is_power_of_2 in ia64mm

Replacing (n & (n-1)) in the context of power of 2
checks
with is_power_of_2


diff --git a/arch/ia64/mm/hugetlbpage.c
b/arch/ia64/mm/hugetlbpage.c
index 0c7e94e..0ccc70e 100644
--- a/arch/ia64/mm/hugetlbpage.c
+++ b/arch/ia64/mm/hugetlbpage.c
 -16,6
+16,7 
 #include <linux/smp_lock.h>
 #include <linux/slab.h>
 #include <linux/sysctl.h>
+#include <linux/log2.h>
 #include <asm/mman.h>
 #include <asm/pgalloc.h>
 #include <asm/tlb.h>
 -175,7
+176,7  static int __init hugetlb_setup_sz(char *str)
 		tr_pages = 0x15557000UL;
 
 	size = memparse(str, &str);
-	if (*str || (size & (size-1)) || !(tr_pages &
size) ||
+	if (*str || !is_power_of_2(size) || !(tr_pages & size)
||
 		size <= PAGE_SIZE ||
 		size >= (1UL << PAGE_SHIFT << MAX_ORDER))
{
 		printk(KERN_WARNING "Invalid huge page size
specifiedn");

-- 
Regards,  
Vignesh Babu BM  
____________________________________________________________
_  
"Why is it that every time I'm with you, makes me
believe in magic?"
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Vignesh Babu BM wrote:
> Replacing (n & (n-1)) in the context of power of 2
checks
> with is_power_of_2
>
>
> diff --git a/arch/ia64/mm/hugetlbpage.c
b/arch/ia64/mm/hugetlbpage.c
> index 0c7e94e..0ccc70e 100644
> --- a/arch/ia64/mm/hugetlbpage.c
> +++ b/arch/ia64/mm/hugetlbpage.c
>  -16,6 +16,7 
>  #include <linux/smp_lock.h>
>  #include <linux/slab.h>
>  #include <linux/sysctl.h>
> +#include <linux/log2.h>
>  #include <asm/mman.h>
>  #include <asm/pgalloc.h>
>  #include <asm/tlb.h>
>  -175,7 +176,7  static int __init hugetlb_setup_sz(char
*str)
>  		tr_pages = 0x15557000UL;
>  
>  	size = memparse(str, &str);
> -	if (*str || (size & (size-1)) || !(tr_pages &
size) ||
> +	if (*str || !is_power_of_2(size) || !(tr_pages &
size) ||
>  		size <= PAGE_SIZE ||
>  		size >= (1UL << PAGE_SHIFT <<
MAX_ORDER)) {
>  		printk(KERN_WARNING "Invalid huge page size
specifiedn");
>
>   
As we talked about before; is this really correct?
!is_power_of_2(0) == 
true while (0 & (0-1)) == 0.

Richard Knutsson

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Richard Knutsson <ricknu-0student.ltu.se> writes:

> Vignesh Babu BM wrote:
>>  -175,7 +176,7  static int __init hugetlb_setup_sz(char
*str)
>>  		tr_pages = 0x15557000UL;
>>   	size = memparse(str, &str);
>> -	if (*str || (size & (size-1)) || !(tr_pages
& size) ||
>> +	if (*str || !is_power_of_2(size) || !(tr_pages
& size) ||
>>  		size <= PAGE_SIZE ||
>>  		size >= (1UL << PAGE_SHIFT <<
MAX_ORDER)) {
>>  		printk(KERN_WARNING "Invalid huge page size
specifiedn");
>>
>>   
> As we talked about before; is this really correct?
!is_power_of_2(0) ==
> true while (0 & (0-1)) == 0.

size == 0 is also covered by the next two conditions, so the
overall value
does not change.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwabsuse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg,
Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5
214B 8276 4ED5
"And now for something completely different."
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Richard Knutsson <ricknu-0student.ltu.se> writes:

> Andreas Schwab wrote:
>> Richard Knutsson <ricknu-0student.ltu.se> writes:
>>
>>   
>>> Vignesh Babu BM wrote:
>>>     
>>>>  -175,7 +176,7  static int __init
hugetlb_setup_sz(char *str)
>>>>  		tr_pages = 0x15557000UL;
>>>>   	size = memparse(str, &str);
>>>> -	if (*str || (size & (size-1)) ||
!(tr_pages & size) ||
>>>> +	if (*str || !is_power_of_2(size) ||
!(tr_pages & size) ||
>>>>  		size <= PAGE_SIZE ||
>>>>  		size >= (1UL << PAGE_SHIFT
<< MAX_ORDER)) {
>>>>  		printk(KERN_WARNING "Invalid huge
page size specifiedn");
>>>>
>>>>         
>>> As we talked about before; is this really
correct? !is_power_of_2(0) ==
>>> true while (0 & (0-1)) == 0.
>>>     
>>
>> size == 0 is also covered by the next two
conditions, so the overall value
>> does not change.
>>   
> Yes, but is it meant to state that 'size' is not a
power of two?

What else can it mean?

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwabsuse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg,
Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5
214B 8276 4ED5
"And now for something completely different."
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Richard Knutsson <ricknu-0student.ltu.se> writes:

> Andreas Schwab wrote:
>> Richard Knutsson <ricknu-0student.ltu.se> writes:
>>   
>>> Andreas Schwab wrote:
>>>     
>>>> Richard Knutsson <ricknu-0student.ltu.se> writes:
>>>>         
>>>>> Vignesh Babu BM wrote:
>>>>>         
>>>>>>  -175,7 +176,7  static
int __init hugetlb_setup_sz(char *str)
>>>>>>  		tr_pages = 0x15557000UL;
>>>>>>   	size = memparse(str, &str);
>>>>>> -	if (*str || (size & (size-1))
|| !(tr_pages & size) ||
>>>>>> +	if (*str || !is_power_of_2(size)
|| !(tr_pages & size) ||
>>>>>>  		size <= PAGE_SIZE ||
>>>>>>  		size >= (1UL <<
PAGE_SHIFT << MAX_ORDER)) {
>>>>>>  		printk(KERN_WARNING
"Invalid huge page size specifiedn");
>>>>>>           
>>>>> As we talked about before; is this
really correct? !is_power_of_2(0) ==
>>>>> true while (0 & (0-1)) == 0.
>>>>>         
>>>> size == 0 is also covered by the next two
conditions, so the overall value
>>>> does not change.
>>>>       
>>> Yes, but is it meant to state that 'size' is
not a power of two?
>>>     
>>
>> What else can it mean?
>>   
> What about !one_or_less_bit()?

Obviously not.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwabsuse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg,
Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5
214B 8276 4ED5
"And now for something completely different."
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On Fri, 16 Feb 2007, Richard Knutsson wrote:

> Andreas Schwab wrote:
> > Richard Knutsson <ricknu-0student.ltu.se> writes:
> >
> >
> > > Vignesh Babu BM wrote:
> > >
> > > >  -175,7 +176,7  static int __init
hugetlb_setup_sz(char *str)
> > > >  		tr_pages = 0x15557000UL;
> > > >   	size = memparse(str, &str);
> > > > -	if (*str || (size & (size-1)) ||
!(tr_pages & size) ||
> > > > +	if (*str || !is_power_of_2(size) ||
!(tr_pages & size) ||
> > > >  		size <= PAGE_SIZE ||
> > > >  		size >= (1UL << PAGE_SHIFT
<< MAX_ORDER)) {
> > > >  		printk(KERN_WARNING "Invalid
huge page size specifiedn");
> > > >
> > > >
> > > As we talked about before; is this really
correct?
> > > !is_power_of_2(0) == true while (0 &
(0-1)) == 0.
> >
> > size == 0 is also covered by the next two
conditions, so the
> > overall value does not change.
> >
> Yes, but is it meant to state that 'size' is not a
power of two?
> Otherwise, imho, it should be left as-is.

i think the above change is fine.  as long as the final,
overall
semantics of the condition are identical, then there's no
problem.

rday

-- 
============================================================
============
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry
Waterloo, Ontario, CANADA

http:
//fsdev.net/wiki/index.php?title=Main_Page
============================================================
============
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i'm not clear on what the possible problem is here:

On Fri, 16 Feb 2007, Richard Knutsson wrote:

> Andreas Schwab wrote:
> > Richard Knutsson <ricknu-0student.ltu.se> writes:
> >
> >> Andreas Schwab wrote:
> >>
> >>> Richard Knutsson <ricknu-0student.ltu.se> writes:
> >>>
> >>>
> >>>> Vignesh Babu BM wrote:
> >>>>
> >>>>>  -175,7 +176,7  static
int __init hugetlb_setup_sz(char *str)
> >>>>>  		tr_pages = 0x15557000UL;
> >>>>>   	size = memparse(str,
&str);
> >>>>> -	if (*str || (size &
(size-1)) || !(tr_pages & size) ||
> >>>>> +	if (*str || !is_power_of_2(size)
|| !(tr_pages & size) ||
> >>>>>  		size <= PAGE_SIZE ||
> >>>>>  		size >= (1UL <<
PAGE_SHIFT << MAX_ORDER)) {
> >>>>>  		printk(KERN_WARNING
"Invalid huge page size specifiedn");
> >>>>>
> >>>> As we talked about before; is this
really correct? !is_power_of_2(0) ==
> >>>> true while (0 & (0-1)) == 0.
> >>>>
> >>> size == 0 is also covered by the next two
conditions, so the overall value
> >>> does not change.
> >>>
> >> Yes, but is it meant to state that 'size' is
not a power of two?
> >>
> >
> > What else can it mean?

> What about !one_or_less_bit()? It has not been
implemented (yet?)
> but been discussed.

but whether or not it's been implemented doesn't change
whether or not
the code above can be simplified.  given what's being
tested, and the
error message about whether a page size is valid, it seems
fairly
clear that this is a power of two test.  what's the
problem?

> It ended by concluding that is_power_of_2() should be
fixed up first
> and then we can see about it.

there's nothing about is_power_of_2() that needs
"fixing".  it's
correct as it's currently implemented.

> And as I stated before; !is_power_of_2(size) != (size
& (size-1))!
> It may be a bug but then we have to be sure it is
suppose to be the
> power of 2.

it may be that certain tests in the current code need to be
examined
carefully to clarify what's being tested.  but the code
above seems
straightforward.

rday

-- 
============================================================
============
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry
Waterloo, Ontario, CANADA

http:
//fsdev.net/wiki/index.php?title=Main_Page
============================================================
============
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Robert P. J. Day wrote:
> i'm not clear on what the possible problem is here:
>
> On Fri, 16 Feb 2007, Richard Knutsson wrote:
>
>   
>> Andreas Schwab wrote:
>>     
>>> Richard Knutsson <ricknu-0student.ltu.se> writes:
>>>
>>>       
>>>> Andreas Schwab wrote:
>>>>
>>>>         
>>>>> Richard Knutsson <ricknu-0student.ltu.se> writes:
>>>>>
>>>>>
>>>>>           
>>>>>> Vignesh Babu BM wrote:
>>>>>>
>>>>>>             
>>>>>>>  -175,7 +176,7  static
int __init hugetlb_setup_sz(char *str)
>>>>>>>  		tr_pages = 0x15557000UL;
>>>>>>>   	size = memparse(str,
&str);
>>>>>>> -	if (*str || (size &
(size-1)) || !(tr_pages & size) ||
>>>>>>> +	if (*str ||
!is_power_of_2(size) || !(tr_pages & size) ||
>>>>>>>  		size <= PAGE_SIZE ||
>>>>>>>  		size >= (1UL <<
PAGE_SHIFT << MAX_ORDER)) {
>>>>>>>  		printk(KERN_WARNING
"Invalid huge page size specifiedn");
>>>>>>>
>>>>>>>               
>>>>>> As we talked about before; is this
really correct? !is_power_of_2(0) ==
>>>>>> true while (0 & (0-1)) == 0.
>>>>>>
>>>>>>             
>>>>> size == 0 is also covered by the next
two conditions, so the overall value
>>>>> does not change.
>>>>>
>>>>>           
>>>> Yes, but is it meant to state that 'size'
is not a power of two?
>>>>
>>>>         
>>> What else can it mean?
>>>       
>> What about !one_or_less_bit()? It has not been
implemented (yet?)
>> but been discussed.
>>     
>
> but whether or not it's been implemented doesn't change
whether or not
> the code above can be simplified.  given what's being
tested, and the
> error message about whether a page size is valid, it
seems fairly
> clear that this is a power of two test.  what's the
problem?
>   
Fsck, I can't see that. But if that is what's intended, well
then...

(5 min later)
Ok, now I think I see it. Sorry for the noise..
>   
>> It ended by concluding that is_power_of_2() should
be fixed up first
>> and then we can see about it.
>>     
>
> there's nothing about is_power_of_2() that needs
"fixing".  it's
> correct as it's currently implemented.
>   
Oh, I didn't mean that is_power_of_2() need to be fixed, I
meant 
fixing/replacing the kernel with is_power_of_2().


Todays lesson: don't try to code while you have a cold...
Richard Knutsson

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