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banners=-,-,- X-VirusChecked: Checked Received: (qmail 26656 invoked from network); 24 Jun 2016 05:46:27 -0000 Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by server-4.tower-206.messagelabs.com with DHE-RSA-AES256-GCM-SHA384 encrypted SMTP; 24 Jun 2016 05:46:27 -0000 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 6ECB3C05FBB3; Fri, 24 Jun 2016 05:46:25 +0000 (UTC) Received: from nilsson.home.kraxel.org (ovpn-116-29.ams2.redhat.com [10.36.116.29]) by int-mx14.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u5O5kOmK026608; Fri, 24 Jun 2016 01:46:24 -0400 Received: by nilsson.home.kraxel.org (Postfix, from userid 500) id 89BD480519; Fri, 24 Jun 2016 07:46:23 +0200 (CEST) Message-ID: <1466747183.16435.1.camel@redhat.com> From: Gerd Hoffmann To: Anthony PERARD Date: Fri, 24 Jun 2016 07:46:23 +0200 In-Reply-To: <20160623161847.GT5666@perard.uk.xensource.com> References: <20160622150937.GS5666@perard.uk.xensource.com> <1466693874.26189.50.camel@redhat.com> <20160623161847.GT5666@perard.uk.xensource.com> Mime-Version: 1.0 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 [10.5.110.32]); Fri, 24 Jun 2016 05:46:25 +0000 (UTC) Cc: Paolo Bonzini , Stefano Stabellini , qemu-devel@nongnu.org, xen-devel@lists.xen.org Subject: Re: [Xen-devel] Change of max-ram-below-4g initial value breaks Xen X-BeenThere: xen-devel@lists.xen.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xen.org Sender: "Xen-devel" X-Virus-Scanned: ClamAV using ClamSMTP On Do, 2016-06-23 at 17:18 +0100, Anthony PERARD wrote: > On Thu, Jun 23, 2016 at 04:57:54PM +0200, Gerd Hoffmann wrote: > > Hi, > > > > > How could xen_ram_init() find out if the value of max-ram-below-4g is > > > the default or if a user have set it? Is there another way we could fix > > > this? > > > > Attached patch should fix it. Patch survived a quick smoke test on kvm > > so far, need to do some more testing tomorrow. Can you give it a spin > > on xen? > > Thanks. Unfortunately, it does not work :(. > > In this patch, max_ram_below_4g is set before the call to xen_ram_init() > and xen_ram_init read it back (via object_property_get_int()). So, in > xen_ram_init, user_lowmem is not 0. Ah, I see. We do the split calculation twice on xen. That is pretty pointless. New patch attached. cheers, Gerd From a1bb0d4f7a94e97102e7ea72d0a65de2a17b1160 Mon Sep 17 00:00:00 2001 From: Gerd Hoffmann Date: Thu, 23 Jun 2016 16:49:03 +0200 Subject: [PATCH] xen: fix ram init regression Commit "8156d48 pc: allow raising low memory via max-ram-below-4g option" causes a regression on xen, because it uses a different memory split. This patch initializes max-ram-below-4g to zero and leaves the initialization to the memory initialization functions. That way they can pick different default values (max-ram-below-4g is zero still) or use the user supplied value (max-ram-below-4g is non-zero). Also skip the whole ram split calculation on Xen. xen_ram_init() does its own split calculation anyway so it is superfluous, also this way xen_ram_init can actually see whenever max-ram-below-4g is zero or not. Signed-off-by: Gerd Hoffmann --- hw/i386/pc.c | 2 +- hw/i386/pc_piix.c | 52 +++++++++++++++++++++++++++++----------------------- hw/i386/pc_q35.c | 3 +++ xen-hvm.c | 3 +++ 4 files changed, 36 insertions(+), 24 deletions(-) diff --git a/hw/i386/pc.c b/hw/i386/pc.c index 7198ed5..66e1dae 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -1886,7 +1886,7 @@ static void pc_machine_initfn(Object *obj) pc_machine_get_hotplug_memory_region_size, NULL, NULL, NULL, &error_abort); - pcms->max_ram_below_4g = 0xe0000000; /* 3.5G */ + pcms->max_ram_below_4g = 0; /* use default */ 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 53bc968..f51fa77 100644 --- a/hw/i386/pc_piix.c +++ b/hw/i386/pc_piix.c @@ -108,37 +108,43 @@ static void pc_init1(MachineState *machine, * so legacy non-PAE guests can get as much memory as possible in * the 32bit address space below 4G. * + * - Note that Xen has its own ram setp code in xen_ram_init(), + * called via xen_hvm_init(). + * * 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) */ - 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); - } - } - } - - if (machine->ram_size >= lowmem) { - pcms->above_4g_mem_size = machine->ram_size - lowmem; - pcms->below_4g_mem_size = lowmem; - } else { - pcms->above_4g_mem_size = 0; - pcms->below_4g_mem_size = machine->ram_size; - } - if (xen_enabled()) { xen_hvm_init(pcms, &ram_memory); + } else { + if (!pcms->max_ram_below_4g) { + pcms->max_ram_below_4g = 0xe0000000; /* default: 3.5G */ + } + 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); + } + } + } + + if (machine->ram_size >= lowmem) { + pcms->above_4g_mem_size = machine->ram_size - lowmem; + pcms->below_4g_mem_size = lowmem; + } else { + pcms->above_4g_mem_size = 0; + pcms->below_4g_mem_size = machine->ram_size; + } } pc_cpus_init(pcms); diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c index e4b541f..1b653e2 100644 --- a/hw/i386/pc_q35.c +++ b/hw/i386/pc_q35.c @@ -93,6 +93,9 @@ static void pc_q35_init(MachineState *machine) /* Handle the machine opt max-ram-below-4g. It is basically doing * min(qemu limit, user limit). */ + if (!pcms->max_ram_below_4g) { + pcms->max_ram_below_4g = 1ULL << 32; /* default: 4G */; + } if (lowmem > pcms->max_ram_below_4g) { lowmem = pcms->max_ram_below_4g; if (machine->ram_size - lowmem > lowmem && diff --git a/xen-hvm.c b/xen-hvm.c index 98ea44f..eb57792 100644 --- a/xen-hvm.c +++ b/xen-hvm.c @@ -190,6 +190,9 @@ static void xen_ram_init(PCMachineState *pcms, /* Handle the machine opt max-ram-below-4g. It is basically doing * min(xen limit, user limit). */ + if (!user_lowmem) { + user_lowmem = HVM_BELOW_4G_RAM_END; /* default */ + } if (HVM_BELOW_4G_RAM_END <= user_lowmem) { user_lowmem = HVM_BELOW_4G_RAM_END; } -- 1.8.3.1