Mailing List Archive: kernel log flooded with: xen balloon: reserve additional memory: add memory() failed: -17

Hi,

I have encountered an apparently benign error on two systems where the
dom0 kernel log is flooded with messages like:

[52482.163855] System RAM resource [mem 0x1b8000000-0x1bfffffff] cannot
be added
[52482.163860] xen_balloon: reserve_additional_memory: add_memory()
failed: -17

The first line is from drivers/xen/xen-balloon.c, the second from
mm/memory_hotplug.c

The trigger for the messages seems to be the first occasion that a Xen
guest is shutdown. I have noted this in a vanilla 3.6.7 and kernel
3.5.0-18 built from Ubuntu sources. Xen version is 4.2.0. It is not
clear why the dom0 is kernel is trying to balloon up as the Xen command
line is specifies a fixed dom0 memory allocation and noselfballooning is
specified for the kernel and ballooning is also disabled in the
xend-config.sxp / xl.conf (one system using xm, another xl)

xen command line:
placeholder xsave=0 iommu=0 console=vga,com2 com2=115200,8n1
dom0_mem=max:6144m

kernel command line:
root=/dev/loop0 ro console=tty1 console=hvc0 earlyprintk=xen nomodeset
noselfballooning

Examining /proc/iomem does show that the dom0 memory allocation is
actually 64kb short of 6144Mb:

cat /proc/iomem | grep System\ RAM
00010000-0009bfff : System RAM [573440 bytes]
00100000-cb2dffff : System RAM [3407740928 bytes]
100000000-1b4d83fff : System RAM [3034071040 bytes]

Total system ram: 6442385408 - 6x2^30 = 65536

The memory range indicated in the log message is "Unusable memory" in
/proc/iomem:
1b4d84000-82fffffff : Unusable memory

Another point of interest is that we have multiple "identical" hardware
platforms (Dell T320) for the system running the 3.5.0-18 kernel but
only see this error on a slightly more recent system. Older systems
show in /proc/iomem that all memory is System RAM.

100000000-82fffffff : System RAM [older system BIOS 1.0]

100000000-1b4d83fff : System RAM [newer system BIOS 1.3]
1b4d84000-82fffffff : Unusable memory

The BIOS revision between the old and new has changed so I was
wondering if it is possible that there is a white list which affects the
impact of the kernel option:
CONFIG_X86_RESERVE_LOW=64
This is only a guess since the amount of memory reserved is equivalent
to the short fall calculated above. If this is the right area perhaps
the dom0 calculation for its memory entitlement needs to be taught to
not to try and hotplug the missing 64k when it has been reserved.

If any other information would be useful then please let me know.

Thanks,
James

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On 2012-12-19 08:47, James Dingwall wrote:
> Hi,
>
> I have encountered an apparently benign error on two systems where
> the dom0 kernel log is flooded with messages like:
>
> [52482.163855] System RAM resource [mem 0x1b8000000-0x1bfffffff]
> cannot be added
> [52482.163860] xen_balloon: reserve_additional_memory: add_memory()
> failed: -17
>
> The first line is from drivers/xen/xen-balloon.c, the second from
> mm/memory_hotplug.c
>
> The trigger for the messages seems to be the first occasion that a
> Xen guest is shutdown. I have noted this in a vanilla 3.6.7 and
> kernel 3.5.0-18 built from Ubuntu sources. Xen version is 4.2.0. It
> is not clear why the dom0 is kernel is trying to balloon up as the
> Xen
> command line is specifies a fixed dom0 memory allocation and
> noselfballooning is specified for the kernel and ballooning is also
> disabled in the xend-config.sxp / xl.conf (one system using xm,
> another xl)
>
> xen command line:
> placeholder xsave=0 iommu=0 console=vga,com2 com2=115200,8n1
> dom0_mem=max:6144m
>
> kernel command line:
> root=/dev/loop0 ro console=tty1 console=hvc0 earlyprintk=xen
> nomodeset noselfballooning
>
> Examining /proc/iomem does show that the dom0 memory allocation is
> actually 64kb short of 6144Mb:
>
> cat /proc/iomem | grep System\ RAM
> 00010000-0009bfff : System RAM [573440 bytes]
> 00100000-cb2dffff : System RAM [3407740928 bytes]
> 100000000-1b4d83fff : System RAM [3034071040 bytes]
>
> Total system ram: 6442385408 - 6x2^30 = 65536
>
> The memory range indicated in the log message is "Unusable memory" in
> /proc/iomem:
> 1b4d84000-82fffffff : Unusable memory
>
> Another point of interest is that we have multiple "identical"
> hardware platforms (Dell T320) for the system running the 3.5.0-18
> kernel but only see this error on a slightly more recent system.
> Older systems show in /proc/iomem that all memory is System RAM.
>
> 100000000-82fffffff : System RAM [older system BIOS 1.0]
>
> 100000000-1b4d83fff : System RAM [newer system BIOS 1.3]
> 1b4d84000-82fffffff : Unusable memory
>
> The BIOS revision between the old and new has changed so I was
> wondering if it is possible that there is a white list which affects
> the impact of the kernel option:
> CONFIG_X86_RESERVE_LOW=64
> This is only a guess since the amount of memory reserved is
> equivalent to the short fall calculated above. If this is the right
> area perhaps the dom0 calculation for its memory entitlement needs to
> be taught to not to try and hotplug the missing 64k when it has been
> reserved.
>
> If any other information would be useful then please let me know.

With some further investigation we have determined that the different
BIOS version does not seem to be a factor and the key point is actually
the Xen command line. The reason that we had max: specified is that
without it we could not boot the kernel/xen combination on an AMD
platform. I will do some further testing to see what the result of
dom0_mem=6144m,max:6144m as suggested
http://wiki.xen.org/wiki/Xen_Best_Practices gets us.

placeholder xsave=0 iommu=0 console=vga,com2 com2=115200,8n1
dom0_mem=max:6144m
results in /proc/iomem having an unusable range and top reports
6083900k of memory in dom0

placeholder xsave=0 iommu=0 console=vga,com2 com2=115200,8n1
dom0_mem=6144m
no unusable range, top reports 5605976k of memory in dom0 and no log
messages

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