Re: Reducing the chunk header sizes on all memory context types

I wrote:
> So the bug is in fact in David's changes, and it consists in palloc
> sometimes handing back non-maxaligned pointers.  I find it mildly
> astonishing that we managed to get through core regression tests
> without such a fault surfacing, but there you have it.

Oh!  I just noticed that the troublesome context (rb->change_context)
is a SlabContext, so it may be that this only happens in non-aset
contexts.  It's a lot easier to believe that the core tests never
exercise the case of pfree'ing a slab chunk.

            regards, tom lane