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[Xen-users] hypervisor memory usage

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] hypervisor memory usage
From: Vladimir Zidar <mr_w@xxxxxxxxxxxxx>
Date: Tue, 27 Oct 2009 11:36:59 +0100
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I'm wondering why hypervisor itself uses so much memory? Is it normal?

I have several servers with 8GB of ram, all of them running x86_64 centos 5.4 (latest) and when running under xen, dom0 has
[root@palmae ~]# head -4 /proc/meminfo
MemTotal:      7661568 kB
MemFree:       6550044 kB
Buffers:         37400 kB
Cached:         303480 kB

Which is  440MB less than what I get without xen.
It comes down to what amount of memory kernel gets either from Xen or from BIOS. Please note the differences:

when run under xen:
BIOS-provided physical RAM map:
Xen: 0000000000000000 - 00000001dc25c000 (usable)
On node 0 totalpages: 1950300

and just bare metal linux:
BIOS-provided physical RAM map:
BIOS-e820: 0000000000010000 - 000000000009ec00 (usable)
BIOS-e820: 000000000009ec00 - 00000000000a0000 (reserved)
BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)
BIOS-e820: 0000000000100000 - 00000000bf780000 (usable)
BIOS-e820: 00000000bf780000 - 00000000bf78e000 (ACPI data)
BIOS-e820: 00000000bf78e000 - 00000000bf7d0000 (ACPI NVS)
BIOS-e820: 00000000bf7d0000 - 00000000bf7e0000 (reserved)
BIOS-e820: 00000000bf7ec000 - 00000000c0000000 (reserved)
BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved)
BIOS-e820: 00000000ffc00000 - 0000000100000000 (reserved)
BIOS-e820: 0000000100000000 - 0000000240000000 (usable)
DMI present.
ACPI: RSDP (v000 ACPIAM ) @ 0x00000000000fa460 ACPI: RSDT (v001 7522MS A7522800 0x20090903 MSFT 0x00000097) @ 0x00000000bf780000 ACPI: FADT (v001 7522MS A7522800 0x20090903 MSFT 0x00000097) @ 0x00000000bf780200 ACPI: MADT (v001 7522MS A7522800 0x20090903 MSFT 0x00000097) @ 0x00000000bf780390 ACPI: MCFG (v001 7522MS OEMMCFG 0x20090903 MSFT 0x00000097) @ 0x00000000bf780440 ACPI: OEMB (v001 7522MS A7522800 0x20090903 MSFT 0x00000097) @ 0x00000000bf78e040 ACPI: HPET (v001 7522MS OEMHPET 0x20090903 MSFT 0x00000097) @ 0x00000000bf78a480 ACPI: SSDT (v001 DpgPmm CpuPm 0x00000012 INTL 0x20051117) @ 0x00000000bf790350 ACPI: DSDT (v001 A7522 A7522800 0x00000800 INTL 0x20051117) @ 0x0000000000000000
No NUMA configuration found
Faking a node at 0000000000000000-0000000240000000
Bootmem setup node 0 0000000000000000-0000000240000000
Memory for crash kernel (0x0 to 0x0) notwithin permissible range
disabling kdump
On node 0 totalpages: 2061313

That is around 440MB.. It just doesn't seem normal to me? Anything to be tuned or checked or changed?

Kind Regards,

PS, I apologize if this was asked more than 10 times, but I haven't been able to google it out (poor choice of keywords maybe).

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