Re: [KJ] [PATCH] is_power_of_2 in ia64mm

From: Richard Knutsson
Date: Fri Feb 16 2007 - 12:37:34 EST

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@xxxxxxxxxxxxxx> writes:

Andreas Schwab wrote:

Richard Knutsson <ricknu-0@xxxxxxxxxxxxxx> 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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