Re: [RFC] arm64: mm: update max_pfn after memory hotplug

[David Hildenbrand]

On 27.09.21 19:22, Georgi Djakov wrote:
> On 9/24/2021 1:54 AM, Chris Goldsworthy wrote:
> > From: Sudarshan Rajagopalan <quic_sudaraja@xxxxxxxxxxx>
> >
> > After new memory blocks have been hotplugged, max_pfn and max_low_pfn
> > needs updating to reflect on new PFNs being hot added to system.
> >
> > Signed-off-by: Sudarshan Rajagopalan <quic_sudaraja@xxxxxxxxxxx>
> > Signed-off-by: Chris Goldsworthy <quic_cgoldswo@xxxxxxxxxxx>
>
> Thanks for the patch, Chris!
>
> With this patch, the data in /proc/kpageflags appears to be correct and
> memory tools like procrank work again on arm64 platforms.
>
> Tested-by: Georgi Djakov <quic_c_gdjako@xxxxxxxxxxx>
>
> Maybe we should add fixes tag, as it has been broken since the following
> commit:
> Fixes: abec749facff ("fs/proc/page.c: allow inspection of last section
> and fix end detection")

Are you sure that that commit broke it?

I recall that we would naturally run into the limit, because

count = min_t(size_t, count, (max_pfn * KPMSIZE) - src);

wouldn't really do what you would expect either. But you could 
force-read beyond max_pfn, yes, because the count computation was just 
weird.


I think the real issue is not properly adjusting max_pfn in the first 
place when we introduced memoruy hotplug on arm64.

--
Thanks,

David / dhildenb