On Fri, Nov 06, 2009 at 03:59:04PM +0300, Alexander Kobernik
wrote:> Hi everybody,
>
> there is physical box with 32GB of RAM installed on it.
> DomU domains aren''t not launched yet. Here''s output of
''xm list'' command:
>
> Name ID Mem VCPUs State Time(s)
> Domain-0 0 512 8 r----- 107900.3
>
> So, there''s only Dom0 there. Here''s output of
''free -m'' command:
>
> total used free shared buffers cached
> Mem: 512 378 133 0 53 90
> -/+ buffers/cache: 234 277
> Swap: 2047 0 2047
>
> Thus free/available memory (for DomUs) should be equal to something
like:
>
> 32GB - 512MB = 32256MB = 33030144KB
>
> However, according to Xen, there are about 31791MB of free memory only.
>
> Here''s output of ''xm info'' command:
>
> host : xxx
> release : 2.6.18-92.1.6.el5xen
> version : #1 SMP Wed Jun 25 14:13:10 EDT 2008
> machine : x86_64
> nr_cpus : 8
> nr_nodes : 1
> cores_per_socket : 4
> threads_per_core : 1
> cpu_mhz : 2660
> hw_caps :
> bfebfbff:20100800:00000000:00000140:040ce3bd:00000000:00000001:00000000
> virt_caps : hvm
> total_memory : 32762
> free_memory : 31791
> node_to_cpu : node0:0-7
> node_to_memory : node0:31791
> xen_major : 3
> xen_minor : 3
> xen_extra : .0
> 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 : unavailable
> cc_compiler : gcc version 4.1.2 20071124 (Red Hat 4.1.2-42)
> cc_compile_by : root
> cc_compile_domain : xxx
> cc_compile_date : Tue Sep 9 20:18:14 CEST 2008
> xend_config_format : 4
>
> Here''s reduced output of ''xm top'' command:
>
> xentop - 12:51:59 Xen 3.3.0
> 1 domains: 1 running, 0 blocked, 0 paused, 0 crashed, 0 dying, 0
shutdown
> Mem: 33549248k total, 995128k used, 32554120k free CPUs: 8 @ 2660MHz
>
> NAME STATE CPU(sec) CPU(%) MEM(k) MEM(%) MAXMEM(k) MAXMEM(%)
> Domain-0 -----r 107963 0.0 524288 1.6 no limit n/a
>
> So, could someone explain who allocated/cached 465MB (32256MB - 31791MB)
> of RAM?
>
Xen hypervisor uses some memory, but not that much. The rest goes for
some DMA memory reservations etc.
-- Pasi
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