Re: [KJ] [PATCH] is_power_of_2 in ia64mm

[Richard Knutsson <ricknu-0@student.ltu.se>]

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@student.ltu.se> writes:
> > >
> > >       
> > > > Andreas Schwab wrote:
> > > >
> > > >         
> > > > > Richard Knutsson <ricknu-0@student.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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