Date: Tue, 24 Jun 2025 17:30:02 +0200
From: Christoph Berg <myon@debian.org>
To: Tomas Vondra <tomas@vondra.me>
Cc: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>,
	Andres Freund <andres@anarazel.de>,
	Tomas Vondra <tomas.vondra@postgresql.org>,
	pgsql-hackers@lists.postgresql.org
Subject: Re: pgsql: Introduce pg_shmem_allocations_numa view
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Re: Tomas Vondra
> If it's a reliable fix, then I guess we can do it like this. But won't
> that be a performance penalty on everyone? Or does the system split the
> array into 16-element chunks anyway, so this makes no difference?

There's still the overhead of the syscall itself. But no idea how
costly it is to have this 16-step loop in user or kernel space.

We could claim that on 32-bit systems, shared_buffers would be smaller
anyway, so there the overhead isn't that big. And the step size should
be larger (if at all) on 64-bit.

> Anyway, maybe we should start by reporting this to the kernel people. Do
> you want me to do that, or shall one of you take care of that? I suppose
> that'd be better, as you already wrote a fix / know the code better.

Submitted: https://marc.info/?l=linux-mm&m=175077821909222&w=2

Christoph