linux-kernel - [PATCH] Cast __page_to_pfn to unsigned long in CONFIG

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Date:	Mon, 19 Nov 2007 14:52:58 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Dave Hansen <haveblue@...ibm.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, mbligh@...gle.com
Subject: [PATCH] Cast __page_to_pfn to unsigned long in CONFIG_SPARSEMEM

* Dave Hansen (haveblue@...ibm.com) wrote:
> On Mon, 2007-11-19 at 13:52 -0500, Mathieu Desnoyers wrote:
> > > > So I guess the result is a pointer ? Should this be expected ?
> > > 
> > > Nope.  'pointer - pointer' is an integer.  Just solve this equation for
> > > integer:
> > > 
> > >       'pointer + integer = pointer'
> > > 
> > 
> > Well, using page_to_pfn turns out to be ugly in markers (and in
> > printks) then. Depending on the architecture, it will result in either
> > an unsigned long (x86_64) or an unsigned int (i386), which corresponds
> > to %lu or %u and will print a warning if we don't cast it explicitly. 
> 
> Casting the i386 one to be an unconditional 'unsigned long' shouldn't be
> an issue.  We don't generally expect pfns to fit into ints anyway. 

So would this make sense ?

Cast __page_to_pfn to unsigned long in CONFIG_SPARSEMEM

Make sure the type returned by __page_to_pfn is always unsigned long. If we
don't cast it explicitly, it can be int on i386, but long on x86_64. This is
especially inelegant for printks.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC: Dave Hansen <haveblue@...ibm.com>
CC: linux-mm@...ck.org
CC: linux-kernel@...r.kernel.org
---
 include/asm-generic/memory_model.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6-lttng/include/asm-generic/memory_model.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-generic/memory_model.h	2007-11-19 14:47:30.000000000 -0500
+++ linux-2.6-lttng/include/asm-generic/memory_model.h	2007-11-19 14:48:30.000000000 -0500
@@ -50,7 +50,7 @@
 
 /* memmap is virtually contigious.  */
 #define __pfn_to_page(pfn)	(vmemmap + (pfn))
-#define __page_to_pfn(page)	((page) - vmemmap)
+#define __page_to_pfn(page)	((unsigned long)((page) - vmemmap))
 
 #elif defined(CONFIG_SPARSEMEM)
 /*

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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