From patchwork Fri Jan 8 12:58:03 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Gerd Hoffmann X-Patchwork-Id: 564767 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 7F6E31402A8 for ; Fri, 8 Jan 2016 23:58:42 +1100 (AEDT) Received: from localhost ([::1]:35496 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aHWcq-0003wD-Ca for incoming@patchwork.ozlabs.org; Fri, 08 Jan 2016 07:58:40 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55920) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aHWcb-0003fX-3d for qemu-devel@nongnu.org; Fri, 08 Jan 2016 07:58:26 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aHWcW-0000Oc-2J for qemu-devel@nongnu.org; Fri, 08 Jan 2016 07:58:24 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39402) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aHWcV-0000O1-Qw for qemu-devel@nongnu.org; Fri, 08 Jan 2016 07:58:19 -0500 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) by mx1.redhat.com (Postfix) with ESMTPS id 2A98B37C36D; Fri, 8 Jan 2016 12:58:19 +0000 (UTC) Received: from nilsson.home.kraxel.org (ovpn-116-30.ams2.redhat.com [10.36.116.30]) by int-mx10.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u08CwGi9030906; Fri, 8 Jan 2016 07:58:18 -0500 Received: by nilsson.home.kraxel.org (Postfix, from userid 500) id 7F3A880823; Fri, 8 Jan 2016 13:58:13 +0100 (CET) From: Gerd Hoffmann To: qemu-devel@nongnu.org Date: Fri, 8 Jan 2016 13:58:03 +0100 Message-Id: <1452257883-19549-1-git-send-email-kraxel@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.23 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 209.132.183.28 Cc: Paolo Bonzini , "Michael S. Tsirkin" , Gerd Hoffmann , Eduardo Habkost , Richard Henderson Subject: [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-below-4g option X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org This patch extends the functionality of the max-ram-below-4g option to also allow increasing lowmem. Use case: Give as much memory as possible to legacy non-PAE guests. While being at it also rework the lowmem calculation logic and add a longish comment describing how it works and what the compatibility constrains are. Signed-off-by: Gerd Hoffmann Acked-by: Laszlo Ersek Reviewed-by: Marcel Apfelbaum Reviewed-by: Eduardo Habkost --- hw/i386/pc.c | 2 +- hw/i386/pc_piix.c | 61 +++++++++++++++++++++++++++++++++++-------------------- 2 files changed, 40 insertions(+), 23 deletions(-) diff --git a/hw/i386/pc.c b/hw/i386/pc.c index 459260b..1332269 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -1887,7 +1887,7 @@ static void pc_machine_initfn(Object *obj) pc_machine_get_hotplug_memory_region_size, NULL, NULL, NULL, &error_abort); - pcms->max_ram_below_4g = 1ULL << 32; /* 4G */ + pcms->max_ram_below_4g = 0xe0000000; /* 3.5G */ object_property_add(obj, PC_MACHINE_MAX_RAM_BELOW_4G, "size", pc_machine_get_max_ram_below_4g, pc_machine_set_max_ram_below_4g, diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c index 438cdae..3743736 100644 --- a/hw/i386/pc_piix.c +++ b/hw/i386/pc_piix.c @@ -87,29 +87,46 @@ static void pc_init1(MachineState *machine, PcGuestInfo *guest_info; ram_addr_t lowmem; - /* Check whether RAM fits below 4G (leaving 1/2 GByte for IO memory). - * If it doesn't, we need to split it in chunks below and above 4G. - * In any case, try to make sure that guest addresses aligned at - * 1G boundaries get mapped to host addresses aligned at 1G boundaries. - * For old machine types, use whatever split we used historically to avoid - * breaking migration. + /* + * Calculate ram split, for memory below and above 4G. It's a bit + * complicated for backward compatibility reasons ... + * + * - Traditional split is 3.5G (lowmem = 0xe0000000). This is the + * default value for max_ram_below_4g now. + * + * - Then, to gigabyte align the memory, we move the split to 3G + * (lowmem = 0xc0000000). But only in case we have to split in + * the first place, i.e. ram_size is larger than (traditional) + * lowmem. And for new machine types (gigabyte_align = true) + * only, for live migration compatibility reasons. + * + * - Next the max-ram-below-4g option was added, which allowed to + * reduce lowmem to a smaller value, to allow a larger PCI I/O + * window below 4G. qemu doesn't enforce gigabyte alignment here, + * but prints a warning. + * + * - Finally max-ram-below-4g got updated to also allow raising lowmem, + * so legacy non-PAE guests can get as much memory as possible in + * the 32bit address space below 4G. + * + * Examples: + * qemu -M pc-1.7 -m 4G (old default) -> 3584M low, 512M high + * qemu -M pc -m 4G (new default) -> 3072M low, 1024M high + * qemu -M pc,max-ram-below-4g=2G -m 4G -> 2048M low, 2048M high + * qemu -M pc,max-ram-below-4g=4G -m 3968M -> 3968M low (=4G-128M) */ - if (machine->ram_size >= 0xe0000000) { - lowmem = pcmc->gigabyte_align ? 0xc0000000 : 0xe0000000; - } else { - lowmem = 0xe0000000; - } - - /* Handle the machine opt max-ram-below-4g. It is basically doing - * min(qemu limit, user limit). - */ - if (lowmem > pcms->max_ram_below_4g) { - lowmem = pcms->max_ram_below_4g; - if (machine->ram_size - lowmem > lowmem && - lowmem & ((1ULL << 30) - 1)) { - error_report("Warning: Large machine and max_ram_below_4g(%"PRIu64 - ") not a multiple of 1G; possible bad performance.", - pcms->max_ram_below_4g); + lowmem = pcms->max_ram_below_4g; + if (machine->ram_size >= pcms->max_ram_below_4g) { + if (pcmc->gigabyte_align) { + if (lowmem > 0xc0000000) { + lowmem = 0xc0000000; + } + if (lowmem & ((1ULL << 30) - 1)) { + error_report("Warning: Large machine and max_ram_below_4g " + "(%" PRIu64 ") not a multiple of 1G; " + "possible bad performance.", + pcms->max_ram_below_4g); + } } }