Re: [RFC PATCH 0/2] arm64: memory-hotplug: Add Memory Hotplug support

[Scott Branden]

Hi Xishi,

Thanks for the reply - please see comments below.

On 16-12-01 05:49 PM, Xishi Qiu wrote:
> On 2016/12/2 8:19, Scott Branden wrote:
>
> > This patchset is sent for comment to add memory hotplug support for ARM64
> > based platforms.  It follows hotplug code added for other architectures
> > in the linux kernel.
> >
> > I tried testing the memory hotplug feature following documentation from
> > Documentation/memory-hotplug.txt.  I don't think it is working as expected
> > - see below:
> >
> > To add memory to the system I did the following:
> > echo 0x400000000 > /sys/devices/system/memory/probe
> >
> > The memory is displayed as system ram:
> > cat /proc/iomem:
> > 74000000-77ffffff : System RAM
> >   74080000-748dffff : Kernel code
> >   74950000-749d2fff : Kernel data
> > 400000000-43fffffff : System RAM
> >
> > But does not seem to be added to the kernel memory.
> > /proc/meminfo did not change.
> >
> > What else needs to be done so the memory is added to the kernel memory
> > pool for normal allocation?
>
> Hi Scott,
>
> Do you mean it still don't support hod-add after apply this patchset?

After applying the patch it appears to partially support hot-add. 
Please let me know if you think it is working as expected?

The memory probe functions in that the memory is registered with the 
system and shows up in /proc/iomem.  But, the memory is not available in 
/proc/meminfo.  Do you think something else needs to be adjusted for 
ARM64 to hotadd the memory

I just found another clue:
under /sys/devices/system/memory I only see one memory entry (before or 
after I try to hotadd additional memory).

/sys/devices/system/memory # ls
auto_online_blocks  memory0            uevent
block_size_bytes    probe

In arch/arm64/include/asm/sparsemem.h if I change SECTION_SIZE_BITS from 
30 to 28 and recompile I get the following:
/sys/devices/system/memory # ls
auto_online_blocks  memory7            uevent
block_size_bytes    probe


In arch/arm64/include/asm/sparsemem.h if I change SECTION_SIZE_BITS from 
30 to 27 and recompile I get the following:
/sys/devices/system/memory # ls
auto_online_blocks  memory14            uevent
block_size_bytes    probe

If looks to me like something is not working properly in the ARM64 
implementation.  I should expect to see multiple memoryX entries under 
/sys/devices/system/memory?



> Thanks,
> Xishi Qiu
>
> > Scott Branden (2):
> >   arm64: memory-hotplug: Add MEMORY_HOTPLUG, MEMORY_HOTREMOVE,
> >     MEMORY_PROBE
> >   arm64: defconfig: enable MEMORY_HOTPLUG config options
> >
> >  arch/arm64/Kconfig           | 10 ++++++++++
> >  arch/arm64/configs/defconfig |  3 +++
> >  arch/arm64/mm/init.c         | 42 ++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 55 insertions(+)