From patchwork Wed Jun 1 12:28:11 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Gerd Hoffmann X-Patchwork-Id: 628652 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 3rKV6833NKz9t7w for ; Wed, 1 Jun 2016 22:29:20 +1000 (AEST) Received: from localhost ([::1]:41976 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b85Gw-0005LX-6b for incoming@patchwork.ozlabs.org; Wed, 01 Jun 2016 08:29:18 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47457) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b85G1-0004gd-Vl for qemu-devel@nongnu.org; Wed, 01 Jun 2016 08:28:23 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b85G0-00010k-Me for qemu-devel@nongnu.org; Wed, 01 Jun 2016 08:28:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42246) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b85G0-00010f-E3 for qemu-devel@nongnu.org; Wed, 01 Jun 2016 08:28:20 -0400 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 0E7A280F92; Wed, 1 Jun 2016 12:28:20 +0000 (UTC) Received: from nilsson.home.kraxel.org (ovpn-116-24.ams2.redhat.com [10.36.116.24]) by int-mx14.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u51CSJBd012216; Wed, 1 Jun 2016 08:28:19 -0400 Received: by nilsson.home.kraxel.org (Postfix, from userid 500) id 9781081BEC; Wed, 1 Jun 2016 14:28:18 +0200 (CEST) From: Gerd Hoffmann To: qemu-devel@nongnu.org Date: Wed, 1 Jun 2016 14:28:11 +0200 Message-Id: <1464784092-28298-1-git-send-email-kraxel@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.27 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Wed, 01 Jun 2016 12:28:20 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [RESEND PATCH] pc: allow raising low memory via max-ram-below-4g option X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , Richard Henderson , Gerd Hoffmann , Eduardo Habkost , "Michael S. Tsirkin" Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" 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 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 e29ccc8..bfaf5a3 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -1893,7 +1893,7 @@ 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 24e7042..7b4790f 100644 --- a/hw/i386/pc_piix.c +++ b/hw/i386/pc_piix.c @@ -87,29 +87,46 @@ static void pc_init1(MachineState *machine, MemoryRegion *rom_memory; 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); + } } }