Re: [Bug fix PATCH 2/2] acpi, movablemem_map: Make whatever nodesthe kernel resides in un-hotpluggable.

[Tang Chen]

On 02/24/2013 03:26 AM, Rob Landley wrote:
> On 02/20/2013 05:00:56 AM, Tang Chen wrote:
> > There could be several memory ranges in the node in which the kernel
> > resides.
> > When using movablemem_map=acpi, we may skip one range that have memory
> > reserved
> > by memblock. But if it is too small, then the kernel will fail to
> > boot. So, make
> > the whole node which the kernel resides in un-hotpluggable. Then the
> > kernel has
> > enough memory to use.
> >
> > Reported-by: H Peter Anvin <hpa@xxxxxxxxx>
> > Signed-off-by: Tang Chen <tangchen@xxxxxxxxxxxxxx>
>
> Docs part Acked-by: Rob Landley <rob@xxxxxxxxxxx> (with minor
> non-blocking snark).

Hi Rob,

Thanks for ack. :)

> > @@ -1673,6 +1675,10 @@ bytes respectively. Such letter suffixes can
> > also be entirely omitted.
> > satisfied. So the administrator should be careful that
> > the amount of movablemem_map areas are not too large.
> > Otherwise kernel won't have enough memory to start.
> > + NOTE: We don't stop users specifying the node the
> > + kernel resides in as hotpluggable so that this
> > + option can be used as a workaround of firmware
> > + bugs.
>
> I usually see workaround "for", not "of". And your whitespace is
> inconsistent on that last line.
>
> And I'm now kind of curious what such a workaround would accomplish, but
> I'm suspect it's obvious to people who wind up needing it.

SFAIK, this is more useful when debugging.

> > MTD_Partition= [MTD]
> > Format: <name>,<region-number>,<size>,<offset>
> > diff --git a/arch/x86/mm/srat.c b/arch/x86/mm/srat.c
> > index b8028b2..79836d0 100644
> > --- a/arch/x86/mm/srat.c
> > +++ b/arch/x86/mm/srat.c
> > @@ -166,6 +166,9 @@ handle_movablemem(int node, u64 start, u64 end,
> > u32 hotpluggable)
> > * for other purposes, such as for kernel image. We cannot prevent
> > * kernel from using these memory, so we need to exclude these memory
> > * even if it is hotpluggable.
> > + * Furthermore, to ensure the kernel has enough memory to boot, we make
> > + * all the memory on the node which the kernel resides in
> > + * un-hotpluggable.
> > */
>
> Can you hot-unplug half a node? (Do you have a choice with the
> granularity here?)

No, we cannot hot-plug/hot-unplug half a node. But we can offline some 
of the
memory, not all the memory on one node. :)

Here, hotplug means finally you will physically remove the hardware 
device from
the system while the system is running. So there is no such thing like 
hotplug
half a node, I think. :)

Thanks. :)
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