Re: pgsql: Generational memory allocator

On 11/23/2017 11:04 PM, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
>> On 2017-11-23 22:34:57 +0100, Tomas Vondra wrote:
>>> Hmmm, I see. Presumably adding this to GenerationChunk (similarly to what we
>>> do in AllocChunkData) would address the issue:
>>>
>>> #if MAXIMUM_ALIGNOF > 4 && SIZEOF_VOID_P == 4
>>> Size        padding;
>>> #endif
>>>
>>> but I have no way to verify that (no access to such machine). I wonder why
>>> SlabChunk doesn't need to do that (perhaps a comment explaining that would
>>> be appropriate?).
> 
>> Can't you just compile pg on a 32bit system and manually define MAXALIGN
>> to 8 bytes?
> 
> I pushed a patch that computes how much padding to add and adds it.
> (It might not really work if size_t and void * are different sizes,
> because then there could be additional padding in the struct; but
> that seems very unlikely.)
> 

Thanks. Do we need to do something similar to the other memory contexts? 
I see Slab does not do this at all (assuming it's not necessary), and 
AllocSet does this in a different way (which seems a bit strange).

regards
Tomas