Re: SLUB: Return ZERO_SIZE_PTR for kmalloc(0)

[Christoph Lameter]

On Fri, 1 Jun 2007, Andrew Morton wrote:

> They are different instances which happen to have the same length (zero).

I guess one could use the slab allocators as a type of reservation 
ticket generator with zero sized objects. Hmmm.... But is that really a 
useful thing to do?

> But the code will incorrectly decide that they are the same instance.  It
> might cause refcounting or accounting errors, for example.  I don't know - the
> kernel's a big place.

That would have to occur with objects that are repeatedly allocated and 
then linked toghether etc. Linking typicallty requires a listhead so its 
typically difficult to do zero length objects.
 
> I agree the risk is low, but if something _does_ blow up, it will do so subtly.

The cases that we have seen so far are due to array allocations of N 
elements where N == 0 leads to the creation of a zero sized object.
The objects of the array are not zero sized it is just that zero of 
them are allocated.
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