Re: swapfile query

On Saturday, August 19, 2017 06:08:29 PM tech-lists wrote:
> On 19/08/2017 17:54, Cy Schubert wrote:
> > Then it doesn't matter if you use one or many swapfiles and deleting the 4 
> > GB won't make a difference. Just add the desired swap as required.
> > 
> > With 128 GB RAM you shouldn't be swapping anyway. If your system is you 
> > have more serious problems than the lack of swap.
> 
> The system is a bhyve host. There are 9 guests, two of them are
> freebsd-11-stable, the rest are ubuntu-14.04-LTS. Restarting some (but
> not all) of the guests has the effect of decreasing swap usage. The
> system also runs ZFS. The guests live on the ZFS filesystem.
> 
> The OS & swap on the host are SSD and are not part of the ZFS system.
> 
> What I'm seeing is, the host system won't touch swap for days. I guess
> when the guests get busier than an as yet unknown amount, the host
> starts using swap. The issue I'm having isn't so much it using swap,
> it's that the used swap seemingly is not liberated after it has been
> used, and I don't know exactly how to narrow it down.

Note that once memory is placed in swap, it won't be pulled back in until
some thread or process actually needs it.  If nothing needs the memory it
doesn't hurt to just leave it out on swap.  It might also mean that the
memory freed up by your temporary memory pressure from your guests will now
be available the next time you have memory pressure so that you won't have
to swap that next time.

-- 
John Baldwin