William Lee Irwin III wrote:

>William Lee Irwin III wrote:
>  
>
>>>It returns a false positive when size + 3*BYTES_PER_WORD == 2**n, e.g.
>>>size == 16373. Here, fls(size - 1) == 13, but fls(size - 1 + 12) == 13
>>>while size - 1 + 12 == 16384, where we'd want the check to fail.
>>>      
>>>
>
>On Sat, May 22, 2004 at 10:43:47AM +0200, Manfred Spraul wrote:
>  
>
>>No, 16373 must fail: After adding 12 bytes the object size would be 
>>16385, which would mean an order==3 allocation.
>>And 16372 must succeed: 16384 is still an order==2 allocation.
>>The idea is that there shouldn't be an allocation order increase due to 
>>redzoning, and afaics that doesn't happen, except between 4082 and 4095 
>>bytes.
>>    
>>
>
>Yes. While you've corrected the one-offs in my post (arithmetic is boring,
>we have machines to do that for us now)
>
I admit, I'm cheating:
I'd copied the test to user space and then tested all values between 32 
and 131072. 16372 passes:
fls(16371) == fls(16383).

I'll send a patch to Andrew to fix the range between 4084 and 4095.

--
    Manfred