Memory hotplug fails with ACPI error message

This document (7015086) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 11 Service Pack 1 (SLES 11 SP1)
SUSE Linux Enterprise Server 11 Service Pack 2 (SLES 11 SP2)
SUSE Linux Enterprise Server 11 Service Pack 3 (SLES 11 SP3)
SUSE Linux Enterprise Server 11 Service Pack 4 (SLES 11 SP4)

SUSE Linux Enterprise Server 12

Situation

Attempting to hot-add memory to a SLES 11/12 system, for example running as a VMware 5.1 guest, fails with kernel error messages similar to these:

kworker/0:0: page allocation failure: order:9, mode:0x80d0
[..kernel trace..]
API:memory_hp:add_memory failed
ACPI:memory_hp:Error in acpi_memory_enable_device
acpi_memhotplug: probe of PNP0C80:00 failed with error -22

Subsequently, the additional memory does not get attached.

Resolution

Provision enough memory to not depend on memory hotplug prior to starting a Linux system.

Cause

On tight memory, the Linux kernel is unable to allocate enough space for the new Page Medium Directory (PMD), which has to be 2 MB of continuous memory on x86-64 architecture. In this situation, it is not possible to hotplug more memory to the Linux system.

Additional Information

Depending on the workload of the system, running

sync
echo 3 > /proc/sys/vm/drop_caches

before attempting to attach memory may free up enough space for the operation to succeed, but it is unreliable and may temporarily have adverse impact on system performance.

As a reliable alternative to memory hot plugging on VMware virtualization products it is recommend to use ballooning instead, as described in chapter 3.3 of the Understanding Memory Resource Management in VMware ESX Server whitepaper by VMware.

Disclaimer

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