linux-kernel - Re: [PATCH 02/10] mm: Add p[te|md] protnone helpers for use by NUMA balancing

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Message-ID: <20141202101210.GA6043@suse.de>
Date:	Tue, 2 Dec 2014 10:12:10 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>,
	LinuxPPC-dev <linuxppc-dev@...ts.ozlabs.org>,
	Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
	Hugh Dickins <hughd@...gle.com>, Dave Jones <davej@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Paul Mackerras <paulus@...ba.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 02/10] mm: Add p[te|md] protnone helpers for use by NUMA
 balancing

On Tue, Dec 02, 2014 at 09:38:39AM +1100, Benjamin Herrenschmidt wrote:
> On Fri, 2014-11-21 at 13:57 +0000, Mel Gorman wrote:
> 
> >  #ifdef CONFIG_NUMA_BALANCING
> > +/*
> > + * These work without NUMA balancing but the kernel does not care. See the
> > + * comment in include/asm-generic/pgtable.h
> > + */
> > +static inline int pte_protnone(pte_t pte)
> > +{
> > +	return (pte_val(pte) &
> > +		(_PAGE_PRESENT | _PAGE_USER)) == _PAGE_PRESENT;
> > +}
> 
> I would add a comment clarifying that this only works for user pages,
> ie, this accessor will always return "true" for a kernel page on ppc.
> 

diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
index 490bd6d..7b889a3 100644
--- a/arch/powerpc/include/asm/pgtable.h
+++ b/arch/powerpc/include/asm/pgtable.h
@@ -41,7 +41,8 @@ static inline pgprot_t pte_pgprot(pte_t pte)	{ return __pgprot(pte_val(pte) & PA
 #ifdef CONFIG_NUMA_BALANCING
 /*
  * These work without NUMA balancing but the kernel does not care. See the
- * comment in include/asm-generic/pgtable.h
+ * comment in include/asm-generic/pgtable.h . On powerpc, this will only
+ * work for user pages and always return true for kernel pages.
  */
 static inline int pte_protnone(pte_t pte)
 {

-- 
Mel Gorman
SUSE Labs
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