linux-kernel - Re: [PATCH 2/6] arm64/mm: Enable memory hot remove

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Message-ID: <e191ddcb-271c-57f3-091f-eacaac2e86e0@arm.com>
Date:   Wed, 3 Apr 2019 14:15:01 +0100
From:   Steven Price <steven.price@....com>
To:     Robin Murphy <robin.murphy@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org, will.deacon@....com,
        catalin.marinas@....com
Cc:     mark.rutland@....com, mhocko@...e.com, david@...hat.com,
        logang@...tatee.com, cai@....pw, pasha.tatashin@...cle.com,
        james.morse@....com, cpandya@...eaurora.org, arunks@...eaurora.org,
        dan.j.williams@...el.com, mgorman@...hsingularity.net,
        osalvador@...e.de
Subject: Re: [PATCH 2/6] arm64/mm: Enable memory hot remove

On 03/04/2019 13:37, Robin Murphy wrote:
> [ +Steve ]
> 
> Hi Anshuman,
> 
> On 03/04/2019 05:30, Anshuman Khandual wrote:

<snip>

>> diff --git a/arch/arm64/include/asm/pgtable.h
>> b/arch/arm64/include/asm/pgtable.h
>> index de70c1e..858098e 100644
>> --- a/arch/arm64/include/asm/pgtable.h
>> +++ b/arch/arm64/include/asm/pgtable.h
>> @@ -355,6 +355,18 @@ static inline int pmd_protnone(pmd_t pmd)
>>   }
>>   #endif
>>   +#if (CONFIG_PGTABLE_LEVELS > 2)
>> +#define pmd_large(pmd)    (pmd_val(pmd) && !(pmd_val(pmd) &
>> PMD_TABLE_BIT))
>> +#else
>> +#define pmd_large(pmd) 0
>> +#endif
>> +
>> +#if (CONFIG_PGTABLE_LEVELS > 3)
>> +#define pud_large(pud)    (pud_val(pud) && !(pud_val(pud) &
>> PUD_TABLE_BIT))
>> +#else
>> +#define pud_large(pmd) 0
>> +#endif
> 
> These seem rather different from the versions that Steve is proposing in
> the generic pagewalk series - can you reach an agreement on which
> implementation is preferred?

Indeed this doesn't match the version in my series although is quite
similar.

My desire is that p?d_large represents the hardware architectural
definition of large page/huge page/section (pick your naming). Although
now I look more closely this is actually broken in my series (I'll fix
that up and send a new version shortly) - p?d_sect() is similarly
conditional.

Is there a good reason not to use the existing p?d_sect() macros
available on arm64?

I'm also surprised by the CONFIG_PGTABLE_LEVEL conditions as they don't
match the existing conditions for p?d_sect(). Might be worth double
checking it actually does what you expect.

Steve