Re: [PATCH 1/2] arm64/mm: Change THP helpers to comply with generic MM semantics

[Ralph Campbell]

On 9/3/20 9:56 AM, Catalin Marinas wrote:
> On Mon, Aug 17, 2020 at 02:49:43PM +0530, Anshuman Khandual wrote:
> > pmd_present() and pmd_trans_huge() are expected to behave in the following
> > manner during various phases of a given PMD. It is derived from a previous
> > detailed discussion on this topic [1] and present THP documentation [2].
> >
> > pmd_present(pmd):
> >
> > - Returns true if pmd refers to system RAM with a valid pmd_page(pmd)
> > - Returns false if pmd does not refer to system RAM - Invalid pmd_page(pmd)
>
> The second bullet doesn't make much sense. If you have a pmd mapping of
> some I/O memory, pmd_present() still returns true (as does
> pte_present()).
>
> > diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
> > index 4d867c6446c4..28792fdd9627 100644
> > --- a/arch/arm64/include/asm/pgtable-prot.h
> > +++ b/arch/arm64/include/asm/pgtable-prot.h
> > @@ -19,6 +19,13 @@
> >   #define PTE_DEVMAP		(_AT(pteval_t, 1) << 57)
> >   #define PTE_PROT_NONE		(_AT(pteval_t, 1) << 58) /* only when !PTE_VALID */
> >   
> > +/*
> > + * This help indicate that the entry is present i.e pmd_page()
>
> Nit: add another . after i.e

Another nit: "This help indicate" => "This helper indicates"

Maybe I should look at the series more. :-)