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From: Andres Freund <[email protected]>
To: Christoph Berg <[email protected]>
Cc: Tomas Vondra <[email protected]>
Cc: [email protected]
Subject: Re: pgsql: Introduce pg_shmem_allocations_numa view
Date: Mon, 23 Jun 2025 11:14:54 -0400
Message-ID: <g3mywoeo7jmh6rci7epx2ishowgz65q2j7ek3c5f3lxcmvuktg@ler2fsv4szmn> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>

Hi,

On 2025-06-23 16:48:27 +0200, Christoph Berg wrote:
> Re: To Tomas Vondra
> > Why do we try to force the pages to be allocated at all? This is just
> > a monitoring function, it should not change the actual system state.

The problem is that the kernel function just gives bogus results for pages
that *are* present in memory but that have only touched in another process
that has mapped the same range of memory.


> One-time touching might also not be enough, what if the pages later
> get swapped out and the monitoring functions are called again?

I don't think that's a problem, the process still has a relevant page table
entry in that case.

Greetings,

Andres Freund

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