linux-kernel - Re: [RFC] arm64: mm: update max

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Date:   Mon, 27 Sep 2021 19:34:02 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Georgi Djakov <quic_c_gdjako@...cinc.com>,
        Chris Goldsworthy <quic_cgoldswo@...cinc.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org,
        Sudarshan Rajagopalan <quic_sudaraja@...cinc.com>
Subject: Re: [RFC] arm64: mm: update max_pfn after memory hotplug

On 27.09.21 19:22, Georgi Djakov wrote:
> On 9/24/2021 1:54 AM, Chris Goldsworthy wrote:
>> From: Sudarshan Rajagopalan <quic_sudaraja@...cinc.com>
>>
>> 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@...cinc.com>
>> Signed-off-by: Chris Goldsworthy <quic_cgoldswo@...cinc.com>
> 
> 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@...cinc.com>
> 
> 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