Horton

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

Frédéric Yhuel <frederic.yhuel@dalibo.com>

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From: Frédéric Yhuel <frederic.yhuel@dalibo.com>
To: Frits Hoogland <frits.hoogland@gmail.com>, Joe Conway <mail@joeconway.com>
Cc: Priya V <mailme0216@gmail.com>, pgsql-performance@lists.postgresql.org
Date: 2025-08-18T16:17:50Z
Lists: pgsql-performance 

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