Date: Thu, 26 Jun 2025 06:00:59 +0000
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Tomas Vondra <tomas@vondra.me>
Cc: Christoph Berg <myon@debian.org>, 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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Hi,

On Tue, Jun 24, 2025 at 10:32:25PM +0200, Tomas Vondra wrote:
> On 6/24/25 17:30, Christoph Berg wrote:
> > 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
> > 
> 
> Thanks! Now we wait ...

It looks like that the bug is "confirmed" and that it will be fixed:
https://marc.info/?l=linux-kernel&m=175088392116841&w=2

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com