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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Re: [Xen-users] Max. PV and HVM Guests
>>> On 2009/11/09 at 05:05, Pasi Kärkkäinen<pasik@xxxxxx> wrote: > On Mon, Nov 09, 2009 at 08:01:00PM +0800, Mr. Teo En Ming (Zhang Enming) > wrote: >> No, I didn't limit dom0 memory in grub.conf. >> > > You should. Really? I thought current conventional wisdom was to allow Xen to self-manage memory in both dom0 and domUs, and not to manually adjust this? I run several Xen systems with anywhere from 8 to 24 GB of RAM and 20 to 30 domUs on some of these systems and have *never* specified the dom0 memory at boot time - the Xen ballooning has always functioned perfectly fine, and never crashed my dom0. Furthermore, while I'm not Linux developer and so not familiar with how Linux calculates buffering and caching, I do know that my Linux systems dynamically manage buffers and caches, and when memory is reduced or some application requires a larger amount of physical memory, Linux reduces the amount of data in buffers and caches. Of course, a lot of this depends on what you're doing in dom0 - on my Xen servers, my dom0 is strictly for Xen management - I'm not running anything else in dom0 that would require large amounts of memory, memory buffers and caches, etc. -Nick > > If dom0 has all the memory at boot time, you need to balloon down dom0 > memory every time you create a new guest - this can (and will) cause > problems with the dom0 linux kernel. > > Linux calculates some internal parameters/buffers/values based on the > _boot time_ amount of memory. And when the amount of memory goes down to > only a small fraction of that while creating new guests bad things can > happen.. > > It still shouldn't crash though.. I bet your problem will get fixed when > you limit the dom0 memory to say dom0_mem=512M and reboot. > > -- Pasi > >> Here's my xm info output after I have shutdown all the virtual machines. >> >> [root@fedora11-x86-64-host ~]# xm list >> Name ID Mem VCPUs State >> Time(s) >> Domain-0 0 2812 2 r----- >> 3242.5 >> [root@fedora11-x86-64-host ~]# xm info >> host : fedora11-x86-64-host >> release : 2.6.30-rc3-enming.teo-tip >> version : #1 SMP Wed Aug 19 23:14:15 SGT 2009 >> machine : x86_64 >> nr_cpus : 2 >> nr_nodes : 1 >> cores_per_socket : 2 >> threads_per_core : 1 >> cpu_mhz : 2800 >> hw_caps : >> bfebfbff:20100800:00000000:00000140:0400e3bd:00000000:00000001:00000000 >> virt_caps : hvm hvm_directio >> total_memory : 6039 >> free_memory : 3124 >> node_to_cpu : node0:0-1 >> node_to_memory : node0:3124 >> xen_major : 3 >> xen_minor : 5 >> xen_extra : -unstable >> xen_caps : xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32 >> hvm-3.0-x86_32p hvm-3.0-x86_64 >> xen_scheduler : credit >> xen_pagesize : 4096 >> platform_params : virt_start=0xffff800000000000 >> xen_changeset : Tue Sep 01 11:34:31 2009 +0100 > 20143:a7de5bd776ca >> xen_commandline : iommu=1 >> cc_compiler : gcc version 4.4.1 20090725 (Red Hat 4.4.1-2) >> (GCC) >> cc_compile_by : root >> cc_compile_domain : (none) >> cc_compile_date : Thu Sep 10 07:01:13 SGT 2009 >> xend_config_format : 4 >> >> -- >> Mr. Teo En Ming (Zhang Enming) Dip(Mechatronics) BEng(Hons)(Mechanical >> Engineering) >> Alma Maters: >> (1) Singapore Polytechnic >> (2) National University of Singapore >> My Primary Blog: [1]http://teo-en-ming-aka-zhang-enming.blogspot.com >> My Secondary Blog: [2]http://enmingteo.wordpress.com >> My Youtube videos: [3]http://www.youtube.com/user/enmingteo >> Email: [4]space.time.universe@xxxxxxxxx >> Mobile Phone (Starhub Prepaid): +65-8369-2618 >> Street: Bedok Reservoir Road >> Country: Singapore >> >> On Mon, Nov 9, 2009 at 7:54 PM, Pasi Kärkkäinen <[5]pasik@xxxxxx> wrote: >> >> On Mon, Nov 09, 2009 at 06:52:37PM +0800, Mr. Teo En Ming (Zhang > Enming) >> wrote: >> > Hi, >> > >> > Please watch this 4-minute video at >> > [1][6]http://www.youtube.com/watch?v=LbLaPpwNAx4 >> > >> > I have only started 3 HVM Linux guests with 1 GB ram each. I can't >> start >> > the 4th HVM guest. If I attempt to start the 4th instance, it will >> crash >> > dom0. >> > >> > Are there anything in the xm dmesg output that could explain the >> low limit >> > to the number of VMs that I could start before dom0 becomes >> unresponsive? >> > >> >> Have you limited dom0 memory (by specifying dom0_mem=XMB option in >> grub.conf for xen.gz) ? >> >> What does "xm info" say about free memory before starting any guests? >> -- Pasi >> >> References >> >> Visible links >> 1. http://teo-en-ming-aka-zhang-enming.blogspot.com/ >> 2. http://enmingteo.wordpress.com/ >> 3. http://www.youtube.com/user/enmingteo >> 4. mailto:space.time.universe@xxxxxxxxx >> 5. mailto:pasik@xxxxxx >> 6. http://www.youtube.com/watch?v=LbLaPpwNAx4 -------- This e-mail may contain confidential and privileged material for the sole use of the intended recipient. 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