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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 30 Sep 2019 08:10:01 +0100 Received: from d06av25.portsmouth.uk.ibm.com (d06av25.portsmouth.uk.ibm.com [9.149.105.61]) by b06avi18626390.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x8U79VKV23396832 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 30 Sep 2019 07:09:31 GMT Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1191B11C05C; Mon, 30 Sep 2019 07:10:00 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BC91711C04A; Mon, 30 Sep 2019 07:09:59 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.152.224.146]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 30 Sep 2019 07:09:59 +0000 (GMT) Subject: Re: [PATCH v7 4/4] s390: do not call memory_region_allocate_system_memory() multiple times To: Peter Xu , Igor Mammedov References: <20190924144751.24149-1-imammedo@redhat.com> <20190924144751.24149-5-imammedo@redhat.com> <20190925032700.GI28074@xz-x1> <20190925135105.6e5f249a@redhat.com> <20190925235235.GV28074@xz-x1> <20190927153320.2edc683c@redhat.com> <20190928012808.GA31218@xz-x1> From: Christian Borntraeger Openpgp: preference=signencrypt Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190928012808.GA31218@xz-x1> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 19093007-0016-0000-0000-000002B1F59E X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19093007-0017-0000-0000-00003312CED8 Message-Id: <63e706b4-4a6a-3be5-6bb7-9c744d269d98@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-09-30_04:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1909300075 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [generic] [fuzzy] X-Received-From: 148.163.156.1 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: thuth@redhat.com, david@redhat.com, cohuck@redhat.com, qemu-devel@nongnu.org, qemu-s390x@nongnu.org, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 28.09.19 03:28, Peter Xu wrote: > On Fri, Sep 27, 2019 at 03:33:20PM +0200, Igor Mammedov wrote: >> On Thu, 26 Sep 2019 07:52:35 +0800 >> Peter Xu wrote: >> >>> On Wed, Sep 25, 2019 at 01:51:05PM +0200, Igor Mammedov wrote: >>>> On Wed, 25 Sep 2019 11:27:00 +0800 >>>> Peter Xu wrote: >>>> >>>>> On Tue, Sep 24, 2019 at 10:47:51AM -0400, Igor Mammedov wrote: >>>>>> s390 was trying to solve limited KVM memslot size issue by abusing >>>>>> memory_region_allocate_system_memory(), which breaks API contract >>>>>> where the function might be called only once. >>>>>> >>>>>> Beside an invalid use of API, the approach also introduced migration >>>>>> issue, since RAM chunks for each KVM_SLOT_MAX_BYTES are transferred in >>>>>> migration stream as separate RAMBlocks. >>>>>> >>>>>> After discussion [1], it was agreed to break migration from older >>>>>> QEMU for guest with RAM >8Tb (as it was relatively new (since 2.12) >>>>>> and considered to be not actually used downstream). >>>>>> Migration should keep working for guests with less than 8TB and for >>>>>> more than 8TB with QEMU 4.2 and newer binary. >>>>>> In case user tries to migrate more than 8TB guest, between incompatible >>>>>> QEMU versions, migration should fail gracefully due to non-exiting >>>>>> RAMBlock ID or RAMBlock size mismatch. >>>>>> >>>>>> Taking in account above and that now KVM code is able to split too >>>>>> big MemorySection into several memslots, partially revert commit >>>>>> (bb223055b s390-ccw-virtio: allow for systems larger that 7.999TB) >>>>>> and use kvm_set_max_memslot_size() to set KVMSlot size to >>>>>> KVM_SLOT_MAX_BYTES. >>>>>> >>>>>> 1) [PATCH RFC v2 4/4] s390: do not call memory_region_allocate_system_memory() multiple times >>>>>> >>>>>> Signed-off-by: Igor Mammedov >>>>> >>>>> Acked-by: Peter Xu >>>>> >>>>> IMHO it would be good to at least mention bb223055b9 in the commit >>>>> message even if not with a "Fixed:" tag. May be amended during commit >>>>> if anyone prefers. >>>> >>>> /me confused, bb223055b9 is mentioned in commit message >>> >>> I'm sorry, I overlooked that. >>> >>>> >>>>> Also, this only applies the split limitation to s390. Would that be a >>>>> good thing to some other archs as well? >>>> >>>> Don't we have the similar bitmap size issue in KVM for other archs? >>> >>> Yes I thought we had. So I feel like it would be good to also allow >>> other archs to support >8TB mem as well. Thanks, >> Another question, Is there another archs with that much RAM that are >> available/used in real life (if not I'd wait for demand to arise first)? > > I don't know, so it was a pure question besides the series. Sorry if > that holds your series somehow, it was not my intention. > >> >> If we are to generalize it to other targets, then instead of using >> arbitrary memslot max size per target, we could just hardcode or get >> from KVM, max supported size of bitmap and use that to calculate >> kvm_max_slot_size depending on target page size. > > Right, I think if so hard code would be fine for now, and probably can > with a smallest one across all archs (should depend on the smallest > page size, I guess). > >> >> Then there wouldn't be need for having machine specific code >> to care about it and pick/set arbitrary values. >> >> Another aspect to think about if we are to enable it for >> other targets is memslot accounting. It doesn't affect s390 >> but other targets that support memory hotplug now assume 1:1 >> relation between memoryregion:memslot, which currently holds >> true but would need to amended in case split is enabled there. > > I didn't know this. So maybe it makes more sense to have s390 only > here. Thanks, OK. So shall I take the series as is via the s390 tree? I would like to add the following patch on top if nobody minds: Subject: [PATCH 1/1] s390/kvm: split kvm mem slots at 4TB Instead of splitting at an unaligned address, we can simply split at 4TB. Signed-off-by: Christian Borntraeger --- target/s390x/kvm.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c index ad2dd14f7e78..611f56f4b5ac 100644 --- a/target/s390x/kvm.c +++ b/target/s390x/kvm.c @@ -126,12 +126,11 @@ /* * KVM does only support memory slots up to KVM_MEM_MAX_NR_PAGES pages * as the dirty bitmap must be managed by bitops that take an int as - * position indicator. If we have a guest beyond that we will split off - * new subregions. The split must happen on a segment boundary (1MB). + * position indicator. This would end at an unaligned address + * (0x7fffff00000). As future variants might provide larger pages + * and to make all addresses properly aligned, let us split at 4TB. */ -#define KVM_MEM_MAX_NR_PAGES ((1ULL << 31) - 1) -#define SEG_MSK (~0xfffffULL) -#define KVM_SLOT_MAX_BYTES ((KVM_MEM_MAX_NR_PAGES * TARGET_PAGE_SIZE) & SEG_MSK) +#define KVM_SLOT_MAX_BYTES 4096UL*1024*1024*1024 static CPUWatchpoint hw_watchpoint; /* -- 2.21.0