From: | Andres Freund <andres(at)anarazel(dot)de> |
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To: | David Rowley <dgrowleyml(at)gmail(dot)com> |
Cc: | PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Add palloc_aligned() to allow arbitrary power of 2 memory alignment |
Date: | 2022-11-14 22:11:43 |
Message-ID: | 20221114221143.sadq6mat3kf3oeal@awork3.anarazel.de |
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Lists: | pgsql-hackers |
Hi,
On 2022-11-08 14:57:35 +1300, David Rowley wrote:
> On Tue, 8 Nov 2022 at 05:24, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > Should we handle the case where we get a suitably aligned pointer from
> > MemoryContextAllocExtended() differently?
>
> Maybe it would be worth the extra check. I'm trying to imagine future
> use cases. Maybe if someone wanted to ensure that we're aligned to
> CPU cache line boundaries then the chances of the pointer already
> being aligned to 64 bytes is decent enough. The problem is it that
> it's too late to save any memory, it just saves a bit of boxing and
> unboxing of the redirect headers.
Couldn't we reduce the amount of over-allocation by a small amount by special
casing the already-aligned case? That's not going to be relevant for page size
aligne allocations, but for smaller alignment values it could matter.
Greetings,
Andres Freund
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