Re: measuring swap partition speed

[For this message I'm replying to just the one point because I
expect that it is rather important to your context.]

void <void_at_f-m.fm> wrwote on
Date: Thu, 21 Dec 2023 15:50:52 UTC :

> On Wed, Dec 20, 2023 at 07:48:14PM -0800, Mark Millard wrote:
> 
> . . .
> Possible workarounds, bearing in mind 
> I'm not versant in C so it's not like I can fix this myself in code:
> 
> 1. swap as swapfile and not partition [a]
> 

I never recommend such because of the "trivial and unavoidable
deadlocks" issue. I just quote Konstantin Belousov on this
(copied from https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=206048#c7 ):

On 2017-Feb-13, at 7:20 PM, Konstantin Belousov <kostikbel at gmail.com> wrote
on the freebsd-arm list:

. . .

swapfile write requires the write request to come through the filesystem
write path, which might require the filesystem to allocate more memory
and read some data. E.g. it is known that any ZFS write request
allocates memory, and that write request on large UFS file might require
allocating and reading an indirect block buffer to find the block number
of the written block, if the indirect block was not yet read.

As result, swapfile swapping is more prone to the trivial and unavoidable
deadlocks where the pagedaemon thread, which produces free memory, needs
more free memory to make a progress. Swap write on the raw partition over
simple partitioning scheme directly over HBA are usually safe, while e.g.
zfs over geli over umass is the worst construction.

===
Mark Millard
marklmi at yahoo.com