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

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Date:	Thu, 5 Jul 2012 01:03:50 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Rik van Riel <riel@...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 Fri, Jun 29, 2012 at 11:02:41AM -0400, Rik van Riel wrote:
> 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.

I splitted it off to a separated patch with proper commit log here.

http://git.kernel.org/?p=linux/kernel/git/andrea/aa.git;a=commitdiff;h=7b2292c7ab86205f3d630533dc9987449fea6347

I haven't checked if it spawns the same warning without the patchset
applied, but I need the build not to show warnings, so while it may be
irrelevant warning for upstream, I don't like to have warnings.

> >   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.

It's as subtle as PROTNONE but I added more explanation below as well
as in patch 5.

> > +#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.

Added:

http://git.kernel.org/?p=linux/kernel/git/andrea/aa.git;a=commitdiff;h=0e6537227de32c40bbf0a5bc6b11d27ba5779e68

> > +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.

Added too in prev link.
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