Re: slab redzoning

[Manfred Spraul <manfred@colorfullife.com>]

William Lee Irwin III wrote:

>On Sat, May 22, 2004 at 10:02:25AM +0200, Manfred Spraul wrote:
>  
>
>>Why this change? I've tested my fls(size-1)==fls(size-1-3*4) approach 
>>and it always returned the right result: No redzoning between 8181 and 
>>8192 bytes, between 16373 and 16384, etc.
>>    
>>
>
>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.
>
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.

--
    Manfred