Re: An idea for swap partition size vs. swap space size in use handling

On Jan 22, 2023, at 06:11, Ronald Klop <ronald-lists@klop.ws> wrote:
> 
> 
> Van: Mark Millard <marklmi@yahoo.com>
> Datum: zondag, 22 januari 2023 05:41
> Aan: freebsd-current <freebsd-current@freebsd.org>
> Onderwerp: An idea for swap partition size vs. swap space size in use handling
> I have boot media that are each set up to boot a variety
> of systems that have widely different RAM sizes, from
> 1 GiBytes to 64 GiBytes for the aarch64 examples of this.
> 
> This has lead to having multiple swap partitions of
> various sizes so that I can have total swap spaces that
> are somewhat under the recommended maximum sizes for the
> amount of RAM in each of those systems that a given media
> can boot.
> 
> It would be nice if I could have just one swap partition
> on a given boot media, one that is more than sufficient
> in size for all but the biggest RAM system --but to then
> be able to tell the system to just use up to the
> recommended swap space size and to ignore any extra swap
> space in the swap partition.
> 
> If such could be done, I'd no longer use multiple swap
> partitions at the same time in order to get to a desired
> total for the system at hand at the time.
> 
> Of course, that still leaves what to do when multiple
> swap partitions are enabled if such a "ignore what
> would be extra" mode was also enabled. As I'd not use
> such, I've no specific recommendations to make that
> would make any difference to my use.
> 
> ===
> Mark Millard
> marklmi at yahoo.com
> 
> Â 
> 
> 
> Hi Mark,
> 
> Do you mean you would like to be able to add a "size" parameter to the fstab swap line?
> 
> /dev/da0p1      none            swap    sw,size=1g              0       0

No. That would use 1g for even the 64 GiByte RAM system
when I move the media to that 64 GiByte system and boot
it --and similarly as I move the media from system to
system in general.

For my style of use, I want the swap to be (a lower bound
approximation of) the recommended figure for the amount of
RAM for the specific system the media is currently use in.
That means that the figure changes when I move the media
to a system with a different amount of RAM.

> Another option I can think of is using the "gnop" geom provider. It has a -s parameter to set the size.

I classically use a label based path to identify the swap
partition, not a device name. This fits with the variations
in what system I'm booting and what other devices might be
around. (Some of the media involved here are USB media.)
Labels go at the end of partitions, as I remember. This
would appear to make forms of resizing or subranging the
partition also mean adjusting the labeling. That is
something I'd like to avoid.

I'd also like to avoid needing to provide my own lower
bound approximation of the recommended figure for the
live amount of RAM. For one, it is platform dependent,
for example armv7 and aarch64 are very different for
the same amount of RAM.

===
Mark Millard
marklmi at yahoo.com