linux-kernel - Re: [PATCH 06/40] autonuma: x86 pte_numa() and pmd

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Date:	Fri, 29 Jun 2012 11:02:41 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Hillf Danton <dhillf@...il.com>, Dan Smith <danms@...ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Johannes Weiner <hannes@...xchg.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Alex Shi <alex.shi@...el.com>,
	Mauricio Faria de Oliveira <mauricfo@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Don Morris <don.morris@...com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 06/40] autonuma: x86 pte_numa() and pmd_numa()

On 06/28/2012 08:55 AM, Andrea Arcangeli wrote:

>   static inline int pte_file(pte_t pte)
>   {
> -	return pte_flags(pte)&  _PAGE_FILE;
> +	return (pte_flags(pte)&  _PAGE_FILE) == _PAGE_FILE;
>   }

Wait, why is this change made?  Surely _PAGE_FILE is just
one single bit and this change is not useful?

If there is a reason for this change, please document it.

> @@ -405,7 +405,9 @@ static inline int pte_same(pte_t a, pte_t b)
>
>   static inline int pte_present(pte_t a)
>   {
> -	return pte_flags(a)&  (_PAGE_PRESENT | _PAGE_PROTNONE);
> +	/* _PAGE_NUMA includes _PAGE_PROTNONE */
> +	return pte_flags(a)&  (_PAGE_PRESENT | _PAGE_PROTNONE |
> +			       _PAGE_NUMA_PTE);
>   }
>
>   static inline int pte_hidden(pte_t pte)
> @@ -415,7 +417,46 @@ static inline int pte_hidden(pte_t pte)
>
>   static inline int pmd_present(pmd_t pmd)
>   {
> -	return pmd_flags(pmd)&  _PAGE_PRESENT;
> +	return pmd_flags(pmd)&  (_PAGE_PRESENT | _PAGE_PROTNONE |
> +				 _PAGE_NUMA_PMD);
> +}

Somewhat subtle. Better documentation in patch 5 will
help explain this.

> +#ifdef CONFIG_AUTONUMA
> +static inline int pte_numa(pte_t pte)
> +{
> +	return (pte_flags(pte)&
> +		(_PAGE_NUMA_PTE|_PAGE_PRESENT)) == _PAGE_NUMA_PTE;
> +}
> +
> +static inline int pmd_numa(pmd_t pmd)
> +{
> +	return (pmd_flags(pmd)&
> +		(_PAGE_NUMA_PMD|_PAGE_PRESENT)) == _PAGE_NUMA_PMD;
> +}
> +#endif

These could use a little explanation of how _PAGE_NUMA_* is
used and what the flags mean.

> +static inline pte_t pte_mknotnuma(pte_t pte)
> +{
> +	pte = pte_clear_flags(pte, _PAGE_NUMA_PTE);
> +	return pte_set_flags(pte, _PAGE_PRESENT|_PAGE_ACCESSED);
> +}
> +
> +static inline pmd_t pmd_mknotnuma(pmd_t pmd)
> +{
> +	pmd = pmd_clear_flags(pmd, _PAGE_NUMA_PMD);
> +	return pmd_set_flags(pmd, _PAGE_PRESENT|_PAGE_ACCESSED);
> +}
> +
> +static inline pte_t pte_mknuma(pte_t pte)
> +{
> +	pte = pte_set_flags(pte, _PAGE_NUMA_PTE);
> +	return pte_clear_flags(pte, _PAGE_PRESENT);
> +}
> +
> +static inline pmd_t pmd_mknuma(pmd_t pmd)
> +{
> +	pmd = pmd_set_flags(pmd, _PAGE_NUMA_PMD);
> +	return pmd_clear_flags(pmd, _PAGE_PRESENT);
>   }

These functions could use some explanation, too.

Why do the top ones set _PAGE_ACCESSED, while the bottom ones
leave _PAGE_ACCESSED alone?

I can guess the answer, but it should be documented so it is
also clear to people with less experience in the VM.

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