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SubjectRe: [Patch v2] mm/hotplug: Only respect mem= parameter during boot stage

On 10/12/19 7:44 pm, Baoquan He wrote:
> In commit 357b4da50a62 ("x86: respect memory size limiting via mem=
> parameter") a global varialbe global max_mem_size is added to store
typo ^^^
> the value parsed from 'mem= ', then checked when memory region is
> added. This truly stops those DIMM from being added into system memory
> during boot-time.
> However, it also limits the later memory hotplug functionality. Any
> memory board can't be hot added any more if its region is beyond the
> max_mem_size. System will print error like below:
> [ 216.387164] acpi PNP0C80:02: add_memory failed
> [ 216.389301] acpi PNP0C80:02: acpi_memory_enable_device() error
> [ 216.392187] acpi PNP0C80:02: Enumeration failure
> From document of 'mem= ' parameter, it should be a restriction during
> boot, but not impact the system memory adding/removing after booting.
> mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
> ...
> So fix it by also checking if it's during boot-time when restrict memory
> adding. Otherwise, skip the restriction.

The fix looks reasonable, but I don't get the use case. Booting with mem= is
generally a debug option, is this for debugging memory hotplug + limited memory?


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