linux-kernel - Re: [PATCH] x86/mm: Make pud_present() check _PAGE_PROTNONE and _PAGE

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Date:   Fri, 20 Mar 2020 12:50:03 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        "Kirill A. Shutemov" <kirill@...temov.name>
CC:     <linux-mm@...ck.org>, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH] x86/mm: Make pud_present() check _PAGE_PROTNONE and
 _PAGE_PSE as well

On 3/20/20 6:22 AM, Anshuman Khandual wrote:
...
>>> +Cc: Kirill A. Shutemov <kirill@...temov.name>
>>> +Cc: Dan Williams <dan.j.williams@...el.com>
>>
>> Or we can just drop the pud_mknotpresent(). There's no users AFAICS and
>> only x86 provides it.

+1

> 
> Yes that will be an option but IMHO fixing pud_present() here might be
> a better choice because,
> 
> (1) pud_mknotpresent() with fixed pud_present() might be required later


It might. Or it might not. Let's wait until it's actually used, and see.
Dead code is an avoidable expense (adds size, space on the screen, email
traffic and other wasted time), so let's avoid it here.


> (2) PMD & PUD will be exact same (THP is supported on either level)
> 
> Nonetheless, I am happy to go either way.
> 


thanks,
-- 
John Hubbard
NVIDIA