From mboxrd@z Thu Jan 1 00:00:00 1970 From: Igor Mammedov Date: Mon, 07 Sep 2015 14:31:31 +0000 Subject: Re: [Qemu-ppc] KVM memory slots limit on powerpc Message-Id: <20150907163131.3cb11a7b@nial.brq.redhat.com> List-Id: References: <55E965FC.8080909@redhat.com> <55E96B87.8020900@de.ibm.com> <55E96CB9.4070100@suse.de> In-Reply-To: <55E96CB9.4070100@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Alexander Graf Cc: Christian Borntraeger , Thomas Huth , kvm-ppc@vger.kernel.org, qemu-ppc@nongnu.org, kvm@vger.kernel.org, David Gibson , Alex Williamson , Bharata B Rao On Fri, 4 Sep 2015 12:04:41 +0200 Alexander Graf wrote: > > > On 04.09.15 11:59, Christian Borntraeger wrote: > > Am 04.09.2015 um 11:35 schrieb Thomas Huth: > >> > >> Hi all, > >> > >> now that we get memory hotplugging for the spapr machine on qemu-ppc, > >> too, it seems like we easily can hit the amount of KVM-internal memory > >> slots now ("#define KVM_USER_MEM_SLOTS 32" in > >> arch/powerpc/include/asm/kvm_host.h). For example, start > >> qemu-system-ppc64 with a couple of "-device secondary-vga" and "-m > >> 4G,slots2,maxmem@G" and then try to hot-plug all 32 DIMMs ... and > >> you'll see that it aborts way earlier already. > >> > >> The x86 code already increased the amount of KVM_USER_MEM_SLOTS to 509 > >> already (+3 internal slots = 512) ... maybe we should now increase the > >> amount of slots on powerpc, too? Since we don't use internal slots on > >> POWER, would 512 be a good value? Or would less be sufficient, too? > > > > When you are at it, the s390 value should also be increased I guess. > > That constant defines the array size for the memslot array in struct kvm > which in turn again gets allocated by kzalloc, so it's pinned kernel > memory that is physically contiguous. Doing big allocations can turn > into problems during runtime. > > So maybe there is another way? Can we extend the memslot array size > dynamically somehow? Allocate it separately? How much memory does the > memslot array use up with 512 entries? KVM switched memslots allocation to kvm_kvzalloc(), so it would fallback to vmalloc commit 744961341d472db6272ed9b42319a90f5a2aa7c4 kvm: avoid page allocation failure in kvm_set_memory_region() > > Alex > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html