linux-kernel - Re: [PATCH 1/1] mm/hugetlb: Make huge_pte_offset() consistent and document behaviour

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Date:   Wed, 26 Jul 2017 09:39:46 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Punit Agrawal <punit.agrawal@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, steve.capper@....com,
        will.deacon@....com, kirill.shutemov@...ux.intel.com,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: Re: [PATCH 1/1] mm/hugetlb: Make huge_pte_offset() consistent and
 document behaviour

On Tue, Jul 25, 2017 at 04:41:14PM +0100, Punit Agrawal wrote:
> When walking the page tables to resolve an address that points to
> !p*d_present() entry, huge_pte_offset() returns inconsistent values
> depending on the level of page table (PUD or PMD).
> 
> It returns NULL in the case of a PUD entry while in the case of a PMD
> entry, it returns a pointer to the page table entry.
> 
> A similar inconsitency exists when handling swap entries - returns NULL
> for a PUD entry while a pointer to the pte_t is retured for the PMD
> entry.
> 
> Update huge_pte_offset() to make the behaviour consistent - return NULL
> in the case of p*d_none() and a pointer to the pte_t for hugepage or
> swap entries.
> 
> Document the behaviour to clarify the expected behaviour of this
> function. This is to set clear semantics for architecture specific
> implementations of huge_pte_offset().
> 
> Signed-off-by: Punit Agrawal <punit.agrawal@....com>

Reviewed-by: Catalin Marinas <catalin.marinas@....com>