From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Gross Subject: Re: [PATCHv1] xen/balloon: disable memory hotplug in PV guests Date: Wed, 18 Mar 2015 14:57:15 +0100 Message-ID: <5509843B.2080205@suse.com> References: <1425910200-17541-1-git-send-email-david.vrabel@citrix.com> <54FED833.1080609@citrix.com> <54FEF308.3090702@oracle.com> <5500544B.4020302@citrix.com> <550061F0.9030206@oracle.com> <55066B88.9040300@suse.com> <20150316100344.GV27971@olila.local.net-space.pl> <5506B115.8090804@suse.com> <5509553A.7030707@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1YYETH-0003YM-6p for xen-devel@lists.xenproject.org; Wed, 18 Mar 2015 13:57:19 +0000 In-Reply-To: <5509553A.7030707@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: David Vrabel , Daniel Kiper Cc: xen-devel@lists.xenproject.org, Boris Ostrovsky List-Id: xen-devel@lists.xenproject.org On 03/18/2015 11:36 AM, David Vrabel wrote: > On 16/03/15 10:31, Juergen Gross wrote: >> On 03/16/2015 11:03 AM, Daniel Kiper wrote: >>> On Mon, Mar 16, 2015 at 06:35:04AM +0100, Juergen Gross wrote: >>>> On 03/11/2015 04:40 PM, Boris Ostrovsky wrote: >>>>> On 03/11/2015 10:42 AM, David Vrabel wrote: >>>>>> On 10/03/15 13:35, Boris Ostrovsky wrote: >>>>>>> On 03/10/2015 07:40 AM, David Vrabel wrote: >>>>>>>> On 09/03/15 14:10, David Vrabel wrote: >>>>>>>>> Memory hotplug doesn't work with PV guests because: >>>>>>>>> >>>>>>>>> a) The p2m cannot be expanded to cover the new sections. >>>>>>>> Broken by 054954eb051f35e74b75a566a96fe756015352c8 (xen: switch to >>>>>>>> linear virtual mapped sparse p2m list). >>>>>>>> >>>>>>>> This one would be non-trivial to fix. We'd need a sparse set of >>>>>>>> vm_area's for the p2m or similar. >>>>>>>> >>>>>>>>> b) add_memory() builds page tables for the new sections which >>>>>>>>> means >>>>>>>>> the new pages must have valid p2m entries (or a BUG occurs). >>>>>>>> After some more testing this appears to be broken by: >>>>>>>> >>>>>>>> 25b884a83d487fd62c3de7ac1ab5549979188482 (x86/xen: set regions above >>>>>>>> the >>>>>>>> end of RAM as 1:1) included 3.16. >>>>>>>> >>>>>>>> This one can be trivially fixed by setting the new sections in >>>>>>>> the p2m >>>>>>>> to INVALID_P2M_ENTRY before calling add_memory(). >>>>>>> Have you tried 3.17? As I said yesterday, it worked for me (with 4.4 >>>>>>> Xen). >>>>>> No. But there are three bugs that prevent it from working in 3.16+ so >>>>>> I'm really not sure how you had a working in a 3.17 PV guest. >>>>> >>>>> This is what I have: >>>>> >>>>> [build@build-mk2 linux-boris]$ ssh root@tst008 cat >>>>> /mnt/lab/bootstrap-x86_64/test_small.xm >>>>> extra="console=hvc0 debug earlyprintk=xen " >>>>> kernel="/mnt/lab/bootstrap-x86_64/vmlinuz" >>>>> ramdisk="/mnt/lab/bootstrap-x86_64/initramfs.cpio.gz" >>>>> memory=1024 >>>>> maxmem = 4096 >>>>> vcpus=1 >>>>> maxvcpus=3 >>>>> name="bootstrap-x86_64" >>>>> on_crash="preserve" >>>>> vif = [ 'mac=00:0F:4B:00:00:68, bridge=switch' ] >>>>> vnc=1 >>>>> vnclisten="0.0.0.0" >>>>> disk=['phy:/dev/guests/bootstrap-x86_64,xvda,w'] >>>>> [build@build-mk2 linux-boris]$ ssh root@tst008 xl create >>>>> /mnt/lab/bootstrap-x86_64/test_small.xm >>>>> Parsing config from /mnt/lab/bootstrap-x86_64/test_small.xm >>>>> [build@build-mk2 linux-boris]$ ssh root@tst008 xl list |grep >>>>> bootstrap-x86_64 >>>>> bootstrap-x86_64 2 1024 1 >>>>> -b---- 5.4 >>>>> [build@build-mk2 linux-boris]$ ssh root@g-pvops uname -r >>>>> 3.17.0upstream >>>>> [build@build-mk2 linux-boris]$ ssh root@g-pvops dmesg|grep >>>>> paravirtualized >>>>> [ 0.000000] Booting paravirtualized kernel on Xen >>>>> [build@build-mk2 linux-boris]$ ssh root@g-pvops grep MemTotal >>>>> /proc/meminfo >>>>> MemTotal: 968036 kB >>>>> [build@build-mk2 linux-boris]$ ssh root@tst008 xl mem-set >>>>> bootstrap-x86_64 2048 >>>>> [build@build-mk2 linux-boris]$ ssh root@tst008 xl list |grep >>>>> bootstrap-x86_64 >>>>> bootstrap-x86_64 2 2048 1 >>>>> -b---- 5.7 >>>>> [build@build-mk2 linux-boris]$ ssh root@g-pvops grep MemTotal >>>>> /proc/meminfo >>>>> MemTotal: 2016612 kB >>>>> [build@build-mk2 linux-boris]$ >>>>> >>>>> >>>>>> >>>>>> Regardless, it definitely doesn't work now because of the linear p2m >>>>>> change. What do you want to do about this? >>>>> >>>>> Since backing out p2m changes is not an option I guess your patch is >>>>> the >>>>> only short-term alternative. >>>>> >>>>> But this still looks like a regression so perhaps Juergen can take a >>>>> look to see how it can be fixed. >>>> >>>> Hmm, the p2m list is allocated for the maximum memory size of the domain >>>> which is obtained from the hypervisor. In case of Dom0 it is read via >>>> XENMEM_maximum_reservation, for a domU it is based on the E820 memory >>>> map read via XENMEM_memory_map. >>>> >>>> I just tested it with a 4.0-rc1 domU kernel with 512MB initial memory >>>> and 4GB of maxmem. The E820 map looked like this: >>>> >>>> [ 0.000000] Xen: [mem 0x0000000000000000-0x000000000009ffff] usable >>>> [ 0.000000] Xen: [mem 0x00000000000a0000-0x00000000000fffff] reserved >>>> [ 0.000000] Xen: [mem 0x0000000000100000-0x00000000ffffffff] usable >>>> >>>> So the complete 4GB were included, like they should. The resulting p2m >>>> list is allocated in the needed size: >>>> >>>> [ 0.000000] p2m virtual area at ffffc90000000000, size is 800000 >>>> >>>> So what is your problem here? Can you post the E820 map and the p2m map >>>> info for your failing domain, please? >>> >>> If you use memory hotplug then maxmem is not a limit from guest kernel >>> point of view (host still must allow that operation but it is another >>> not related issue). The problem is that p2m must be dynamically >>> expendable >>> to support it. Earlier implementation supported that thing and memory >>> hotplug worked without any issue. >> >> Okay, now I get it. >> >> The problem with the earlier p2m implementation was that it was >> expendable to support only up to 512GB of RAM. So we need some way to >> tell the kernel how much virtual memory it should reserve for the p2m >> list if memory hotplug is enabled. We could: >> >> a) use a configurable maximum (e.g. for 512GB RAM as today) > > I would set the p2m virtual area to cover up to 512 GB (needs 1 GB of > virt space) for a 64-bit guest and up to 64 GB (needs 64 MB of virt > space) for a 32-bit guest. Are 64 GB for 32 bit guests a sensible default? This will need more than 10% of the available virtual kernel space (taking fixmap etc. into account). And a 64 GB sized 32 bit domain is hardly usable (you have to play dirty tricks to get it even running). I'd rather use a default of 4 GB which can be changed via a Kconfig option. For 64 bits the default of 512 GB is okay, but should be configurable as well. Juergen