Re: Safe vm.overcommit_ratio for Large Multi-Instance PostgreSQL Fleet

From: Frédéric Yhuel <frederic(dot)yhuel(at)dalibo(dot)com>
To: Frits Hoogland <frits(dot)hoogland(at)gmail(dot)com>, Joe Conway <mail(at)joeconway(dot)com>
Cc: Priya V <mailme0216(at)gmail(dot)com>, pgsql-performance(at)lists(dot)postgresql(dot)org
Subject: Re: Safe vm.overcommit_ratio for Large Multi-Instance PostgreSQL Fleet
Date: 2025-08-18 16:17:50
Message-ID: 6e36e010-c93c-4d9b-a7ed-db6da1416716@dalibo.com
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On 8/8/25 10:21, Frits Hoogland wrote:
> If swappiness is set to 0, but swap is available, some documentation
> suggests it will never use anonymous memory, however I found this not to
> be true, linux might still choose anonymous memory to reclaim.

A bug in RHEL8 meant that swappiness was not taken into account unless
cgroupv2 was configured or vm.force_cgroup_v2_swappiness was set to 1.
See references [1] and [2]. Could this be the cause of your observation?

[1] https://access.redhat.com/solutions/6785021
[2] https://github.com/systemd/systemd/issues/9276

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