linux-kernel - Re: [PATCH -mm] PAGE_ALIGN(): correctly handle 64-bit values on 32-bit architectures (v2)

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Message-ID: <485625D9.6040508@gmail.com>
Date:	Mon, 16 Jun 2008 10:35:37 +0200 (MEST)
From:	Andrea Righi <righi.andrea@...il.com>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	balbir@...ux.vnet.ibm.com,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	yamamoto@...inux.co.jp, menage@...gle.com,
	linux-kernel@...r.kernel.org, xemul@...nvz.org,
	kamezawa.hiroyu@...fujitsu.com, linux-arch@...r.kernel.org
Subject: Re: [PATCH -mm] PAGE_ALIGN(): correctly handle 64-bit values on 32-bit
 architectures (v2)

Paul Mackerras wrote:
> Andrea Righi writes:
> 
>> Also move the PAGE_ALIGN() definitions out of include/asm-*/page.h in
>> include/linux/mm.h.
> 
> I'd rather see it in some other place than this, because
> include/linux/mm.h is a large header that includes quite a lot of
> other stuff.  What's wrong with leaving it in each arch's page.h and
> only changing it on those archs that have both 32-bit and 64-bit
> variants?  Or perhaps there is some other, lower-level header in
> include/linux where it could go?

I think the only evident advantage of this is to have a single
implementation, instead of dealing with (potentially) N different
implementations.

Maybe a different place could be linux/mm_types.h, it's not so small,
but at least it's smaller than linux/mm.h. However, it's a bit ugly to
put a "function" in a file called mm_types.h.

Anyway, I've to say that fixing PAGE_ALIGN and leaving it in each page.h
for now would be surely a simpler solution and would introduce less
potential errors.

> 
>> diff --git a/arch/powerpc/boot/of.c b/arch/powerpc/boot/of.c
>> index 61d9899..6bc72b1 100644
>> --- a/arch/powerpc/boot/of.c
>> +++ b/arch/powerpc/boot/of.c
>> @@ -8,6 +8,7 @@
>>   */
>>  #include <stdarg.h>
>>  #include <stddef.h>
>> +#include <linux/mm.h>
>>  #include "types.h"
>>  #include "elf.h"
>>  #include "string.h"
>> diff --git a/arch/powerpc/boot/page.h b/arch/powerpc/boot/page.h
>> index 14eca30..aa42298 100644
>> --- a/arch/powerpc/boot/page.h
>> +++ b/arch/powerpc/boot/page.h
>> @@ -28,7 +28,4 @@
>>  /* align addr on a size boundary - adjust address up if needed */
>>  #define _ALIGN(addr,size)     _ALIGN_UP(addr,size)
>>  
>> -/* to align the pointer to the (next) page boundary */
>> -#define PAGE_ALIGN(addr)	_ALIGN(addr, PAGE_SIZE)
>> -
>>  #endif				/* _PPC_BOOT_PAGE_H */
> 
> These parts are NAKed, because arch/powerpc/boot is a separate program
> that doesn't use the kernel include files.

OK, so we also shouldn't use the linux/kernel.h's ALIGN() here, but leave
the local _ALIGN() definition, right?

> 
>> diff --git a/include/asm-powerpc/page.h b/include/asm-powerpc/page.h
>> index cffdf0e..e088545 100644
>> --- a/include/asm-powerpc/page.h
>> +++ b/include/asm-powerpc/page.h
>> @@ -119,9 +119,6 @@ extern phys_addr_t kernstart_addr;
>>  /* align addr on a size boundary - adjust address up if needed */
>>  #define _ALIGN(addr,size)     _ALIGN_UP(addr,size)
>>  
>> -/* to align the pointer to the (next) page boundary */
>> -#define PAGE_ALIGN(addr)	_ALIGN(addr, PAGE_SIZE)
>> -
>>  /*
>>   * Don't compare things with KERNELBASE or PAGE_OFFSET to test for
>>   * "kernelness", use is_kernel_addr() - it should do what you want.
> 
> We had already come across this issue on powerpc, and we fixed it by
> making sure that the type of PAGE_MASK was int, not unsigned int.
> However, I have no objection to using the ALIGN() macro from
> include/linux/kernel.h instead.

Thanks,
-Andrea
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