From patchwork Thu Jun 2 08:48:25 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Gerd Hoffmann X-Patchwork-Id: 9149563 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 7B0FE6074E for ; Thu, 2 Jun 2016 08:51:03 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6B44E25E13 for ; Thu, 2 Jun 2016 08:51:03 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 5F6F32679B; Thu, 2 Jun 2016 08:51:03 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.9 required=2.0 tests=BAYES_00,FSL_HELO_HOME, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id CFB0525E13 for ; Thu, 2 Jun 2016 08:51:02 +0000 (UTC) Received: from localhost ([::1]:46080 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b8OLF-0002cj-K7 for patchwork-qemu-devel@patchwork.kernel.org; Thu, 02 Jun 2016 04:51:01 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45738) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b8OIw-000142-UW for qemu-devel@nongnu.org; Thu, 02 Jun 2016 04:48:40 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b8OIq-0008Dz-VR for qemu-devel@nongnu.org; Thu, 02 Jun 2016 04:48:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51613) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b8OIq-0008Dv-NP for qemu-devel@nongnu.org; Thu, 02 Jun 2016 04:48:32 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (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 46D6C7F6B0; Thu, 2 Jun 2016 08:48:32 +0000 (UTC) Received: from nilsson.home.kraxel.org (ovpn-116-36.ams2.redhat.com [10.36.116.36]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u528mVah006285; Thu, 2 Jun 2016 04:48:31 -0400 Received: by nilsson.home.kraxel.org (Postfix, from userid 500) id 8A2C581C25; Thu, 2 Jun 2016 10:48:30 +0200 (CEST) From: Gerd Hoffmann To: qemu-devel@nongnu.org Date: Thu, 2 Jun 2016 10:48:25 +0200 Message-Id: <1464857305-26675-1-git-send-email-kraxel@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Thu, 02 Jun 2016 08:48:32 +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] [PATCH v2] 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+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP 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. Note: This is a incompatible change. When setting max-ram-below-4g to a value larger than 3.5G (or 3G with gigabyte alignment) it has no effect on older qemu versions: qemu silently ignores it. With the patch applied it actually has an effect and changes the ram layout. Highly unlikely to hit in practive though as there is no reason start old qemu versions that way. 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); + } } }