_saved > are 64004 bytes each. Most of this space is wasted. Typical machines have some 20-30 > e820 areas at most. > > This patch turns e820 and e820_saved to pointers which initially point to __initdata > tables, of the same size as before. > > At the very end of setup_arch(), when we are done fiddling with these maps, > allocate smaller alloc_bootmem blocks, copy maps there, and change pointers. > > Run-tested. > +/* > + * Initial e820 and e820_saved are largish __initdata arrays. > + * Copy them to (usually much smaller) dynamically allocated area. > + * This is done after all tweaks we ever do to them. > + */ > +__init void e820_reallocate_tables(void) > +{ > + struct e820map *n; > + int size; > + > + size = offsetof(struct e820map, map) + sizeof(struct e820entry) * e820->nr_map; > + n = alloc_bootmem(size); > + memcpy(n, e820, size); > + e820 = n; > + > + size = offsetof(struct e820map, map) + sizeof(struct e820entry) * e820_saved->nr_map; > + n = alloc_bootmem(size); > + memcpy(n, e820_saved, size); > + e820_saved = n; > +} Ok, this makes me quite nervous, could you please split this into two patches so that any fails can be nicely bisected to? First patch only does the pointerization changes with a trivial placeholder structure (full size, static allocated), second patch does all the dangerous bits such as changing it to __initdata, allocating and copying over bits. Also, could we please also add some minimal debugging facility to make sure the memory table does not get extended after it's been reallocated? Thanks, Ingo