From: Miod Vallat <miod@online.fr>
Subject: Re: uvm_swapout_threads() & freed pages
To: Martin Pieuchot <mpi@grenadille.net>
Cc: Mark Kettenis <mark.kettenis@xs4all.nl>, tech@openbsd.org
Date: Sun, 27 Oct 2024 20:01:46 +0000

> > Wouldn't it be better to make pmap_collect() return the number of
> > freed pages?  This is only actually implemented on i386 and it looks
> > fairly simple to count the number of ptp pages freed in
> > pmap_do_remove_86() and pmap_do_remove_pae() and have them return that
> > number.
> 
> I'd appreciate any help with that.   However there are other archs apart 
> from i386, what about sparc64, mips64, m88k and alpha?

Sorry to be late on this, lack of {spare time,bandwidth} as usual.

My own todo list mentions:

  * uvm_swapout_threads

     change the pmap_collect() interface to:
     - have a return value telling us whether it has freed mappings or not;
     - stop after N pages freed, where N will depend on how starving we are.

so I'll welcome any change compatible with this.

Note that however pmap_collect() does either way too much, or nothing,
in the current state; so after the return value change is implemented,
there will be work needed to make it work with a smaller granularity.

Passing the "number of pages to free" goal to pmap_collect() could be
worth doing as well.