Source: https://www.kernel.org/doc/Documentation/memory-hotplug.txt
How to online memory
--------------------
When the memory is hot-added, the kernel decides whether or not to "online"
it according to the policy which can be read from "auto_online_blocks" file::
% cat /sys/devices/system/memory/auto_online_blocks
The default depends on the CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
option. If it is disabled the default is "offline" which means the newly added
memory is not in a ready-to-use state and you have to "online" the newly added
memory blocks manually. Automatic onlining can be requested by writing "online"
to "auto_online_blocks" file::
% echo online > /sys/devices/system/memory/auto_online_blocks
This sets a global policy and impacts all memory blocks that will subsequently
be hotplugged.
If this is enabled by default then the following should achieve the same
goal as disabling the config option:
echo offline > /sys/devices/system/memory/auto_online_blocks
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https://bugs.launchpad.net/bugs/2028158
Title:
[SRU] Duplicate Device_dax ids Created and hence Probing is Failing.
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Jammy:
Fix Released
Status in linux source package in Lunar:
Fix Released
Status in linux source package in Mantic:
Fix Released
Bug description:
[Impact]
Description of problem:
Observed device_dax related probe errors in dmesg when HBM CPU is set
to flat mode. Duplicate device_dax ids were created and hence probing
is failing.
How reproducible:
Frequently
Version-Release
Release: 22.04.2, 22.10
[Test Case]
Steps to Reproduce:
1. Set HBM cpu to flat mode in memory settings in BIOS.
2. Boot to the OS.
3. Perform OS warm boot cycle test.
4. Observe the dax2.0/dax3.0/dax4.0/dax5.0 probe error.
Actual results:
Observed device_dax related errors in dmesg, device Dax is creating
dummy/duplicate devices and probe failing.
Expected results:
Dummy/duplicate devices should not create.
[Fix]
Upstream Fix
https://lore.kernel.org/linux-mm/166890823379.4183293.15333502171004313377.st...@dwillia2-xfh.jf.intel.com/T/
[Where problems could occur]
[Other Info]
https://code.launchpad.net/~mreed8855/ubuntu/+source/linux/+git/jammy/+ref/lp_2028158_device_dax_2
Additional info:
SUT is having 2*32C HBM cpus. Eligible system-ram mode change devices should
be only 2[dax0.0, dax1.0], but under "daxctl list -u" is showing 1st time 4
devices [dax0.0, 1.0, 2.0, 3.0], 2 is "state":"disabled" and 2 more devices is
"mode":"devdax" which are actuall devadax to system-ram convertible devices.
After reconfigure-device dax0.0, dax1.0 when you list the devices couple of
more dummy/dumplicate devices are creating with "state":"disabled"[Ex: dax4.0,
5.0 etc..].
root@ubuntu:/home/ubuntu# daxctl list -u
[
{
"chardev":"dax1.0",
"size":"64.00 GiB (68.72 GB)",
"target_node":3,
"align":2097152,
"mode":"devdax"---------------> HBM CPU 1, This we can change the devdax
to
system-ram
},
{
"chardev":"dax2.0",
"size":"64.00 GiB (68.72 GB)",
"target_node":2, --------------------> Duplicate device
"align":2097152,
"mode":"devdax",
"state":"disabled"
},
{
"chardev":"dax3.0",
"size":"64.00 GiB (68.72 GB)",
"target_node":3, --------------------> Duplicate device
"align":2097152,
"mode":"devdax",
"state":"disabled"
},
{
"chardev":"dax0.0",
"size":"64.00 GiB (68.72 GB)",
"target_node":2,
"align":2097152,
"mode":"devdax" ---------------> HBM CPU 1, This we can change the devdax
to
system-ram
}
]
root@ubuntu:/home/ubuntu# dmesg | grep -i error
[ 12.748884] device_dax: probe of dax2.0 failed with error -16
[ 12.748902] device_dax: probe of dax3.0 failed with error -16
After reconfig-device devdax to system-ram below are the results:
-------------------------------------------------------------------
root@ubuntu:/home/ubuntu# daxctl reconfigure-device -m system-ram dax0.0 -u
{
"chardev":"dax0.0",
"size":"64.00 GiB (68.72 GB)",
"target_node":2,
"align":2097152,
"mode":"system-ram",
"online_memblocks":32,
"total_memblocks":32,
"movable":true
}
reconfigured 1 device
root@ubuntu:/home/ubuntu# daxctl reconfigure-device -m system-ram dax1.0 -u
{
"chardev":"dax1.0",
"size":"64.00 GiB (68.72 GB)",
"target_node":3,
"align":2097152,
"mode":"system-ram",
"online_memblocks":32,
"total_memblocks":32,
"movable":true
}
reconfigured 1 device
root@ubuntu:/home/ubuntu# daxctl list -u
[
{
"chardev":"dax4.0",
"size":"64.00 GiB (68.72 GB)",
"target_node":2, --------------------> Duplicate device
"align":2097152,
"mode":"devdax",
"state":"disabled"
},
{
"chardev":"dax1.0",
"size":"64.00 GiB (68.72 GB)",
"target_node":3,
"align":2097152,
"mode":"system-ram",-----------> Converted from devdax - system-ram
"online_memblocks":32,
"total_memblocks":32,
"movable":true
},
{
"chardev":"dax5.0",
"size":"64.00 GiB (68.72 GB)",
"target_node":3, --------------------> Duplicate device
"align":2097152,
"mode":"devdax",
"state":"disabled"
},
{
"chardev":"dax2.0",
"size":"64.00 GiB (68.72 GB)",
"target_node":2, --------------------> Duplicate device
"align":2097152,
"mode":"devdax",
"state":"disabled"
},
{
"chardev":"dax3.0",
"size":"64.00 GiB (68.72 GB)",
"target_node":3, --------------------> Duplicate device
"align":2097152,
"mode":"devdax",
"state":"disabled"
},
{
"chardev":"dax0.0",
"size":"64.00 GiB (68.72 GB)",
"target_node":2,
"align":2097152,
"mode":"system-ram", -----------> Converted from devdax - system-ram
"online_memblocks":32,
"total_memblocks":32,
"movable":true
}
]
root@ubuntu:/home/ubuntu# dmesg | grep -i dax
[ 12.748880] device_dax dax2.0: mapping0: 0x2080000000-0x307fffffff could
not reserve range
[ 12.748884] device_dax: probe of dax2.0 failed with error -16
[ 12.748901] device_dax dax3.0: mapping0: 0x5080000000-0x607fffffff could
not reserve range
[ 12.748902] device_dax: probe of dax3.0 failed with error -16
[ 812.677056] device_dax dax4.0: mapping0: 0x2080000000-0x307fffffff could
not reserve range
[ 812.677070] device_dax: probe of dax4.0 failed with error -16
[ 821.092762] device_dax dax5.0: mapping0: 0x5080000000-0x607fffffff could
not reserve range
[ 821.092774] device_dax: probe of dax5.0 failed with error -16
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