From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: Tomas Vondra <tv@fuzzy.cz>, Simon Riggs <simon@2ndquadrant.com>,
        pgsql-committers <pgsql-committers@postgresql.org>,
        Andrew Dunstan <andrew@dunslane.net>
Subject: Re: pgsql: Generational memory allocator
In-reply-to: <20171123214636.unwkrkunr7m2bkii@alap3.anarazel.de>
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Comments: In-reply-to Andres Freund <andres@anarazel.de>
	message dated "Thu, 23 Nov 2017 13:46:36 -0800"
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Date: Thu, 23 Nov 2017 17:04:36 -0500
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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 wh=
at we
>> do in AllocChunkData) would address the issue:
>> =

>> #if MAXIMUM_ALIGNOF > 4 && SIZEOF_VOID_P =3D=3D 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 wo=
uld
>> 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.)

			regards, tom lane