[PATCH] MM: use DIV_ROUND_UP() in mm/memory.c

[PATCH] MM: use DIV_ROUND_UP() in mm/memory.c

[Rolf Eike Beer]

This should make no difference in behaviour.

Signed-off-by: Rolf Eike Beer <eike-kernel@sf-tec.de>

---
commit 64aa7c3136258d3abc76354b5f83b9a9575169c0
tree 8037adc04b57cd6150456399b7caccf99489385a
parent bf0bd376f79cadb4f8cd454db1723eb9be0aabc1
author Rolf Eike Beer <eike-kernel@sf-tec.de> Tue, 24 Apr 2007 16:05:40 +0200
committer Rolf Eike Beer <eike-kernel@sf-tec.de> Tue, 24 Apr 2007 16:05:40 
+0200

 mm/memory.c |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index e7066e7..45bba1f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1838,12 +1838,11 @@ void unmap_mapping_range(struct address_space 
*mapping,
 {
 	struct zap_details details;
 	pgoff_t hba = holebegin >> PAGE_SHIFT;
-	pgoff_t hlen = (holelen + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	pgoff_t hlen = DIV_ROUND_UP(holelen, PAGE_SIZE);
 
 	/* Check for overflow. */
 	if (sizeof(holelen) > sizeof(hlen)) {
-		long long holeend =
-			(holebegin + holelen + PAGE_SIZE - 1) >> PAGE_SHIFT;
+		long long holeend = DIV_ROUND_UP(holebegin + holelen, PAGE_SIZE);
 		if (holeend & ~(long long)ULONG_MAX)
 			hlen = ULONG_MAX - hba + 1;
 	}
@@ -2592,7 +2591,7 @@ int make_pages_present(unsigned long addr, unsigned long 
end)
 	write = (vma->vm_flags & VM_WRITE) != 0;
 	BUG_ON(addr >= end);
 	BUG_ON(end > vma->vm_end);
-	len = (end+PAGE_SIZE-1)/PAGE_SIZE-addr/PAGE_SIZE;
+	len = DIV_ROUND_UP(end, PAGE_SIZE) - addr/PAGE_SIZE;
 	ret = get_user_pages(current, current->mm, addr,
 			len, write, 0, NULL, NULL);
 	if (ret < 0)

Re: [PATCH] MM: use DIV_ROUND_UP() in mm/memory.c

[Andrew Morton]

On Tue, 24 Apr 2007 16:10:22 +0200 Rolf Eike Beer <eike-kernel@sf-tec.de> wrote:

> This should make no difference in behaviour.
> 
> Signed-off-by: Rolf Eike Beer <eike-kernel@sf-tec.de>
> 
> ---
> commit 64aa7c3136258d3abc76354b5f83b9a9575169c0
> tree 8037adc04b57cd6150456399b7caccf99489385a
> parent bf0bd376f79cadb4f8cd454db1723eb9be0aabc1
> author Rolf Eike Beer <eike-kernel@sf-tec.de> Tue, 24 Apr 2007 16:05:40 +0200
> committer Rolf Eike Beer <eike-kernel@sf-tec.de> Tue, 24 Apr 2007 16:05:40 
> +0200
> 
>  mm/memory.c |    7 +++----
>  1 files changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index e7066e7..45bba1f 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1838,12 +1838,11 @@ void unmap_mapping_range(struct address_space 
> *mapping,
>  {
>  	struct zap_details details;
>  	pgoff_t hba = holebegin >> PAGE_SHIFT;
> -	pgoff_t hlen = (holelen + PAGE_SIZE - 1) >> PAGE_SHIFT;
> +	pgoff_t hlen = DIV_ROUND_UP(holelen, PAGE_SIZE);
>  
>  	/* Check for overflow. */
>  	if (sizeof(holelen) > sizeof(hlen)) {
> -		long long holeend =
> -			(holebegin + holelen + PAGE_SIZE - 1) >> PAGE_SHIFT;
> +		long long holeend = DIV_ROUND_UP(holebegin + holelen, PAGE_SIZE);
>  		if (holeend & ~(long long)ULONG_MAX)
>  			hlen = ULONG_MAX - hba + 1;
>  	}
> @@ -2592,7 +2591,7 @@ int make_pages_present(unsigned long addr, unsigned long 
> end)
>  	write = (vma->vm_flags & VM_WRITE) != 0;
>  	BUG_ON(addr >= end);
>  	BUG_ON(end > vma->vm_end);
> -	len = (end+PAGE_SIZE-1)/PAGE_SIZE-addr/PAGE_SIZE;
> +	len = DIV_ROUND_UP(end, PAGE_SIZE) - addr/PAGE_SIZE;
>  	ret = get_user_pages(current, current->mm, addr,
>  			len, write, 0, NULL, NULL);
>  	if (ret < 0)

The patch is wordwrapped.  Please fix your MUA.

More seriously, on i386:

   text    data     bss     dec     hex filename
  15509      27      28   15564    3ccc mm/memory.o	(before)
  15561      27      28   15616    3d00 mm/memory.o	(after)

I'm not sure why - some of the quantities which we're dividing by there are
64-bit and perhaps the compiler has decided not to do shifting.

Please always check the before-and-after .text size from now on?

Now I'm worried about all the other DIV_ROUND_UP() conversions we did.  We
should get in there and work out why it went bad.

[PATCH] MM: use DIV_ROUND_UP() in mm/memory.c

[Rolf Eike Beer]

Replace a hand coded version of DIV_ROUND_UP().

Signed-off-by: Rolf Eike Beer <eike-kernel@sf-tec.de

---
commit ab35916f807eb4f2019a208e96cb0bddbb91dfc3
tree 6dc4485902c1a96a09ed287270de108630b26719
parent 335aa0289219ca2c1dc309d6bf856d4b25ad8746
author Rolf Eike Beer <eike-kernel@sf-tec.de> Thu, 17 May 2007 23:03:06 +0200
committer Rolf Eike Beer <eike-kernel@sf-tec.de> Thu, 17 May 2007 23:03:06 +0200

 mm/memory.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index cb94488..5bc26b7 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2674,7 +2674,7 @@ int make_pages_present(unsigned long addr, unsigned long end)
 	write = (vma->vm_flags & VM_WRITE) != 0;
 	BUG_ON(addr >= end);
 	BUG_ON(end > vma->vm_end);
-	len = (end+PAGE_SIZE-1)/PAGE_SIZE-addr/PAGE_SIZE;
+	len = DIV_ROUND_UP(end, PAGE_SIZE) - addr/PAGE_SIZE;
 	ret = get_user_pages(current, current->mm, addr,
 			len, write, 0, NULL, NULL);
 	if (ret < 0)

Re: [PATCH] MM: use DIV_ROUND_UP() in mm/memory.c

[Rolf Eike Beer]

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Andrew Morton wrote:
> Rolf Eike Beer wrote:

>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -1838,12 +1838,11 @@ void unmap_mapping_range(struct address_space
>> *mapping,
>>  {
>>  	struct zap_details details;
>>  	pgoff_t hba = holebegin >> PAGE_SHIFT;
>> -	pgoff_t hlen = (holelen + PAGE_SIZE - 1) >> PAGE_SHIFT;
>> +	pgoff_t hlen = DIV_ROUND_UP(holelen, PAGE_SIZE);
>>
>>  	/* Check for overflow. */
>>  	if (sizeof(holelen) > sizeof(hlen)) {
>> -		long long holeend =
>> -			(holebegin + holelen + PAGE_SIZE - 1) >> PAGE_SHIFT;
>> +		long long holeend = DIV_ROUND_UP(holebegin + holelen, PAGE_SIZE);
>>  		if (holeend & ~(long long)ULONG_MAX)
>>  			hlen = ULONG_MAX - hba + 1;
>>  	}
>> @@ -2592,7 +2591,7 @@ int make_pages_present(unsigned long addr, unsigned
>> long end)
>>  	write = (vma->vm_flags & VM_WRITE) != 0;
>>  	BUG_ON(addr >= end);
>>  	BUG_ON(end > vma->vm_end);
>> -	len = (end+PAGE_SIZE-1)/PAGE_SIZE-addr/PAGE_SIZE;
>> +	len = DIV_ROUND_UP(end, PAGE_SIZE) - addr/PAGE_SIZE;
>>  	ret = get_user_pages(current, current->mm, addr,
>>  			len, write, 0, NULL, NULL);
>>  	if (ret < 0)
>
> More seriously, on i386:
>
>    text    data     bss     dec     hex filename
>   15509      27      28   15564    3ccc mm/memory.o	(before)
>   15561      27      28   15616    3d00 mm/memory.o	(after)
>
> I'm not sure why - some of the quantities which we're dividing by there are
> 64-bit and perhaps the compiler has decided not to do shifting.
>
> Now I'm worried about all the other DIV_ROUND_UP() conversions we did.  We
> should get in there and work out why it went bad.

It's the first two places that cause the increase in code size. The last one 
is the exact replacement of how DIV_ROUND_UP() is defined so that can hardly 
make a difference.

If the compiler can't find out to do shifting we might want to improve 
DIV_ROUND_UP() to do some tricks with __builtin_constant_p() to do the shift. 
Something like:

#define DIV_ROUND_UP(n, d)			\
(						\
	__builtin_constant_p(d) ? (		\
		is_power_of_2(d) ?		\
		(((n) + (d) - 1) >> ilog2(d)) :	\
		(((n) + (d) - 1) / (d))		\
	) :					\
	(((n) + (d) - 1) / (d))			\
)

With this version mm/memory.o will result in the same size with and without my 
patch so I guess it's doing what it should. If you like it tell me and I'll 
send a patch.

Eike

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