Re: Reducing the chunk header sizes on all memory context types - Mailing list pgsql-hackers

Tomas Vondra <tomas.vondra@enterprisedb.com> writes:
> I suspect it's a pre-existing bug in Slab allocator, because it does this:

> #define SlabBlockGetChunk(slab, block, idx) \
>     ((MemoryChunk *) ((char *) (block) + sizeof(SlabBlock)    \
>                     + (idx * slab->fullChunkSize)))

> and SlabBlock is only 20B, i.e. not a multiple of 8B. Which would mean
> that even if we allocate block and size the chunks carefully (with all
> the MAXALIGN things), we ultimately slice the block incorrectly.

Right, same conclusion I just came to.  But it's not a "pre-existing"
bug, because sizeof(SlabBlock) *was* maxaligned until David added
another field to it.

I think adding a padding field to SlabBlock would be a less messy
solution than your patch.

            regards, tom lane