linux-kernel - Re: [KJ] [PATCH] is_power_of

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Date:	Fri, 16 Feb 2007 18:36:57 +0100
From:	Richard Knutsson <ricknu-0@...dent.ltu.se>
To:	"Robert P. J. Day" <rpjday@...dspring.com>
CC:	Andreas Schwab <schwab@...e.de>, linux-mm@...ck.org,
	tony.luck@...el.com, linux-ia64@...r.kernel.org,
	Kernel Janitors List <kernel-janitors@...ts.osdl.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [KJ] [PATCH] is_power_of_2 in ia64mm

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-0@...dent.ltu.se> writes:
>>>
>>>       
>>>> Andreas Schwab wrote:
>>>>
>>>>         
>>>>> Richard Knutsson <ricknu-0@...dent.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 specified\n");
>>>>>>>
>>>>>>>               
>>>>>> 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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