Re: kern/56516: pgdaemon spins despite lots of memory available

[mlelstv%serpens.de@localhost (Michael van Elst)]

The following reply was made to PR kern/56516; it has been noted by GNATS.

From: mlelstv%serpens.de@localhost (Michael van Elst)
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: kern/56516: pgdaemon spins despite lots of memory available
Date: Sun, 21 Nov 2021 16:52:09 -0000 (UTC)

 he%NetBSD.org@localhost (Havard Eidnes) writes:
 
 >I got a tip to reduce kern.maxvnodes to about 1/10 of the current
 >value, and YES, this makes pgdaemon no longer hog the core:
 >    0   209 root     126 pgdaem/1  517:23  0.00%  0.00% pgdaemon  [system]
 
 >So ... this probably gives a lead to what's really causing this?
 
 With less vnodes the kernel needs less memory and you don't run out
 of (kernel-) memory that easily.
 
 When you kick pagedaemon to free memory, it checks some metric and
 if bad, it asks everyone (pools, cache, etc..) to free resources
 and it loops until the metric is good again. If the run doesn't
 actually free resources it will hog the CPU up to the point that
 some freeing operations don't even start.